CA1193737A - Automated data acquisition and analysis - Google Patents

Abstract

AUTOMATED DATA ACQUISITION AND ANALYSIS

Abstract A mechanized system distributing the access, test and communication functions to the point of testing, typically the centralized switching facility or wire center serving the customer loops to be tested. Computer stores information about each customer loop in the geographical area served by a system. Front-end computers interact with computer to retrieve pertinent data regarding loops to be tested. Each switching facility in an area includes a loop testing system that implements the required functions. The communication functions residing in front-end computers and loop testing systems are coupled via a data communication network in a manner that allows any front-end computer to communicate with any loop testing system. Users of the system control access and test from consoles having the capability of establishing independent communication paths over the national dial network for interactive tests on loops accessed through standard test trunks.
Microprocessor-based circuitry is utilized for numerous system tasks such as signal generation, digital signal processing and controlling sensitive analog measurements.
Signal generation includes digital generating of analog waveforms. Signal processing techniques incorporate various digital filters to analyze sample sequences derived from, for example, dial pulses and coin telephone signals.
Sensitive analog measurements of loop characteristics are effected with a magnetic current detector that operates over broad current and frequency ranges. Frequency dependent measurements are coverted to DC using synchronous demodulation techniques to enhance resolution.

Description

~3'7~7 Technical Field ~ ~ . . .
This invention relates generally to automated data acquisition and analysis and, more particularly, to a stored program control system ~hich directs a network of distributed processors.
Background of the Invention In order to test communication terminal and local ~ransmission facilities, referred to hereinafter as customer loops or simply loops, whether for fault diagnosis, preventive maintenance purposes or even to compile statistical information about loop characteristics, three basic functions are required, namely: access, test and communication. These three basic functions can readily be identified for any manual or automatic testing system.
E'or instance, within each system, there are mechanisms for gaining control of a loop to be tested, for connecting to it and for directing appropriate testing ac~ivities.
Moreover, a two-way communication path exists between testing personnel or equipment interfaces so that selected test activities may be initiated, ccordinated and the results collected for analysis. Oftentimes, an ~utomated central controller determines the testing pattern and analyzes results via interpretive algorithms.
One such computer-based system has been described in an article entitled "The Evolution of the Automated Repair Service Bureau with Respect to Loop Testing", published in the ConferenCe Record of the International Symposium on Subscriber Loops and Services, March, 1978, pages 64-68 as authored by O. B. Dale. The ~utomated Repair Service Bureau (ARSB)l which supports loop maintenance operations, includes the following maintenance functions: receiving trouble reports from customers;
trouble report tracking; generating management reports; and real-time loop testing and fault diagnosis. Thus, within the ARSB framework, there is provided a rapid, convenient method for testing and analyzing test results automatically at the time of customer contact 3S well as on demand during ~l93'73'7 repair procedures.
In order that the subject ~atter of the present invention may be elucidated, it is important to elaborate on ~he ARSB architecture and the cpabilities of the above-mentioned testing arrangement within this architecture. The information presented by this overview is set forth in the above-mentioned reference as well as in an article entitled "Automation of Repair Service Bureau", Conference Publication No. 137 of the International Symposium on Subscriber Loops and Services, ~ay, 197~ as authored by R. L. Martin. FIG. 1 indicates that the conventional ARSB comprises a tree-like structure with four major levels. At Level 1 of the tree is a data storage computer (200) which maintains a master data base of up to five million customer line records; the information on these records includes data as to equipment terminating the 1Oo2, loop composition, customer telephone number, and so orth. Level 2 is composed of an array of front end (FE~
computers (220,2~1), each of whic~ manages the bulk of the trouble report processing for about 500,000 lines. The users of the system, typically maintenance and craft personnel of the telephone company deploying the ARSB, interact with the system at this level. Level 3 is an array of control computers (240,241) that control access and testing and provide analysis of test results. Leve~ 4 comprises loop testing frames (250,251) which perform the loop accesses and actual test measurements via test trun~
connections to switching machines located in geographically-dispersed central offices.
Test requests from users are received and supervised by the FE computers and then performed by algorithms in the control computers and circuitry in the loop testing frames. The tests conducted are based on adaptive algorithms that compose test scripts in real time as a function of the electrical characteristics of the customer's equipment in the idle state. The data used are extracted from the data storage computer and then provided ~ . .

33'73'7 by the FE co~puters at the time the test request is generated. As testing on a customer's loop proc~eds, the test script is continually being revised to reflect the knowledge of the loop which has been gained from the test results. The final test results and analysis are formatted for display to the user by the requesting FE computer.
Varying levels of display detail, based on the technical sophistication of the user, are provided.
The loop testing subsystems of the ARSB were arranged to provide an area-based tabout 1 million loops) system in order to expedite its introduction and mitigate cost to users. As a result, not all of the testing functions of the standard pre-ARSB facility, known as the Local Test Desk ~LTD), were incorporated. For instance, the LT~ continued to be used for interactive testing between testers at the L~D and field repair craft. The loop testing subsystem could not be utilized to maintain a connection to the loop under test for a prolonged duration, nor could field repair personnel be guided throu~h a series of steps to diagnose, locate and correct a fault. In short, the loop subsystem was effective only in screening troubles and performing pre-dispatch and post-dispatch testing. Also, not every type o terminal equipment could be tested. For instance, coin telephone features were precluded from testing. Moreover, because the LTD operated within the same environment as the ARSB, the LTD was considered a backup during temporary outages of ARSB so there was no need for redundancy or fail-soft operation in the testing system. Finally, the area-oriented system was not cost effective for single wire centers serving only a few thousand lines.
With the above background, the problems encountered with the conventional ARSB testing system, including those emphasized above, may be summarized as follows: (1) no interactive testing capability with field craft personnel nor customers; ~2) inability to test coin telephone stations including such conditions as off-normal ~a~9~'73~

totalizers, stuck coin conditions, coin collect and coin return circuitry, and loop-ground resistance; (3) impossible to test and talk over the same test connection;
(4) no single- and double-sided resistive fault sectional-ization capability; (5) no ability to apply metallic orlongitudinal pair identification tones; and (6) no capability to control and monitor concurrent testing operations from a single work s~ation.
Summary oE the Invention In accordance with an aspect of the invention there is provided in a communication system comprising a plurality of remote wire line centers, each terminating a plurality of loops and associated customer equipments; a centralized facility for storing data concerning the loops and associated customer e~uipment in each wire line center; and an arrangement in the centralized facility for analyzing data from the wire line centers, characterized in that the remote wire line centers obtain and analyze the data from the loops and forward the results to the centralized facility over a switch transmission network.
The foregoing problems are solved by the employ ment of an arrangement for automatic data acquisition and analysis wherein the associated loop access, loop test and system communication functions are performed as closely as possible to the point of testing, generally within the individual wire centers serving the customer loops. The system utilizes the standard test trunks located within the wire centers for accessing the loops to be tested.
Broadly speaking, the system comprises: numerous autonomous computers which store information about loop composition and which are arranged with user stations for transmitting access and test requests and for receiving corresponding responses, and wherein each station is arranged with call processing circuitry to initiate or receive calls over the external communication network; a stored program controller, collocated with each wire ~L937;37 - 5a -center, for accessing and testing designated loops, and wherein each controller includes circuitry for establishing a communication path over the external network originating from the associated wire center; and a data communication network for communicating messages between each computer and a corresponding controller as determined by message content. Each user request is translated into a high-level message which is parsed and routed through the syste~
according to the message contents. One such user request effects interactive access whereby a user at a given station may be connected to an accessed loop. The access link comprises a communication path over the external network between the ,..~

~L~9373~

station and the particular wire center as well as a bridging connection to the accessed 1oo? via the test trunk. I`he message for interactive access contains callback information ~hich directs the controller to establish, concurrently, a call over the external network and a test trunk connection to the loop. Once the path is established, the system user may guide craft personnel in test procedures or contact the customer assignQd to the loop to request aid in testing terminal equipment. If required, the interactive path may be temporarily broken, tests may be performed on the loop and then the path may be reestablished to continue the work activity~
Brief Descri~tion of the Drawing FIG. 1 indicates the architectural arrangement of one conventional automated testing system and, in accordance with an alternative embodiment of the present invention, an arrangement for integrating the distributed Mechanized Loop Testing (MLT) system within the conventional system to expand test capabilities.
FIG. 2 depicts, in overview fashion, a block diagram of the major components comprising the stand-alone Mechanized Loop Testing system, as well as the interconnections among these components.
EIG. 3 depicts a three-tier multiprocessor realization of the Data Communication Network (DCN) shown in block diagram form in FIG. 2.
FIG. ~ illustrates the internal bus structures of the connection matrix and the connection arrays of the DCN~
FIG. 5 shows the flag-field pattern for a representative conventional high level data link protocol and, in particular, the location of the INFORMATION field within the pattern~
FIG. 6 indicates the composition of the INFORMATION field in terms of HEADER parameters and DATA
bytes utilized by the MLT system in message routing, loop access and loop test.

~93737 FIGS. 7, ~ and 9 show the microcomputer software architecture, in pictorial form, for tiers 1, 2 and 3, respectively, of the DCN. These illustrations are pictorial in the sense that they indicate a logical situation in terms of the number of copies of software utilized to implement the various system tasks.
FIG. 10 depicts the priority of execution of tasks within any of the microcomputers of the DCN. Both the initialization execution (top portion of FIG. 10) and execution with external event interrupts are illustrated.
FIG. 11 depicts, in block diagram form, a realization of the Loop Testing System (LTS) shown pictorially in FIG. 2.
FIG. 12 illustrates the DATA bytes in the I~FORMATION field for the regular or main distributing frame access request messaye as routed through the LTS of FIG. 11.
FIG. 13 illustrates the contents of an interactive re~uest message when both a loop access and a talk path to the Maintenance Center are to be established.
FIG. 1~ depicts the message returned from the port controller of FIG. 11 in response to an access request message.
FIG. 15 illustrates those DATA bytes extracted from the message format of FIG. 13 which are then utilized by the TCD task of the LTS controller Gf FIG. 11 to establish the actual callback path.
FIG. 16 is a depiction of the message format for a test request.
FIG. 17 depicts, in block diagram form, the circuitry comprising one Precision Measurement Unit (PMU) of FIG. 11.
FIG. 18 is a more detailed representation of the PMU controller, AC-DC source generator and digital signal processing portions oE the block diagrams of FIGA 17.
FIG. 19 illustrates the arrangement of memory bytes to realize the accumulator of the digital signal .:;

373'7 generator within the AC-DC source generator of FIG. 17.
FIG. 20 is a diagram, partly in schematic and partly in block form, showing one implementation of the -source applique of FIG. 17.
FI~. 21 indicates essential portions of magnetic current sensor circuitry of the detector portion of FIGo 17 whereby loop currents are transformed to equivalent volta~es.
FIG. 22 depicts the processing circuitry of the detector of FIG. 17 utilized to filter and scale the equivalent voltages.
FIG. 23 shows a block dia~ram representation of the measurement processor of FIG. 17.
FIG. 24 indicates the manner in which FIGS. 1~, 20, 22 and 23 may be arranged to form a composite representation of FIG. 17.
FIG. 25 indicates that the PMU task provides data to specify which of the many possible test requests is to be selected and, accordingly,` appropriate parameters are passed to the measurement cycle controller.
FIG. 26 depicts the sequencing of the measurement cycle controller for each configuration of PMU circuitry.
FIG. 27 illustrates the switcll matrices cosnprising the equipment access net~ork of FIG. 17 as well as the arrangement of various access and test circuits of FIG. 17 at the ports of the equipment access network.

Deatiled Description 1. THE MECHANIZED LOOP TESTING (MLT) ARCHITECTURE
The overriding architectural consideration employed in the MLT system is to distribute the access, test and communicaiton functions are closely as possible to the point of testing, which generally is the centrialized switching facility serving the subscriber loops to be tested. the deployment of such a distributed architecture minimizes data flow in the sytem, increases testing accuracy and expands test capabilities.
To place in perspective the descrition that follows, FIG. 1 illustrates, in overlay fashion, one arrangement for integrating in distributed MLT system within the framework of the ABSB system discussed in the Background Section. In this depiction, it is clear that one embodiment of the MLT system serves as an adjunct to the testing system described earlier. However, the illustrative embodiment of the present invention is best elucidated as a stand-alone system and this arrangement is shown in FIG. 2.
FIG. 2 depicts, in overview fashion, a block diagram of an illustrative embodiment of the MLT
architecture arranged in accordance with the present invention. Data storage computer 200 stores information about each subscriber loop existing in the area to be served by the MLT system. For instance, typical types of information accessible in computer 200 include the composition of the subscriber loop, office equipment, outside plant equipment and terminating equipment associated with each loop.
The area served by a MLT system generally encompasses a number of geographically-dispersed wire centers 150 and 151 containing switching machines 170 and 171, respectively. Individual subscriber loops 180, ..., 183, with associated customer equipment 190, ..., 193, respectively, are served by wire center 150,151 and connect to switching machines 170,171. Each wire ~9373~

center 150 or 151 served by the ~T syste~ ^ont~ins a collocate~ miccopr~cessor-b~sed Loo~ Testin~ System (LrS), 160 or 161, respectively, that also implements ~ccess, test ~ni _ommunication -apabilities (shown pictorially a, co~onents ~f ea_h ~rs 160 ~ 161 in FIG. 2). rhe a_cess portion of each LTa 15~,151 is ~rran~ed with circuitry for establishina a transmission connectio~, under -ontrol of FF computers 220,221, over the national dial nst~ork, that is, the Direct Distance Dialing (DDD) network, via facilities 932 and 933 emanating from ~ire centers 15~ and 151, r~spe-tively. Switching machines 170,171 are accessible from LTS 160,151 via test trunks 940,~41, re,Pectivelr~
Front-enl (FE) co~puters 220,221 interact with storage computer ~00 to retrieve pertinent data regarding subscriber loops to be tested. Since FE co~puters 220 and 221 are not ne~es,arily collocate with com3uter 200, ~ta links 900 and 901, respectively, are provided for intercomplter communication~ Direct communication between FE computers 220,221 is accomPlishe~ Yi~ Parallal Communication Link tPCL) 210 an~ interPosed ba~3e~ 310,311, respectively.
The c~mm~nication fun-tion, that ceside in ea~h LrS 160,161 ~nd in each FE computer 220,221 are coupled via

2; Dat~ Communication Network (DCN) 140. DCN 140 allows any one of FE computer, 220,221 to ~ommuniclte with any Lra 160,151 in any wire center 150,151 served by the M~r system. DCN 140 is also a micropro^essor-b~sed ~istributed processin3 machine that offload, co~muni-ation processing for all FE computers 220,221.
rhe ~rchitecture ~epi_ted in FIG. 2 allow~ any FE
_omputer 220,221 to test any customer loop 180, 0.., 183 within the area served bY the MLT syste~. ~o demon,trate this~ the following describes, ~gain in overview fashion, the operation of the illustcative eDbo1iD2nt of the M~T
system D

~1~3~737 A loop test ia typic~lly ~eneratel by a request from rePair service bureau personnel, typic~lly a maintenance admini,trator. Thi, user h~, a con~le 230,231 with ~n input/output device, e.g., ~ keyboard and cathode-ray tube (CRT), for interf~cing to ~ FE computer 220,221via data link, 312,313, re~pectively; the ~~n~ole ~lso inclules circuitry 235,236 for communicating over the DDD
network via conventional f~_ilities 914 and 915. ~averal types of CRT masks are available to enable the user to input dat~ ~e.~., a telephone number to be tested) ~nd receive output (e.~., test results) from the MLr systemO
~hen the user determines a subscribec 130p i5 to be tested, an ~LT ~rogcam resident on FE computer 220 or 221 requests that _ertain data base information be retriaved from ~torage computec 200 relating to the ch~racteri,tic, of a loop 180, ..., or 183 to be tested~ This information is utilized by an application Qrocass ca~ilent on FE
~omputer 220 or 221 that initiates acce~sin~ of the looP
~nd then ~uidea loop testin~. rhe ~Dplication process may contain, for instance, an adaPtive loop testin~ algorithm or it may -ontain commands to im~lement intec~ctive test control and othar functions similar to that Performed with manual te,ting.
Because of the procesaing cap~bility available in the micro~omputera of LTS 160,161, only high leYel ~ommands are generated bY FE comPuters 220,2~1. The first -ommand re~uests Lr~ 16~ oc 161 to ccess a ,pecified telephone number and, if interactive testing is required, the command also provides the telephone number of the circuitry at the user's console so a callback Path may be established, ~he message c~pilel by the appropriate FE ~omputer 220 or 221 to implement the command and transmitte~ o~er ~utg~ing data link 920 or 921 contains a mess~qe field h~ving a parameter that identifie~ which LTS d~ta link 930 or 931 is t~ be utilized for intercomPuter communication. ~ny ~essage, incluling the first one, is routed from FE -omputer 220 or 221 to DCN 140 via incoming data links 920 or 921 and, ~9373~

lfter aPpr~Driate ~arsing and raassembly ~f the mes~age, from DC~ 140 to the presele_ted Lrs 160 or 161 via outgoing data link 930 oc 931. rlhen acc~ss is c~mpl~te~, the response ia rerouted through data link ~3~ ~r 931, ~CN 140 ~nd data link 920 or 921 to the FE computer 220 or 221 that ce~uested the ~_ceas. Subs2quent message tcans~cti~ns that occur between F~ comPuter 22~ or 221 and Lr~ 160 or 161 involva hi~h lavel requesta for tests to be perf~cmed, followed bY det~iled responses _ontaining r~w test data (e.g~, the ~mount of current that ~s meaauce~ ~n loop wires 180, ... or 183 when a particular source was applied t~ the looP by LTS 160 or 101~ Th-se transactions may be prefaced with oral communications between the m~intenance - ~dministr~tor ~t console 230r231 and the customer serviced by the loo? or field craft pers~nne; at a l~c~ti~n ~lon~
the 1002- ~hese communications are transacted ~ver DDD
-allb~ck p~th ~nd ~re gener~llY utilized in the interactiqe test mode to establish a~PrOpriate conditions on ths loop Lor test purPoaes~ For example, a ~raftperson may be requestsd to short the loop so ~ DC resistance measurement may be effected. ~he last request made by FE c~m~uter 220 or 221 is to have LTS 160 or 161 disconnect from loop 180, ... or 183 under test. The number of loo~s that may be accessed simultansously at any LTS site and the number of simultaneous tests that may be in pro~ress at a given LTS
are discussed in the seguel.
rhe ~bove overview shows the baai~ design phllosophy of the MLT system anl illustrates one diatributed ~ro-esaing approach to loop testing. Hardware and software functions are Partitioned so that system -omplexity is reduced to tha point uhere basically inde~endentlY desi~ned and maintained modules interact via high level comm~nds. The following section describes the individual modules or comDonents of the MLr system i~
,omewhat more detail, but b~si_~lly still in overview fashion, from b~th a hardware and s~ftware pers~ective.
After ~his, another pass through each component will ~3~73~7 com~lete the detailed descriPti~n.
2. MLT IMPLEMENrArI0N
2.1 D_t__C~ _~nicati~n_NetwoEk_(DCN) 2.1a ~tr__t_Ee ~s inlic~ted in FIG. 2 ani allude~ to in ~he f~re3~ing discuasi~n, DCN 1~0 ia structured to route messages between anY FE comPUter 220,221 and ~ny LTS 160,161. rhe illustrative embolimant of D~N 140 to be ~escribed ~llows from one to twelve FE _omputers to exchange data with up to seven hundred ~nd ~ixty ei3ht (768) LOOD Testing Systems. (~his _apa-ity is determined by anticipated user needs; the total capacity of the ~rchitecture of DCN 140, ~ithout bu, extenl2r,, i, actu~lly 1568 d~ta links or~ e~uivalently, 1568 Loop Testing Systems.) FIG. 3 sho-~s a three-tiered m~ltipr~^ess~r realization of DCN 140. Tier 1 serial~in, Parallel~out devices 1401, ~.., 1412 are arrangel to accept inc~min~
data links 9201, ..., 9224 on a two data link-par-~aYice D~sis~ For instan~eS device 1401 in tier 1 interc~nnects to data links 9201 ~nd 9202. Incoming datl links 9201, ,.,, 9224 originate from FE computecs 220,221 ~f FIG. 2.
In fact, internal data link 9201 is the same link identified as external dat~ link 923, as depicted in 2; FIG. 3O A similar identificati~n may be maie between links 921 ~nd 9224.
Tier 3 Parallel-in, serial-out processing circuits 14001, ..., 14096 are ~rra~ed t~ Drovide ~utg~ing data links 93001, ..., 93768 on an eight data links-~er-30 -ir_uit ba,is. Outgoing data links 93001, , 93758 terminate on LTS's 150,161 ~f FI5. 2. In f ct, int~rnal i~t~ link 93001 is the sama link identified a, extecnal link ~30, as de~icted in FIG. 3. A similar identification may be made bet~een links 331 a~d 93768, rier 2 Parallel-in, ~rallel-out processing interface, 1421~ .~., 1468 serv- to interconnect first tier levices 1401, .,., 1412 and third tier circuits 14001, ~93~

14C96 by .~eans of _onnecting arrays 141, ..., 144 and _onnection matrix 145, shown in blo-k form in FIG. 30 FIG. 4 dapicts the actual arran~ement of arrays 141, 144 and ~atrix 145.
Nith reference to ~IG. 4, array 1'~1 (arrays 1!~2, 143 and 144 are substantially the same as ~rray 141) _om~rises three similar, but ind2pe~dent ~uasea 14121, 14122 and 14123. E~ch of these bus~as 14121, 14122, 14121 implements, in the ~referred embodi~ent, the General Purpose Interface ~us (GPIB) Pr~toc~l- Thia Pr~toc~l i, defined in IEEE Standard 488-1978 "Digital Interface or Programmable Inatc~entati~n," ~ well-kn~wn st~ndarl in the art of digital communication. ~atrix 145, comprising forty-eight si~ilar, but inlependent ~ussas 145501, 145502, ..., 145548, also utilizes the GPIB protocol. rne inter~onne-tions of the various busses are arranged to provide modularity and fail-soft oPeration of DCN 140, as now explained.
~he t~elve tier 1 devices 1401, ..~, 1412 of FIG. 3 are partitioned int-o grou~s ~f three devices-per-group~ For instance, the first group cont~ins devices 1401, 1402 and 1403. rhe circuit element, representing these devices have been labeled '1', '2', and '3', respectively, ~ithin the ~ict~rial reprasentation of each element. rhus, deVice 1401 has been designated with a '1', devi~e 1402 with a '2' and so forth. rhe numbers below '1', '2' and '3' in each oictorial representation, th~t is, '0', !1' and '2'p ~re indi_ative of the lo~ical ~ddresses to be associated ~ith the actual element numbers.
rhese logical desi~nations will be utilized to describe informati~n flow through DCN 140. Nith the above ter~inology, it is clear th t the seconl ~roup of devices -ontains device~ 1404, 1405 and 1406; theae are actuallY
the fourth ('4'), fifth ('5') and sixth ('6') devices havin~ logical deaignationa '0', '1' and '2'. Any ~ctu l designation (A1) can be converted to a logi_al ~esi~nation (L1) via the relation L1 = .~od (A~ 3~.

~L~g~ 3~7 ~ 15 -In the arrangement of FIG. 3~ thece are four ~c~ups of ~evicas. The devices in each group serve as inputs to a correspondin~ sonne-ting array 141, ..., or 144. For in~tance, devices 1401, 1402 anl 1403 of the first group are as,ociated with arr~y 141. Each device in tier I controls a unique meqns for transmitting information to and from it, a,,ociated _onnactin~ arr~y. F~r example, device 1401 controls transmission means 14101, which typicllly imple~ents the GPIB protocol.
Up to twelve tier 2 interfaces maY bs added per tier 1 ~rouP~ and this maximum is shown in FIG. 3. Sinee there are four 3roups and twelve interfqces ~er qroup, a total of fortY-eight interfaces are presont in the ~rchitecture of FIG, 3. These interfaces are 15 designated 1421, 1422~ , 1469 an~ corresPond to actual interfaces '1' through '48', respectively. Actuql interface lesi3nations (A2) al,~ have logicql ~esignati~ns (L2) /0' thro~gh '11' deterninei by the relqtion L2 =
DO~ (A2 -1~ 12).
Each tiar 2 interface has three input busses and ~enerates an independent output bus. For instqnce, interface 1421 is servel by busses 14104, 1410~ and 14106 and contr~l-- bu, 14501 on it~ o~tPut. rhe prot~col on these busses is typically ~he G~IB. The input busses 25 originate from ~ne of the conne~ting arrays 141, , 144 and the output bus terminatas on connection ma~rix 145~
~ith the above de,criPtion, the inter-onnocti~n ~rovided bY arr~Ys 141, ,.Or 144 may be des-ri~ed according to the follo~in~ t~bles.
TABLE I
Array 141 B_s Connects _o bussos 14101 14104,14107,14110 14102 14105,14108,14111 35 14103 14105,14109,14112 Array 142 ~193~73'~

nn_-ts t~ bus 14201 14204,14207,1421 14202 14205,14208,14211 14203 14205,14209,14212 TABLE III
Ar~ay 143 B~ C~nn__ts t~ buss~s 14301 14304,14307,1431 14302 14305,14308,14311 14303 14306,14309,14312 TABLE IV
Array 144 B~ _n_~ta ~ buss~s 14401 14404,14407,14410 14402 14405,14408,14411 14403 14406,14409,14412 rhe ~ocassing _iccuits 14001, .,~, 14096 of tier 3 are arr~nga~ to have an equal associ~tion with all devices 1401, ..~, 1412 o~ tier 1. From o~e t~ eight tier 3 circuits are allowed per tier 2 interface; the ~rrangemant o FIG. 3 sho~s the maximum li~it.
Cons2quently, the numbar of tier 3 circuits th~t aPPear is ninety~six, and these circuits ~re lab21ed '1' throu~h '96' in the pictorial cepresentation, of _ir_uits 14001 through 25 14096~ Corresponding to the actual desi~nations (A3) '1' through '96' ace l~gical design tions ~L3) '0' through '7' whi~h may be derivad from the r21ationship L3 =
mod (~3 -1, 8). Also, each of the ninety-six tier 3 cir~uits 14301 thr~ugh 14096 control, eight contigu~us 30 links comprising out~oing data links 93001 through 93768 _oupled to LT~a having actual lesignation~ '1' th~ough '768' in FIG. 3. Each TTS ~ith an ~ctual designation (A4) of '1' through '768' has a logical ~esignation (L4) determined by L~ - mod (A4 -1, 8).
FIG. 4 sho~s that circuits 140~1 through 14095 are divid~d int~ twel~e set~ with ea~h set _ont~ining eight _ircuits, and each circuit has four inpu~ busse~ and up to :~9~'7~'7 eight output data links~ For instance, circuit 14001 is served by in~ut bu,,es 145001 t~r~u~h 145004 origin~ting from matrix 145 and provides output links ~3Q01 throu~h 33008. ~ll input busses 145Q01 through 145384 ~ssociated with circuits 14001 through !~0~6 implement a parallel protocol, typic~lly tha GPIB, where~s output links 93001 thcough 93758 are serial transmissi~n link,. ~he pcotocol on the serial links will be dis^ussed l~terO
~he f~nction ~f matrix 145 is t~ inte~connect busses 14501 through 14548 arriving at its in~ut to busses 145001 through 145384 exitin~ its output~ rhe data bus means dePicted as matrix 145 in FIG. 4 ~ccomplishes this function. Matrix 145 comprises fo~ty-eight si~ilar but indspendent busses 145501 through 145548 im~lementing the GPIB grot~c~l. On the input sile of matrix 145: incoming bus 14~01 connects to internal bus 145501; inc~ming bus 14S02 _onnacts t~ internal bus 145505, incoming bus 14512 connects to internal bus 145545; in~o~ing bus 145513 con~ects t~ intern~L
bus 145502; and so forth.
On the outPUt si~ of matcix 145: intsrn l bus 145501 connects to outgoing DUSSeS 145004, 145008, .0~, 145032; internal bus 145502 connects to out~oin~
husses 145003, 145007, ...~ 145031, intern~l bus 145503 connects to o~t~oing busses 145002, 145006, ..., 145030, intern~l bus 145505 connects to outgoing busses 145036f 145040, ..., 145064; and s~ forth.
rhe interconnection arrangement ~f matrix 145 may be ~ummarized ~ith the aid ~f a sh~rthand n~tation, as follows: if interfaces 142l thr~ugh 1468 ar2 r2presente by the n~tati~n i(1j, i(2), ..., i(48), resPe~tivelY, and the twelve sets comprising circults 14001 throu~h 14096 by m ~ = 1, 2~ ..., 12, with m = 1 c~rre,p~nlin~ t~
circuits 14001 through 14008, and so forth, then matrix 145 maps tier 2 interfaces an~ tier 3 -ircuits ~ccording to the relation i (m ~ 12 (n-1)), n = 1, 2, 3 ~d 4.

37~

For e~amPle, with m = 1, then interfaca devices i(1), i(13), i(25) an~ i(37), corresp~nding t~ actual devices 1421, 1433, 1445 and 1457, serve ths sat containing circuits 14001 through 14009.
2.1b M_s_3q2_R_utin~
With reference t~ FIG. 2, dat~ links 920,921 arriving at the input to DC~ 140 and outgoing lata lin~s 930,~31 ~eparting DCN 140 utilize a seri~l mo~e of transmission and a protocol that is bit orient2~.
Informati~n is transmitted ~ver the,e link~ in communication elements c~lled frames. rhe bit pattern of a typical frame is shown in FIG. 5; this ~attern is represent~tive of conventional high level data link control type prot~cols. One exa~pl~ of a conventional link level (oftentimes designated Le~el II) protocol is the well-known aynchronous data link control ~DLC) protocol. I~ith these protocols, the comD~nents ~f a frame in-lu~a:
(1) an ei~ht bit OPENING FLA~ fi~ld to in~icate the start ~f a frame;
(2) ~n eight bit ADD~ESS field i1entifying the receiving station that is contr~lled by the transmitting ,t~ti~n;
(3~ ~n eight bit CONrROL field used by the transmitting ~tati~n to control the re-eiYin~ atati~n and ~5 by the latter station to respond to the foc~er station;
(4) a variable length INF~RMATION field containing the message that is to be transmitted without -onstraint, on length or bit patterns;
(5) ~ sixteen bit FRAME CHECK field to detect transmissi~n ecrocs; and (6) an ei~ht bit CLO~ING FLAG field to indicate the end of a frame.
Of pcimary import~nce in the tran,mittal ~f messages within the ~LT system is the data ~ont~ined in the INFORMATI~N field. In general, MLT mes,age, have the format shown in FIG. fi. The message comprises a HEADER
portion and a DATA Portion~ The HEADER in-luie, a number '73~

, g of bytes to indicate: ~hether the ~esa~ge is ~ re~est or response ('request_response'), routing procedure ('up_route' ~nd 'd~wn_route'); the ~COC255~C whi_h is the source ('up_cir^uit_type') ~nd ~estination ('lown_circuit_tYpe~); the software task at the source ('uP-task-id~) ~nd the destination ('down_tlsk_id'), an~
other bytea to be discussel lat-r. rhe ~ATA Portion contains a vari~ble number ~f bytes pri~arilY indicating the type of tests desired and the raw data measured as a ~esult of these te,ts. Theae DATA bytea will be diacus~ed in detail later.
P~rti_ulacly pertinent to mes,age couting in DCN 140 are the 'do~n_r3ute' anl ~uP_route~ bytes.
~henever a message is sent from a FE com~uter 220 or 221 to a LTS 160 ~r 161, ths 'down_route' para~eter, comprisin~
two bytes~ ~u,t be parsed iQ orler to g~id_ the ~eaaage through the three tiers of DCN 140~
~ s an ex~mPle, it is sup~osed th~t a FE
c~mputer 220 oc 221 is to inter~ct with an L~S that has an actual deaignation of '121' in FIG. 3. The actlal ~eci~al desi~n~tion is ~ecremented by one to yiald ~ de_imal value ~f 120 and thia ia cepresented in '~o~n_c3ute' by the following bit p~ttern:
bit position 15 14 13 12 11 10 9 8 value O O O O O O O O
bit position 7 5 5 4 3 2 1 0 value 01 1 1 10 0 O.
In general, bit p~aitions 0, 1 ~ni 2 ~re u,ad by tier 3 circuits 14001 through 1409~ to decide which one of its eight associated oltgoing d~ta links 93001 through ~3758 uill be used to transmit the INFORM~TION field to the ~ppropriate Lr~ ('121' in this example). ~it D~aition~ 3, 4 and 5 are use~ by tier 2 interfaces 1421 through 1468 to decide uhi~h one of its aight aasociated tier 3 circuits 14001 through 14096 will receive the INFORMATION

~9~
- 20 ~
field. Finally, ~it Dositions 6, 7, 8 and 9 are used by tier 1 devices to decide which one of its twelve corresponding tier 2 intarfaces 1421 through 1458 will reoeive the INFORMArION field. In this exq~ple, pacsing of the 'down_route' t~o byte p~ram-ter in oonjunction with reference to FIGS. 3 and 4 indicates that:
(i) tier 1 device 1401, 1'~02, ~.. or 1412 (saY
1403) receivin~ the fr~me p~sses the INFORM~TION field to the tier 2 interface having logical address (L2) of '1' (binary 0~01 is e~uivalent to decim~l 1);
(ii) tier 2 interfac_ 1422, corresponding to lo3icql a~dress '1', receives the INFOR~ATI~N field and passes it to the tier 3 cir~uit having logi-al address (L3) of '7' (binary 111 is decimal 7); and (iii) tiar 3 cir_!1it 14015, c~rres~on~ing to logic~l address '7', passas the INFORMArION fiald, qfter ce~ssembly into a data link protocol, to the LTa having logical address (L4) of 'O' (000 in binary is decimal 0)~

As indicated in FIG. 3, the L~S having logi-al address 'O' qt the output of a_tual tier 3 -ircuit 14015 is tha L~S
labeled '121', as requested.
~ henever any tier 1 devica 1401 thro~gh 1412 re-eives q frama on its data link conne_tion to FE
computer 220 oc 221, this is an indic~tion that the INFORHATI~N field contained in the fra~.e is to be Dropa~atel in tha ;o-callsd D~r~N dicection thr~ugh the MLT
architecture of FIG. 2. Tha p~rameter in the H~ADER
pocti~n of the INFORMATION fiel~ indicating the ~ltimate destination is 'down_circuit_tY~e', which ~ill be discussed later. The specifi~ path throu~h DCN 140 t~ this destination is found in 'down_route', as exemplified above.
A si~ilar protoc~l is observed f~r messagas traveling in the so-called UP direction of the hierqrchy~
In UP transmissions, the pertinent ~ADER pqrameter, are 'up circuit_typa' and 'up_route'. As a message is passed DOWN the hierarchY by DCN 1'~0, qppropriate ceturn

3'73'~

_ Zl _ - informati~n is saved i~ 'u~_cir_uit_type' and ~,sembled t n 'up_route' to ~llow for an orderly progression UP the hierarchy. The bit Positi~s ~f 'u~ ro~te' ar~ interpreted ~s follows: (1) bits 4 an~ 5 are employed by tier 1 ~evices to indicate the return Path on one of two d~ta links ass~_iated ~ith each levi_e 1'~01 thr~gh 1412;
(2) bits 2 and 3 are used by tier 2 interf~ces 1421 throu3h 1458 t~ return on one of three bu,,as ~nnectin~
each tier 2 int2rf3_e to its associ~ted connecting lrray 141, .,. or 144; (3) bit, 1 ~n~ O ~ce utilized by tier 3 circuits 14001 through 14096 to return ~n one of four bussas connecting each tiar 3 ~ircuit to conne-tion matrix 145~
In the exam~le given ~bove foc r~tin~ in ~he D~N dire-tion, it is supposed, as above, th~t tier 1 device 1403 received the frame ~nler con,iler~ti~n ~n link 920~, as shown in FIG. 3. This link h~s l~gical ~esignati~n '1'; in fact, the lsft hand, incoming d~ta link associated with eacn tier 1 device is the '1' link whereas the other link is designated 'Q', by conventi~n. Be~re routing the INFORMATION field to tier 2 interf~ces, the logical designation is converted to bi~ary ~nd bits 5 and 4 are filled with the binary re~resentation - in this case ~1. Tier 2 interf~ce 1422 ceceived the message on bus 14109 from ~rray 141 (FIG. 4); this bus is desi~nated by ~ logi-~l 'O'; in f~ct, the three busses entering a tier 2 intecface fc~m an array 141 thcough 144 ~ce labeled 'O', '1' and '2' starting with the right-mo,t bus~ Then, before sen~ing the message to tier 3 circuit 14016, bit, 3 and 2 are given the values 0 and 0, resPectively ('O' in ~ecimal convert, to 00 in t~o-bit binary). Finally, since tier 3 cir_uit 14016 receives the message on its lo~ical '3' bus from matrix 145 (ag~in, the rig~t-~st bus is logical 'O' and the left-most bus in logical '3'), bit positions 1 and O are fillel with 1 and 1, cespactively ('3' in decimal converts to 11 in binary). To summ~rize for this exampla, the LTS h~ving actual address A4 = 121 ~l~g3~73'7 receives ~ fr~me with the 'up_route' Parameter of HEADER
filled as follows:
bit ~sition 7 6 5 4 3 2 1 0 value - - 0 1 ~ 0 1 1.
(Bit positions 5 and 7 ~enerally havs values ~ut are not pectinent to the iDmediate liscussion and, thecefore, have been shown without ralues).
As indicated in FIG. 3, each tier 1 levice 1401,..., or 1412, receives two dat~ links at its input. Since the typical MLT system is implemented with twelve on line FE computers, ea_h FE computer 22~ or 2~1 ,Up2octs two l~ta links at its output~ To provide ~ degree of redund~ncy f~r fail-soft operation, FE ~omputers 220,221 and tier 1 devices 1401-1412 are interconnecte~ ~o that there are t~o Possibls paths betweer ea_h FE comPUter 220 or 221 anl DCN 140. For exam~la, FE co;~put~r 220 sup2octs the two data links 9201 and 9219 that terminate on tier 1 livices 1~1 an~ 1410, respectively. Simil~rly, FE
comPUter 221 imPlements two data links which t2rmin~te on ~evices 1412 anl 1409. ~.~ith su-h a FE-to-D~N c~nnecti~
arrangement, if one of the FE-to-Lr, ~aths _omprising the input data links 32~1-9224 and DCN 140 fails during a tcansaction, it is Possible to re-route the results from the given LTS to tha appropriat~ FE computer over the alternate path. The folowin~ pcoce~ure implements the the ~lternate routing technique.
Each FE -omputer 220,~21 is initialized with a unique identifier. This identifier is storad ~s part of the 'logi~ ' byte of the message HEADER, as diPicted in FIG. 6, for all mesaages ori~in~ted by the ~sso_iated FE
computer. ~he 'logical_id' is not related to the _tual physi~al ~onnection to DCN 140. ~hus, if a FE computer fails and is ceDla-ed by a back~p -~mputer, tha ba_kup inherits the identifier of the FE comPuter bein~ replaced.
As a ,~essage travels DO~N the hiecarehy, information about the return Path is store~ in 'up_route', ~lg3737 ~s ~escribed above. ~hen the messa~e reaches the le,ignated one ~f the tier 3 ciccuits 14001-14096, the -ompleted 'up_r~ute' byte ~nd ~ssociatel 'logic~l_id' byte may be extracted. ~ach tier 3 circuit maintains a table _ontaining the two most recentlY used up~ar~ pqt~s for each 'logical_id'. Sin_e the instru-tion routines controllin~
FE computecs 220,221 seneraLlY iistribute infoc,nati~n transmissions e~uallY throu~h DCN 14Q, the table for a ~iven FE _omput2r, at any one time, will contlin 'up_route' in ormation on the two ~ost recent Paths neede1 to reach the particular FE com~uter in UP tr~nsmissi~ns.
If an upward mess~ge -onnot re~ch the destination FE computec ~ia it, ~uP-route~ inf~cm~tion bec~use ~f a primary Path blockage, the message is m~rked as failed and sent back to the originatin~ riar 3 _ircuit. rhe table entry for the same 'logical_id' is ccessed and the 'up_route' information is repla_ed with the alternate or secondary 'up_route' path. If ~ny subsequent failures occur, the message is then disc~rded.
In some situations, it is ~ossible that the two most cecent entries in the table do not correspond to the 'up_route' bYte in the UP messa~e. This o_-urs in ,ituations where long-term craft activities are in progress, such ~s p~ir identifi-ation with an identifier tone provided by the NLT system. If a mess~e fails to tcavecse the UP path on its first attempt, then either path in the table may be used as an lternate route~
2.1c ~oft~aE__Desian Each mi~roprocessor executin~ within DCN 140 runs under supervisi~n ~f its o~n ROM-ba3a1 ~pec~tin~ system.
~owever, each separate operatin~ system is identical, so ~nly this one ~Der~ting system, designated ~S, reguires explanati~n.
rhe O~ pcovides a multitasking anvironment so th~t the operations performed by in~ividual modules comprising the three-tiers 3f DCN 140 can be Partitioned into ~ series of suboperations ~alled "tasks". Eacn task ~9.~7~7 - 2~ -is dedicatad to han~ling a speciali~ed activity. The OS is acranged to in~lre that the appcopciate task g~ins control of its associated microprocessoc and commences execution of its progr~mmed se~uence when a Particular activity is ~e~uested. F~r exqm~le, one ta,~ reaident in D~ 140 ia lesigned t~ hanile GPI~ activity; this task exe-utes whenever a bu, transfer is re~uired ~ver any one of the numerous GPIB-type busses embedled within D-N 1!10.
I~henever a bus tranafer is complete~ ani no other tcansfers ~re required, the bus transfer task relin3uishes control of its micropcocesaor, and other s-heduled taaks ace now free to execute and satisfy re~uests for other a^tivities~ If no ~ctivities are scheduled, the OS is in its ~ait atate, testing for a flag; a flag is set whenever a ~articular activity, and its associated ta~k, await ex2cution.
rhe microcomputer archite-ture, in Pictorial form, for each tier of DCN 140 is shown in FI~. 7~ 8 and 9 for tier 1, tier 2 ar.d tier 3, respectively. ~here are, at most, six types of t~sks imPlemented by any particular microcomPUter within the hierar-hy of DCN 140.
Five of these tasks are shown in FIG. 7, which lepicts the ar-hitectural arrangement or tier 1 device 1401 (the remaining tier 1 devicas 1402 throu~h 1412 have essentially the sams architectural arr~ngement as levic~ 1401 and, therefore, device 1401 is taken as ce~cesentative)~ The task dssi~natad SERIAL DArA within elements 11405 and 11406 of FIG~ 7 contcols tha activity ~aaociate~ ~ith information transfer over aerial data links 9201 and 9202, respectively. This task (i) p~rses incoming ~rames (FIGr 5) received over ~ d~ta link 3201 or 9202, extracts the contents of the INFORMArION field, and atores the contenta in a buffer memorY within the _ontrolling microprocessor that is ~ccessible to other t~aks; and (ii~ performs the inverse to ~acain3 on outgoing frames, that is~ constructs a frame for transmission bY
axtra_tin~ tha -ontents o buffer memory to orm the INFORM~TION field of the fr~me ~nd ~u~ments this fiald with ~g37.~'~
- 25 ~
the other fields (FIG. 5) needed for the sarial protocol on links 9201 ~nd 3202.
~ he t~sk labeled PARALLEL OU~PU~ within element 11407 c~nt~ols the tran,fer of inf~rm~ti~n ~ver par~llel-oriented bus 14101 and, when requi~ed, serves as the bus master. Information requiring transfer is ~xtracted fro~ ~r atored in buffer ~emory a-ces~ible by other task~.
rhe ADMINISTRATION task, represented by ~lement 11409, performs all non-oper~ional functions re~uired in the local environment. ~or instance, ADMINISTR~rION _ontrols aanity ~nd ~iagnostic testing and the rs~orting of trouble. With reference to FI~ 6, ADMINISTRA~ION utilizes 'up_cir_uit_type', 'd~wn_circuit_tyPe', 'up_task_id' and 'down_task_id' for ^ommunicating with other MLr mi^rOCODpUterS to synchronize testing among the various modules.
rhe DUMP MEM task, represented by element 11411, waits a cert~in peciod after a reset or restart operation and determines if a snapshot of tier 1 memory is to be sent to a FE com~uter 220 or 221.
rhe BROADCAST task, depicted by element 11412, ceplicates a messa~e for transmission in P~allel to tasks havin~ a plurality of appearances within a particul~r tier ~c, in thi~ case of tier 1, to ~ERIAL DA~A ta~ks 11405 and 11405. Replication reduces throughput time b~ allowing ,everal slow serial transfers t~ ~r~ceed in para~lel~
rasks ara defined so that the programs executing in the microco,~putecs ~E DCN 14~ ar~ relatively independent of the hardware they control. rO accomPlish this, ~enerally e~ch har~ware component h~ving in~ut ~r ~utput (I/O) c~PabilitY has both a harlware driver an~ a softw~re buffer th~t a_-omp?ny the sole task controlling that I/O
capability. Up~n system initialization, a unique memory block is defined for each I/O h~rdw~ce comp~nent; this block is known only to the hardware driver ~nd software buffer as,ociatad with each I~O request. rO service an I/O

~3'~3~7 re~uest, the buffec routine fills the aoproprilte msmory bl~k with cont~ol Darameters and signals the driver to start I/O processin~. The I/O oper~tion is completed by the drlver at interruPt level.
Whereas the only _onnacti~n b3twQ3n the harlware lrivar anl buffar software is the _ommon memory block, the only connection between the driver ~nd the qssociated task is a flag or semaphore that is set by the ~river whan its activity renuires execution. The tqsk awaits the 1~ oc-urrence of the semaphore, after which tha t~sk is scheduled bY OS. In this manner, a task never -ommunic~tes ~irectly with ~ hardware driver.
With reference to FIG. 7, the driver ~nd software buffer functions associated T~ith the incoming links 92~1 an~ 9202 ~nd outgoing bus 14101 may be identified. For instance, INPUr DRIVER 11401 anl INPUT 8rJFFER 11403, interposed bet~3en incoming data link 9201 and SERIAL DATA
tqsk 11405~ perform the desired buffering on incoming link 9201. To transmit a ~essa~e batwean SERIAL DA~A
task 11405 and ~UFFER 11403, tha ta,k makes a function call anl pqsse, appr~priate ~aranetecs (e.g.~ the ~amory address of the assigned memory block an~ the ad~ress of the -om~letion semaphoce) to the functi~n. The fun_ti~n th~t is called is raferr-d to as the buffer routine, and it is this routine thqt i, rePre~entel pi_torially by element 11403 in FIG. 7.
Fc3m FIG. 7 it mq~ al30 be observed that INPUT
3UFFER 11404 anl INPUT DRIVER 11402 serve to interfqce ~ERIAL DArA task 11406 and incoming data link ~202, wheceas OUTPUT BUFFER 11408 and ~IJ~PUT DRIVER 11410 service PARALLEL OUTPUr ta3k 11407 qnd parallal-ori3nt3~ bu, 14101.
rhe one task remainin~ to be ~efined is the PARALLEL INPUT task represented by elemant~ 11427, 11428 and 11429 in FIG. 8; this figura pi-torially r3presants tisr 2 intarf~a 1421 (the cemainin~ tier 2 intarf~_es 1422 through 1458 h~ve essentially the slme architectural arran~ement a3 interface 1'~21 qnd, therefora, 3~

interface 1421 is t ~en as ~e~resentative). rhe P~RALLEL
INPUT task org~nizes messa~e tr~nsfers ~cross the parallel-input bua,es 14104, 14105 ~nd 14106 vi~ th~
individual tasks 11427, 11428 and 11429, respectiveLy.
rhese three ~ARALLEL I~PUT tasks run under control ~f ?ARALLEL OUTPUT ta,k 11407 ~f FIG. 7, whi~h i~ the bus master. I~PUT D~IVER and INPUT 3UFFER Pairs 11421,11424;
11422~11425; and 11423,11425 ser~e basi-ally the a~e ~unction as INPUT DRIVER anl INPUr BUFFER
10 pairs 11401,11403 (~r 11402,114~4) ~r FIG. 7, that is, they indirectly couPle PARALLE~ INPUr tasks 11427, 11428 and 11429 to incoming p~rallsl buss~s 14104, 14105 and 14105, respectively. The pri~ary differen^e lies in the ~rallel bit orient~tion of busses 14104, 14105 ~nd 14105 a, 15 contrasted to the serial protocol of links 9201 and 9202.
~DMINISIRATION task 11430, ~ARALLET ~u~PUr task 11431, DUMP MEM task 11434 and BROADCA~T t~sk 11'135 of FIG. a are the aquivale~t of ADMINI~TRArI~ task 11409, PARALLEL ~urPu~ task 11407, DUMP MEM task 11411 and 20 BROADC~ST task 11412 of FI~. 7.
FIG. ~ depicts, in pi_torial fashion, the ~rchitacture of tier 3 vithin DGN 1~0. The f~ur el2ments labeled 114009 thr~ugh 114012 repressnt the PARALLEL INPUT
task asso_iate~ with incoming, par~llel-oriented 25 busses 145001 through 145004, res~ectively. Essh ~A~ALLEL
INPUT task perf~rms in essentially the same manner as e~ch PAR~LLEL INPUT ta~k 11427, 11428 ~r 11429 of FIG. 8. In ~ddition, Qach PARALLEL INPUT t sk is indirectly coupled to its associ~te~ hardware Vil an INPUr DRIVE~ and INPUT
30 ~UFFER, a, depi~te~ by element 2airs 114001,11400C;
114002,114006; 114003,114007; and 114004,114003. rhe~e pairs oPer~te b~si_ally the same as INPUT DRIVER and INPUT
BUFFER ~ai~s 11421,11424; 11422,11425, ~nd 11423,11426 ~f FIG. 8.
rhe eight elsments designated 114014 through 114021 represent the SERIAL DAT~ tas~ asso-iate~ with outgoing, serially-oriented links 33001 through 93008, ~93'7~

cespe~tively. rhese ei~ht tasks are equivalent to SERIAL
DATA task 11405 and 11405 ~f FIvo 7. Also, ea_h SERIAL
DATA task is buffered from its 4ssociated h4rdw4re via ~n ou~Dur DRIVER a~d OUTPUT BUFFER, as depictel by the eight ~lement p4irs 114022,114030; ...; 114023,11~037. These eight element P~irs are the cour.terPart to INPUr DRIVER and INPUT BUFFER pairs 11401,11~03 ~nd 11402,11~Q4 of FIG. 7.
Finally, AD~IINISr~A~ION task 114013, DUMP MEM
t4sk 114038 and BR3ADCAST task 114C39 of FI~. 9 serve to -ontr~l tier 3 micr3computers in a ~anner e~uivalent to t4sks 11409~ 11411 and 14112 of FIG. 7 or t~sks 11430, 11434 and 11435 of FIG. 8.
~ IGS. 7, 3 and 9 4re Dictorial in the sen,e that they indi_4te a logical situation in terms of the number o~
sopies of softw~r_ utilize~ to im2lement the tasks~ For example, the tier 3 archite-tura of FIG~ 9 indi_ates there 4re four ~istin~t ~ARALLEL INPU~ tasks 114009 throu~h 114012 and eight distinct SERIAL DArA t~,ks 114014 through 114021. Actually, there is only one CODy of the PARALLEL
20 INPUT Pro3ram ~nd ~ne co2y ~f the SERIAL DArA pcogram stored in microcomputer 14001. There are four distinct read/write (R/W) memory re~ions or ,tacks dedic4te~ to PARALLEL INPUT tasks and ei3ht listinct R/W st~cks dedicated to SERIAL DATA ta,ks, The st~te ~f e4ch task is kept in the appropriate stack. The OS retains Parameters indicating where, within e~_h stack, the task ,hould commence sxecution of an activity re~uest.
rhe environment lescribed immediately ab~ve basically defines the concePt of a multitaskin~ operating system. In ter,ns celated t~ ti3r 3 interf~~2s, multitasking obtains be~ause four independent PARALLEL
INPUT pro~rams ~ra executed fro~ within four di,tincts environments by the central pro~essing unit of each ~i~ro_omputer, namely, the four PARALLEL INPUT ~a,k, 11~C09 through 114012. Similar remarks aPPlY to the eight SE~I~L
D~A tasks 114014 through 114021 OI FIG. 9.
2.1d S_~tw_Ee_ Qo_Eatlon ~3~

~ o understand how each or the mi-rocomputers embedded in DCN 140 operates in terma of an unf~lding sequence in time, processing circuit 1401 of FIG. 7 is _onai~erel ~s exemplary. As Praviously di,~ussad, there ~re six applic~ti~n tasks and their intera~tion with the OS
to consider. ~owever, the concepts ~ay ~e ceadily _onVeyed by Presenting the interaction of a subset of these tasks, namely, SE~IAL DATA, PAR~LLEL OUTPUr an1 ADMI~I~TRArION, as now ~iscussed. At system startup, the OS commences axe_ution bY: (i) initializing its ~ss~ci~ted intecnal random-access memory; (ii) org~nizing memory blocks to serve as message buffers and pl~cin~ these buffer l~cations onto a list called the FREE buffer list; (iii) scheduling each task to run according to a preselected priority; and (iv) shifting exe-ution to the SCH~DULER program. Since the only tasks that have been s~heduled to this point in the execution ~re those arranged in pre,ele-ted order, the SCHEDULER finds th~t the first task, design~ted Task 0, is READY to RUN. Ia,k O contr~ls ths in~o~in~ d~t~ link having logical designation 'O', so with reference t~
FIG. 7, Task O is identifiel as SERIAL DArA task 11405 and its associated lata link is lina 9201.
Just prior to transfecrin~ execution t~ r sk o, the SCHEDULFR i~entified the st~ck to be associated with ~5 rask 0. Once the stack locatio~ is identified, executi~n of ~ask O commences from the first program statement.
Since Task O c~ntr~ls a serial 1ata link (link 9201 having logical designation 'O' in FIG. 7), the task b~ins by m~kin~ a system call to OS to obtain an un1,ed me~,~ge buffer fr~m the FREE list of buffers ~nd thsn sets up data link INPUI BUFFER O program (element 11403 ~f FIG. 7) to re~eive d~ta into the now allocated buffer. Task O then initializes link 9201 by arranging ~nd sending a data link start-up message. Task O finalLy r-lin~ui,he, ~~nt-ol the cantral ~ro~essing unit (CPJ) of its associated microcomp~ter by making a system c ll to 0~.

, .

~ 373'7 ~ 30 -~ he 0~ SCHEDULER prosram is entere~ ~3~in and, sin^e the initi~lization 2rogram of OS has ~ade all tasks READY to RU11, Task 1, haYin~ the next highest priority~ is RE~DY to RUN. ~he CPU is a~ran~ed t~ sxe~ute in the st~ck environment of Task 1, and ~ontrol is ~hen ~assed to rask 1. rask 1 begins to execute from the flrst st~te~ent in its pr~ram.
Since Task 1 controls data link '1', (link 9202 in FIG. 7), it executes essenti~lly the sama Pc~gra~ as did rask 0, the only difference being that the stack areas in memory ha~e different location,. A view ~f the st~ck associated with Ta~k O at this Point in the execution of ~ask 1 indicates a ~ait state in ~hich ~ata link ~2~1 is set up to receive d~ta and a data link start-uD message has been transmittel. In contrast, the stack of Task 1 indicates that link 9202 is ~uiescent. However, upon relinguishment of the C~U by Ta,k 1, its associ~ted sta^~
is also primed in the ~ait state.
Tha SCHEDULER pro~ram fin~s T~sk 2 READY to RUN.
rhis task is the one depicted as PA~ALLEL OUTPU~ t~sk 11407 af FIG. 7 ~nd ~ontrols parallel-oriented bus 141010 Basically the s~me Qrogram seau3ncin~ o--urs in ~ask 2 as in the prior task executions. rhe CPU is arran~ed to ~perate in the ~tack environment o~ ~ask 2, and ~e~ins by executing from the first st~tem3nt in the so-cllled GPIB
pro~ram since bus 14101 is Pres1med to implement the GPIB
protocol. A messag3 buffer is obtained from the OS~ and the OUTPUr DRIVER - OUTPUT BUEFER interf~~2 is arrlnged for message transmission or reception~ Task 2 then 3~ celin~uish3s c~ntr~l of the CPU.
Since Task 3 is READY to RUN, the SCHEDULER
orogram sets up the CPU to exec~te in the stack environ~ent of Task 3. In FIG. 7, Task 3 may be identified with ADNI~ISTR~TION task 11407~ The instru_ti~n, of Task 3 ~all OS to arrange for ~S to schedule an execution of the so--alled ADMIN pr~gr~m only when _ert~in events 3ccur.
Task 3 also arranges for a timeout o~ about 15 seconds to 3t73~

,~hedule the ADMIN ~rosram for execution~ ADMIN resets a timer whsnever timeout occurs. If this ti~-r signal is not reset in this m~nner, the tier 1 device 1401 is considered to have l~st its sanity and a RESET ~f the ~icc~c~utec ~_-urs upon expirltion of the timer interv~l.
As su~ested above, the t~sk numbsrs indicate the order of priority in execution, with Task ~ having the hi~hest pcioritY qnd Task 3 the lowest. The execution of tasks in the sa~uence described above presumes no external event interrupted the progressi~n through task executi~ns, and the time di gr~m in t~e top ha1f of FIG. 10 depicts auch a se3uence. It is possible, h~wever, to hlve ~n external event interruPt the top-down sequencin~. For instance, if dqta link 9201 had a messaqe t~ send in the DOWN direction prior to the execution of Task 3, then r~sk O would execute before Task 3 even exe_uted f~c the first time.
As an exa~21e de~nstcati~ extern~l event interrupts and one that is exemplary of the typical ~pe~ation ~f a tier 1 deVi~e, it is suP~osei that the four tasks dis_ussel in the above ex~mple have R'JN qnd the OS is in the state of awaiting the posting of a flag to indicate ~ task is READY to RUN (iOe., the rightmost state in the top diagram of FIGo 10) ~ It ia futher ,up?~se~ ~ ~essa~e is no~ re^eived over data link 3201 for trans~ission to LTS 161 (E'IG~ 3) ~ ~ith referen-e to the b~tto~ time diagram of FIG~ 10 and the numerals associate with the v~rious periods of execution of the individ~al task,, the following sequencing occurs:
( 1 ) A ~essage is re-eivei over lat~
link 9201 or 'O', and INPUr DRIVER 11401 signals OS that Task O should exe_ute.
(2) Task O begins to execute to verify the message via the hiqh l~vel pr~t~c~l acceptance technique.
(3) At interrupt level, ~ mess~e is receive~ across bus 14101. Task 2 is m~de ~93~737 - 32 ~
READY to ~UN, but execution is precluded until Task 0 relinquishQs _ontrol of the CRU. The massa~e on bus 1~101 is headel UP
the hierarchY, say over link 9202.

(4) ~t the completi~n of the ve~if~~ati~n phase anl message rec~Ption by T~sk 0, the message is sent to ~ask 2 sinca the 'down_circuit_type' field in the HE~DER
inlicated a LTS was the ultim~t3 message destinationu During this interval, the OS
SCHEDULER begins execution. N~w Ta~k 2 has the highest ~ri~rity th~t is in the RE~DY
to RVN state, and c~ntr~l i, pa,~ed t~
Task 2.

(5) Task 2 procasses th2 messaqe sent to it by Task 0, and begins sendin~ output ovec GPIB bus 14101 to the tiec 2 interface indicatel in th3 'd~wn_routa' ~ield of HEADER. Now the me~s~g~ pcevi~,ly received for UP direction transmission may be Processed by Task 2 bef~re r~lin~uishing control of the CP~. A signal is sent so that Task 1 may be made READY t~ RUN, and ` control is Passed to OS.
~6) The SC~EDULER sees that Ta,k 1 is the hi~hest priority task that is READY to RU~, and passes -ontrol t~ T~sk 1.
~7) Task 1 processes the message available through Task 2 ~nd sends the message, properly formatted, over da~a lin~ 9202 Control is passed back to 0~l (8) The output previously initi~ted over ~u, 14101 i, n~w co~plet2l so T~sk 2 is made READY to RUN and 0~ passes control to Ta,k 2.
~9) Task 2 effe~ts follow-uP pr~cessing :: by freeing the ~ess~ge buffer f~r u;e .

:~l9~7~7 _ 33 -elsewhere by the microcom~uter ~nd relinquish2s control of the CPU.
(10) ~o task is ~resently READY to RU~
until the interru~t handle~ fo~ data link '1', via I~PUT DRIVER 114~1, si~nals ~S that tr~nsmission UP link '1' is now complete, wher-lP~n Task 1 ~hou~l ba executed. ~ontrol is Passed to Task 1L
(11) Tas~ 1 perf~rms cle~n-up o~.~rati~ns for its recent transmission ov~r d~ta link '1'. OS is ag~in given contr~l.
(12) The SCHEDUL~R continues to execute until another I~O activity in the microcomputer indicates that a Particular ta,k should ~UN.

By way of a shorthand not~tion, whi~h is similar to the actual high-level lan~ua~e utilized ~o Qc~gram the tasks, the routin3 algorithms realized in device 1401 may be summarized as f~llows:
(i) Routing Al~orithm for Task O and Task 1:
ir ('down_circuit_tY~e' = D~N 1){
pass messa~e to local ADMINI~rRATION
task;

else { dsstination = bits 6, 7, 8 ~nd 9 of '~own_roote';
set 'u~ route' bits 4 and 5;
pass ~es,age to P~RALLEL OUrPUT
task;
}
~ii) Ronting Alg~rithm f~r T~sk 2:
if ('up_circuit_type' = DC~.1_1){
pass moss~e to lo~al ~DMINIS~RA~ION
task;
- 35 }
el,e { if ('up_rout~' bits 4, 5 = 00 {

3'~37 pas, me,,~g3 t~ SERIAL DATA O;
}

els2 { pass message to ~ERI~L
DATA 1;
}
}

In each of these coutinq algocith~s, the ,ymb~lic notltion DCN_1 has been utilized. ~s alluded to earlier in this sectiont gene~atocs of mes;age, can inlic~te n~t onlY
the destination ('down_route' and 'up_route') but also the microcomputer tyE~ within the hierarchy of the MLT ,ystem.
DCN_1 is one type ~nd rsfers to tier 1 devi-es of DC~N 1400 ~ther types thqt may be referenced in byte3 ~down_circuit_tYpe~ or 'up_circuit_type' includa: MLT_GNTLER for FE com~uter 22~ oc 221; DCN_2 for tier 2 interfzces and DC~_3 for tier 3 circuits of DCN 140;
LTS_CNTLER for the LTS controll3r, PORT_CN~LER for Port controller and PMU CNTLER for precision measurement unit _ontroller, these latter three ^ontrollers are found in LTS 150 or 161.
~ s inlicated in Sacti~n 2.la with ref~ren-e to FIG. 4, the busses serving as inputs to and outputs from connecting arrays 141 144, as uall qs the ~rray bus,es themselves, implement the GPI~ protocol. aimil~rly, the input and output busses associated with matri~ 145 ~tilize the GPIB proto-ol. In the ~ase of an array 141,..., or 144, it is evident from FIG. 4 that each tier 1 device _ontrols an output GPIB bus that has twelve talker~listener,, For inst~nce, bus 14101 is controlled by tier 1 device 1401 and the twelve T/L networks on ~us 14101 sarve as inputs to interfaces 1421-1432, re~pectively.
'~ithin thi; GPIB f~amework, it is na-essary to provide ~n embedded ~rotocol for connecting a plurality of T/L
networks to a _~ntroller on th~ -ame GPI3 bus ,o that ~essages ~ay be transmitte~ efficiently anl message oYerhead is mitigated in return of message qccept/~eject ~93'73'7 status inf~rmation. The D~ rticular PARALLEL OUr?Ur task and the associated P~RALLEL IN~UT t~sk ac_o~plished the embedded protoc~l. Furthec dis_usssion of thi~ ,ec~nd-lsvel Protocol is hald in abeyance until v2IB -ircuitry and software ~re presented.
2.2 Loo~ ~es_ln~_~Y_tem ~LrS2 2 D 2a Stru_tur_ Referring again to FIG. 2, it is shown pictorially th~t wire-center ba,ed LrS 160 (LTS 151 is substanti~lly the same) Performs communication, loop access ~nd loop testin~ functions. Lr~ 16~ is actually an ~rrangement of loosely coupled microProcessors organized to ~erform these functions. The term "loosely coupled" i5 used herein to lenote an organization of pr~cessors that sh~re no _ommon memory but communicate by p~ssing messages over serial or 2arallel oriente~ ch~nnels.
FIG. 11 shows a block dia~ram of LTS 150. LTS
-ontr~ller 2000 is responsible for communications witn DCN 140 (FIG. 2), via seri~l d~ta link 930, and for loc 1 control of other Lr~ subcomponents, including: pre-isi~n ~e~surement unit (PMU) ~101, 2102 and 2103; port controller 2200; t lk circuits 2301 thr~ugh 23Q5; direct distance dialer (DDD) circuit 2~00, ringing distributoc 2500; qnd ~orti~ns ~f e~uipment ac-ess netw~rk 2S (EAN) 2700. Each ~f these subcomponents is explained as the discussion proceeds.
LrS -ontroller 2000 and Port controller 2200 are linked with intsrconnect bus 20001, whi~h typi~ally supports a parallel-oriented protocol such ~s the GPIB~
~o~t ~ontroller 2200 is res~onsible for tha loo~ ac-ess function in that it provides tip, ring and sleeve _ontrol for connections to so-called "n~-te,t" tcunks 340 that enable the MLT syste~ to inter~ce to switching machine 170 (FIG~ 2~. A no-te,t trunk is ~ne th~t Qrovides the ability to in~erconnect to an~ customer line 180 or 181 in a bridging ~ode. One such test trunk is shown a, rIP 1 2ING 1 Pair 9401 with its -orresPonding sle2ve lead S1 ~1~3'7~
36 ~
le~d 9417 in FIG, 11.
P~U's 2101 through 2103 are also interconnected to LTS controller with bus 20001. Each ~MU 2101, 2102 or 2103 is a general purposs testing circuit that is used to ~ake measurements on customer lOOpa 180 and 1~1. E~ch LTS 160 may contain from one to three PiY~s~ The maximum nuDbec is dspicted in FIG. 11. PMU 2101 (PMU 2102 or 21~3 is simil~r) accesses a customer loop 180 or 181 through a serial arr~ngement comprising, for example~ e Pair 21010 emanating from PMU 2101; 2qui~ment access network 2700; wire pair 28010 serving as the input to port device 2801; and p~rt device 2801, which is ~n interface to no test trunk p ir 9401. EAN 2700 serves to interconnect any P~U 2101, 2102 or 2103 to any port devi_e 2801, ~.. or 2816 under contco1 of both LTS _ontroller 2000, via bus 20~02, and port controller 2200, via bu, 22001. The ~ONTROL ~701 portion of E~N 2700 connects to bus 20002, ~here~s the P ~N~L 2702 Dort~on ~f ER~ 2700 -~nnects to bus ~2001.
LTS c~ntroller 2000, port controller 2200 and PMUs 2101 throu~h 2103 are sach self-contained microprocessor modules. Because of the rel~tiva in~epenlen-e of these microProcessor modules, the MLT
system is modul~r so that wire _enters (150 or 151 of ~5 FI~. 2) r~ngin3 from one thousand to one hundred thousand -ustomer looPs can be served by au~menting the basi-,ystem. rhus, ~s a wire center grovs, more PMUs can be ~ddad (up to three per LTS), up to sixteen port cir_uits -~n be ac~ommod~ted (the ~aximum of sixteen is shown in FIG. 11 as circ~it; 2901 through 2815~, ani EAN 2700 can be expanded. Hance the largest size L~S can h ve up to ;ixteen loops simult~neously ac-essed for testing and _ n time share three identical P~Us to Perform requeste~ tests.
~he separ~tion of the testing function, acc2ss function and communication fun-tion allows for ths simultaneous operation of these functions~ thereby m~ximizin~ th~oughput rOr a ~iven testing traffic load.

. ~ .

'7~'~
~ 37 2.2b LTS_O~e~_ti~n Wi~h reference to FIG. 11, LT~ -ontroller ~000 i~ple~ents a serial-oriente~ Pr~toc~l f~nction ~n incoming data link 330. Re~eived m2as~g2s, in the form shown in o ~IG. S, ~re Parsed to obtain the INFORMATION fi~ld ~s shown in FIv. 5, and then interpceted in L~S controller 2300. An ~ccess re~uest is typically the first messaae received, as indicated in the 'down_task_id' byte of the HE~DER by the binary equi~alent of ACCESS and in the 'request response' byte as RE~UESr in binary rapre-aentation. rhis messa~e -auses LT~ contcoller 2000 to initi lize an area ~f its RAM
to track and time the request as well as to generate a ~acallel~proto^~l ~essa~e f~r P~ss~e over bus 20001 t,o port controller ~200. The informati~n utilized to ~onstcuct this latter messa~e is fo~nd in the DATA ~ortion of the INFORMATION field of FIG. ~. For inst~n-e, the .irst byte (byte 1) may be, symboli_ally, '~CC~OTE~T .
This indicates th~t the ty22 of ac_oss ~esired is a -onnection to a "n~-test" tcunk. An~thar byte ~oull indic~te the 'switch_type' to inform ~ort controller 2200 of the type of switchin~ ma-hina (e.g., an electronic central office or a cross-bar office)4 The next several byt~s list the telaphone number OI the customer loop to be accessed. Based on message content, ~ort controller 2~Q0 proceeds to access the loop spe-ified in the m2asasa by ~ttaching trunk di~ler 2650 (see FI~. 11) to a free ~ort 2~01 throu~h 2816, dialing the telephone number, and attaching busy/spee-h detector 2600 to determine wnethec tha loop is idl~.
Presumin~ loop a^-sss is obtained, ~ort -ontroller 2200 sends a resoonse acr~ss GPIB 2~01. This response proceeds in the UP diraction and, ~ccordin~ly, appropriate INF0RMArION field bytes must be filled. I~ith referenc2 to FIv. 6, the 'request_rssponse' Dyta h~s the antry ~SP0NSE in binar~ ~rm placed in the HE~DER~ In the DATA porti~n, byte 1 has an ent~y tiat 2ch~s tna test c~de which, in this case, is 'ACC_~OrEST'. ~his is to indicate , :~93737 that the completed request ~onforms to Ihe desired reques~.
~he secon~ byte (byte 2) in~icate~ the 'st~tus' of the re~uest and the third byte (byte 3) indicates the 'port number'. For the instant examPle, these bytes might re4d, sYmbolic~lly ~s 'ACC_COMPLE~E' and 'P~RT_1' to indicate that port 2801 of FIG. 11 h4s ~ connection Pstablished to the loop ass~ciated ~ith the tele~hone numbec sent in the DOWN direction.
At this point in the o~eration, the loop is 4ccessed, 4nd LrS 160 awaits subsequent ce~oests, typically to effect testin~. ~ost te,t re~uests require the ,ervices of one PMU 2101, 2102 or 2103. However, some re~uests can be satisfied by either LTS _ontcoller 2000 or Qort controller 2200 and their associated circuitry. Test re~uests ace c~de~ ~o that LTS _ontr~112r 2~00 -4n ~etermine which L~S circuits can satisfy the re~uest. LTS
contcollec 2000 therefore a-ts ~s a resour^e mana~er foc the entire Lra 160.
In order to Droceed with the oDer4ti~nal iescription of LTa 160, it is necessary to discuss its componant part, in ,ome detail. Attention is focussed first on LTS controller 200~, followed by p~rt -ontr~ller 2200 and PMU 2101 an~, fi~ally, the remaining circuitry of L~a 160 shown in FIG. 11 2~201 LT~_Coa_roller LrS ~ontroller 2000 is a microcomP~ter-ba,ed system also runnin~ under the same operating sys~em ~OS) as DCN 140. ~gain, the soft~are controlling the nicro20mputer is pactitioned into tasks, ~nd task, conmunicate with e~ch other by signaling each oth~r or by sen ing messages to one ~nother vi~ fa-ilities provided by OS. In LTS
_ontrollec 2000, the tasks are as follows:
(a) aERIAL DATA task control, d~ta link 930 and implements a high level data link protocol ~n all messa~2s passing onto oc co,ning fro,n phy,ical data link 330. All tasks that must transmit ~ata over link 930 do so by sending the data as a message to the SERIAL DA~A ta,k.

3~7~t7 ~his task is oquiv~lent to the ~ERIAL DA~A task 114014 o FIG, 9 asaociatad with DCN 140. ~ll meas~ges entering LTa 1~0 and destined for a s~ecific task in LTS
controller 2000 muat pass throu~h SERIAL DA~A.
(b) PAR~LLEL DATA task controls the transmission and recePtion of messa~es over ~arallel-oriented bus 20001 shown in FIG. 11 All tasks thqt muat tranamit datq over bua 20001 to port _~ntrol1ec 22~0 ~r to PMU's 2101-2103 do aO by sending the data as ~ mesaage to the PARALLEL DATA
taskO Si~ilarly, data received fro~ controllec 2200 or units 2101-2103 Pass through the PARALLEL D~TA task. This task is e~aiYalent to tha PARALLEL OUTPU~ tqsk 11407 of FIG. 7 associated with D~N 140.
(c) ACC task Pro-esses re~uests for ~cceas to trunk~ 9401 through 9416 of FIG. 11 anl re~uests for establishment of callback paths via the nationql dicect distance dialin3 (DDD) net~ork ~s i~plemented by DDD
~ircuit 2400. Tho processing of reguestâ f~r l~o~ qcce-as includes the formatting of mess~ges to port controllec 2~00, ~here the ~cceas ia actually ~erformed, and the setting up of a timeout over the ac_ess activitv in port controller 2200. The ~CC task indicectly ~enda a messqge for loop a~cess to ~ort controller 2200 by sending the message to the PARALLEL DAT~ taak. Re~esta to DDD
circuit 2400 are transmitted over bus 20002.
(d) rs~ task controla the pr~cesain~ of test requests on a given Port, selected from one of the ~octs 2801 through 2816, once that port has accesaed a loo2 for testin~. There are sixteen TST tasks, one for each ~ossibls port 2801, ..~, 2816. The TST tasks are not bound to a parti~ulac p~rt number in ~ fixed manner, ~ut may be assi~ned to any inlividual port 2801-2816 over ~ long period of time. For example, for the ducation ~f a given loop access, TST 7 task may be ~ssigned to port 2803. When the accesa to ~rt 2803 is drop?ed~ TST 7 t~sk may be ~ssigned to port ~801. ~nce the assignment is made, it is fixed for the d~ration of the loop ~CCeaS~ Thia dynamic ~37;~7 ~ssignment ~llo~s processin~ priority t~ be evenly distributed among ~orts 2801-28~6. TST ta,k s~ftware eithec performs the test re~uest it,elf or ~rran~es for the test to be performed by either port controller 2200 or PMU's 2101-2103. TST task also provides ~ time~ut function or the re~uest.
~ e) rCD task controls the di~ling for talk circuits 2301-2306. This task -an ~ani~ul~te D3D
circuit 2400 and thereby arran~e a callback to, typically, a craftsperson qt the facility iesi~nat~d tne M~intenan_e Center which contains the I/O terminals 230,231. The _~llblck fea~ure is requirei to imPlement the combined talk/test procelures of the MLr system whereby a _r~ftsperson can be in speech communication with either a ~usto~er or another crafts~erson over a loop accessed for testin3. rhe mq~inte~ance qlministr_tor at the ~aintenance Center can enter a test re~uest as a ~Lr sy,teD u,ec, have that test run by LrS 160 while the talk path is broken, and when the te,t is c~mpleted, hav3 th3 t~lk ~ath ces~red by 20 LrS 160. rhese are two TCD tasks in ~T~ controller 2000 s~ft~are a~ that tw~ dialin3 operations mqy be _onc~rrently in Progress.
(f) ADMINISTRATI~N tqsk provide~ all llministrqtive functions in LTS 2003~ rhese func~ions 25 include: ,ending t~ FE com~uter 220 or 221 a request for ~ata base download when LTS 160 is reset an~ processing thi~ lownl~aded datq bqse; cesp~nding t~ e_ho messa~es from ADMINISTRATION task of DC~ 140; and ~roviding qn interface during self-dia~nostic checking.
(g) DIAGNOSTICS task provides self-testing capa~ilities that are used to dia3n~se LrS -ontr3ll~r 2000 hardw~re problems. DIAGNOSrICS task interf~ces to ADNINISTRArION task, via tha O~ messqge P~s,in~ facility, to request and receive the rese~vation ~f LrS 150 h~rdware for use in conducting self-~est~.
(h) DU~P MEM task arranges for the transmission of a snapshot of LrS contr~ller 2000 me~ory when a -373'~

malfunction occurs, At syste~ startup or ~hen a system re,et ~ccurs, operating syste~ OS initializes its tables, pl~ces ~ll ~essage b~ffec, on a "free ~ueue" ~f bufEec,, initillizes all syste~ semsDhores or inter-task si~nals, an~ makes each task READY to execute (~UN). The Oa then c~lls a hardw~re ~nd software initialization fun-tion. r~bles ace kePt in ~ecmanent memory and define the state of the e~lip,nent conflguration to be associated with the~ Particular LTS 160.
For instance, the number of PMU's 21~1-21~3 confi~uring the particular ~T system is one such t ble Parameter. These tables are accessel for initialization. ~ext, the task scheduling function, again called the SCHEDULER~ is axacuted. Program execution in LTS 160 is similar to that ~f the DCN 140 ~nce the SCHEDULER is called. rhus, execution is transferred from the S_~EDULER to the highest pri~rity t~sk which is READY to RUN. At ,t~rtup, all ~asks are READY, and the SERIAL D~TA task has the hi~hest QriorityO Executi~n of SERIAL DATA enable, the ha.lware ~0 receiver associated with link 930 and causes a transmission ~f a data link ,tart-up me,,age to DCN 140 in the high level protocol format. The SERIAL D~TA task then relin~uishea ~~ntrol of the CPU in L~a contcoller 2300, The OS is now free to select another task f~r exe~ution.
rhe P~RALLEL DATA taak has the ne~t highe;t priority and executas so as to enable its associated hardware for two-way communication on bas 2~001. C~ntr~l is again passed to the 3S once the task is initialized.
All th~ ~ther tasks eventually RU~ an~ initialize themselves and their associ~ed hardware. rhe tasks then ~wait some activity requiring their spe~ialized services.
Usually they wait t~ reseive a Dessa~e buff~r ~c f~r a sema2h3re to be poste~. It may also be that a particul~r task is w~iting f~c a time~t t~ oc~ur bef~re cegaining control of the CPU. For examPle, ADMINIS~RATI~N waits for ~bout seven sec~nd, be4Ore ~aining c~ntcol lftec it~
initi~lization; this task then sends a data base downlo~d .. .

~37~'~
_ 42 -ce~uest to FE c~mputer 220 or 221 by passin3 th~ message to aERIAL D~rA for transmission over d~ta link 930.
The ~ownload data messages from FE computer 220 or 221 pass thcough the SERIAL DATAL ta~k ~nd qre routed ~ccordingly to lata in the TNFORMATION fiel~. Down~oad messages h~ ~9 L~S_CNTLER (Lrs controller) n~mes in 'down_circuit_type' ~yte anl ADMINI~rRA~IO~ task in the 'do~n_task_id' byte. Conse~uentlY, the routin3 fun-tion in LTS controller 2000 reali~es th~t the INFOR~ATI~N field is to be processed in LTS contcoll~r 2000 itself ~nd sends the message, via Oa, to ADMINISrRA~ION task. This task or~cesses the m2ss~ge by p~sin3 the data that ~ppears in the DATA portion of the message, Do~nload mess~ges identify the number of ~quipment types inst~lled at the Particular LTS 160 site and the ~resent status of the eguipment (AVAILA8LE, OUT_~F_SER~ICE, ~nd ,o f~rth), These messages ~lso organize ports 2801-2816 into trun~ groups, s2ecifY di~ler types associ3ted with talk _ircuit 2301-230~, and so on. After configurati~n information h~ been lownloaded, Lr~ 160 is ~rep~red to process ~ccess and test requests.
2.2~1a Ac~es__Re~uest Vro__s_in~
Access request messages ha~e LTS controller 2000 s~ecified in the 'down_cir_uit_type' of the message header symbolically as LTS_CNTLER and the ACC task in the 'down_tas~_id' symbolically as ~CC. The SERIAL DATA task couting function tcansmits the ~ccess mess~e to the ACC
task.
rhe ~ormat of the DAT~ portion of the INFORMATION
3~ field of FIG. 5 has two ~os,ible arrangements depen~ing on the type of access desired. Four types of ~ccess ~re ~llowed:
(i) a regular test access of customer loop 180, ..., 183; tha INFORMATION -Cield is exempli~ied in FIG. 12;
(ii) a main distribution frame (~DF) trunk access 3s also exemplified by 37.~7 - ~3 -FIGo 12, (iii) a regular tsst access plu~ a c~llba~k t~ the Maintenan~a Centar; the INEORM~TI~N fiald is exemplified in FIG. 13; and (iv) a callDack of ~he Mainten~nce Center that is to be ? sso_iated with a specified test acc~ss alreadY in effsct at LrS 160 site, FIGo 13 also depicta the corrasPonding INFORMATION field.
Processin~ for each of thesa types of a_cess is covered next.
2.2.1a.1 ~esul_E_E s _Acces___nd_~DF_rEUn__Ac-ess Regular test acces~ c~quires that ~ir-uitry and equipment ~ithin s~itching machine 170 be m?nipulated ac~3rding to the type of centr~l office (e.~, ~ross-bar or electronic). ~DF trunk access requires only th~t local msmory tables be up~ate~ ~ith entriea discl~sin~, in effect, that the trunk circuit is being attended to by ~raft per,~nnel. MDF trunk; ar3 n~t ~utom~ti_~LlY
connected to ~ ~ustomer looP, but require intecaction and manipulation by a -rafts~e~son located ~t the M~F.
The ACC t~sk begins to RUN when a message is sent to ito In the i.mmadiate case, the measase is a RE2UEST for aither a test trunk or ~DF trunk ac_ess. A memory tablq is used to store pertinent information about the REQUEaT; such inf~rmati~n i~_ludas the a~ress of the RE~JESr messaqe, memory lo_~ti~ns for the stora~a of the address of a RESPONSE me,sage, and whether a callback i~ re~uired for this REQUEST. rha access code (regular, desi~n~ted by-~OTESr acceaa, ~r MDF acces;), the swit-hin3 ma~hina tyPe, the trunk ~roup c~ntai~ing the loop under test and the tslephons numbec of the customec are ~l~ced as data in the message buffer. ~he address of the ori~inal RE~UESr message and the address o4 the table used t~ ,t~e information about the REQUEST are also placed in the message HEADER, in the 'uP_1Par~met2r' ~n~ ~u3_2Par~meter~

, . ~
, 373'7 -- ~4 --lo_~tions~ so that the res~-.se of oort con~r31le! 2200 can be identified with the present RE~UE~ he messa~e is - then ,ent to PA~ALLEL DATA ta,k for tranami,si~n to port _ontroller 22~0. ~ timeout is started on the activity of port -ontroller 2200 and ACC task relinquishes control of the CPU.
When port controller 2200 _om~letes its pro_essin~ of the access re~uest, it returna a RESP~SE
message to ACC task by sanding the message cross the P~RALLEL D~TA task. ACC taak i, id3ntified in the 'up_route' of the message HE~DE~ and the routin~ unction in PARhLLEL DArA t~sk sends the message to ACC task. ACC
task ~ssociates the RESP~NSE message with the ~riginal rs~uest measage by checkin~ for the address of the original ce~uest mesaa~e anl of the temp~rary st~r~e t~ble used for the request. rhe ccess response message h~s the foriDat aho~n in FIC. 14. ~he 'status' byte iniicates ~hether the ~ccess was successful or not~ If it was unsuc_assful or i LTS controller 2000 had timed o~t on port contr~llec 2200 re~uest, a RESP~NSE message is formed and sent to SERIAL
D~A task for transmissio~ UP the hierarchy. The temporary table use~ to store d~ta for the failed request is now made available for use with a~other ~ccess REQU~ that may have arrivedO
If port ~ontroller 22~0 passe, a RESPONSE that indicates an ac_ess has been obtained, ACC task atte~Pts to _lose a relay eDbedded within e~uipDent ac-ess network (EAN) 2700 tFIG. 11) to one of tha ports 2801-2816 selected for loop ~-cess, If this opsr~tion fails, trouble counters ~re stroked against the selected port 2~01-2816 and EAN 2700 ~nd the aforementione~ failure se3uence is folloWed ~gain. If relay closure is su_cessful, ~CC task selects an idle T~r task to control testing on the sele-te~
port, arranges to have a meDory spa~e c~lled the port ~ontrol table fillsd with infor~ation about tha access~ and makes the chosen TSr task READY to exec~te~ Po~t c~n~r~l table information includes the address of the original 3~7~37 -- 4~

request message, the address of the results buffer received from port ~ontr~ller 2200, whether the access is of long or ,hort hollin~ time, a timeout v~lue to be used to timeout the access before it is autom~ticallY dro~pad, the logical identifier of the FE c~mputar t~at ~a~uast~l th2 a--ess, ~nd an identifier that allows the FE computer t~ associ~te the ac_es, with a results b~ffe. intern~l t~ the FE
com~uter. ACC task is now finished with its processing of this acce,s re3uest~ and makes its temp~rary table available for use with a new ac-ess request. rhe return of a RESPONSE me,,~ge is the c2sp~sibility ~f the ~sr task, and will be covered in a later section. This convention ha, been a~t2d because tha origin~l RE~UE~T messa~e maY
have a test RE~UES~ aPp~nded to the access REQUEST.
2.2.~.2 In__E_ct _e--cce---Regue-t-pEQcessi~g rne interactive a_ces, re~uest me,sa~e of FIG. 13 is used when a loop access is desired together T~ith a talk ~ath to a craft,person in the M~intananoe ~enter. ~he re~uest message format is bqsically the sam2 one usad for a regul~r test ac_ess, as per FI~. 12, except that a callback telephone informat.i~n has baen ~ppend~d anl the 'request_c~de' is symbolic~lly ~esi~nated ~C_INTR (as _ontrasted to ~CC_NOTEST or ACC_MDF of FIG. 12)~ ~he ACC
task processes the so-called "regular loop portion' of the message as outlined above. Ho~2Yer, be,ide~ f~cmatting and sending a messa~e to port controller 2200, q message is ~lso ,ent t~ one ~f the TCD ta,~s. This l~tt~r message contains the callback telephone number apPe~rin~ in the ~riginal D~WN r~ute REQrJ~ST message as is shown in ~I5. 150 ~he ACC task now waits to receive two RESPONSE mess~ges, n~mely, one fro~ port controller 2200 and one internally from ~CD ta,k. A timeout is startei on these ~-tivities~
rhe TCD task starts to RUN as s~n as it can be ~cheduled a~tec ACC task relin~uish2, c~ntcol ~f the C?U.
rCD task receives messages sent to it a~d ba~ins to execute its dialing algorithm. The task als~ atte~ts to a~~uice one of talk cir~uits 2301-2306. I~ no cir~uit 2301-2306 is l9~3'i'~'7 ~vailable, the callback se~uencP fails and ~ message to this 2ffe-t is sent to ACC task. If one of the circuits 2301-2306 is avail~ble, ~CD task ~ttempts to acluice either a dial pulse dialer ~r in-band iialec for use with the av~ ble talk cir~uit. ~he ~ialer is represented in FIG. 11 by DDD circuit 2400. The di~ler type depen~s on the central office e~uipment used to terminate the talk circuit, whi-h aQPears to the cantral office switching machine as a st~tion set on a customer loop. The dialer type is ~ ~ar~meter cont~ined in the download data sent from the FE ^omputer to LTS 160 as part ~f the st~rtup ,equence dis-uss2d above~ If there is no ~ialer circuit 2400 available, aith~r b2cause it is presently in use or out of service, the cal~back se~uence is termin~ted, the selected talk circuit is released and made available for use on anoth~r _~llb~_k ~e~uest, and a failure massage is sent to ~CC task.
If dialer circuit 240~ is ~c~uirel, the callback di~its D1, D2, ..., D12 are passed to a di~ling pro~ram, ~nd the digits are dialed. The dialin~ oc-~r~ at the interrupt level since dialin~ t kes between 1 ~nd 10 seconds to c~p1ete and, c~nae~u~ntly, rCD t~sk 3ives uP
control of the CPU for tne dialing interval at leastO ~hen ~ialing i, complete, an interruPt h~ndler post, a semaphore to signal ~CD task that it should return an~ continue its processin~. Before having relinquished control of the CPU, rCD task started a timeout on the dialing a_tivity. If this timeout expires before notific~tion of di~l -ompletion, TCD task arranges to free its associate~
e~uipment, namely, one of the t~lk _ircuits 23~1-2306 and ~ialer 2400, and generates ~ failure message for PCC task.
If ~i~ling successfully completes, T~D task frees dialer 2400 cic-uitcy, and enables the ~ at2~ t~lk circuit ~301-2306 for the de~ection of a handshake sign l -alle~ "KEY-~ER0". The craftsperson at the Maintenqnce Center is required to depress the "~" kaY on th2 in-band signaling pad ~f the teleph~ne ,et to signal L~S 160 that ~L93'737 the callback h?, bsen succe,sfully ceceived at the t1aintenance Center. The TCD task starts a timaout for the ceception of the KEY-ZERO signal by the talk ci~cuit h~r1ware, ~nd if ths timeout ex~ires before the signal is received, tne -allback is ?borted, ?nd the failure procedure outlined above ia initi~te~. If the KEY-ZER~
signal is detected by the talk circuit, the callback ae~uence ia c~pletad, and ?n indic?tion of thia i5 formatted and returned to ACC t?sk. The messa~e contains inform?tion identifying the tal~ circuit 23~1, ..., or 2306 utilized.
rhe ACC ~ask can ~eceive RESPONSE mesaagea from ~CD task and port controller 2200 in either order since the ~ctivities of -~1lback and loop access are ~synchronous with rss2ect to each other. After both responses arrive, ~CC tas~ c~mpletes its Proc~ssing of the a_-e-aa re~llest by checking 'status' results and either sendin~ a message to FE computer 220,221 or by conne~tin~ ths ~llo_~ted Qort from pocts 2801-2816 and the selected talk circuit from 2~ -ircuits 2301-2306 through EAN 2700. If the loop a-cess failed, or if the ~ttempt to connect the alloc~ted port f~ils~ a failure message is returned to the corresponding FE computer, and LTS 160 e~uiPment on ths f?iled ~rrangement is relinquished. If the connect attempt fails foc the allocatad talk circuit, the talk circuit equipment is freed, trouble _ounters ?re ,trohed, an~ a r~T task is aelected foc loop access in the manner ~es~!ibed ab~ve. If the callback attemPt is suc_essful, the loop access is successful, and the connection throu3h EA~ 2700 i~
successful, a ~T task is selected to oversee testin~ on ~hs loop, ?nd ACC t~sk comple~es its Proces-aing with basically the same procedure as des_ribed aboVs for the "loop accsss only" case.
2.2.1~.3 _a~ c__A~ oe-sing rhere a~e instances wnen ~ ~inten?n-e Center ?dministr?tor needs to talk to either a customer or to an outside rePair per,on after the customec lo~p h~s been 1193'73'~

successfully ac_es~el for tssti~g. In thes2 instan_es, L~ 160 receives basicallY the same mesaage of FIG. 13 ~x^ept th~t tha 'ra~uest_~ole' is, symb~lic~lly, AC~DDD
~nd the p~ct 23~1-2816 to ba associ~ted with the call~ack in the 'down_Parameter' bYte of the HEADER.
~ he A~C task begins t~ execute when thi, nes,~ge is received. It formats a mess~ge for r~D task as outlined above for the interactive tPst -ase, senls the mess~ge and w~its for ~ REaPONaE. A timeout is started to time the 1~ c~llback ce~uest. rhe TCD task ~ro_esses this ~nes,~ge exactly as described above, and returns its response to ACC
task. No mess~e from port controller 2200 is expected in this case, so ACC task proceeds to send a message to the FE
^omputer ~ssociated with the AC~ESS re~uest or to attach ~ne of talk cir-uits 2301-2306 to the specified port, iepending on tha 'status' raturned from the callback activity.
rhe descri~tion t this e~int in this secti~n has covered in some detail the action of ACC t~sk and rCD task~
It should be re-alled that these soft~ace f~nction~ operate in a multitasking environment, and that at anY instant, ACC
task can be pc3~essing several ~ccess re~uests that are in different states of comPletion. However, TCD tqsk is lesign~d to pro^ess one dialing request at ~ time. To insure efficient thcoughput, there ~re two rCD task~ within the software of ea_h ~TS controller 2~bO. Consequently, tw~ dialin~ activities can be g~ing ~n in LrS
contr~ller 2000 c~ncurrentlyO Sin_a there ~re two dialer types, nanely, dial Pulse and an in bana, in L~a 160 f~r dialing ovar the national tele~hone network, two ~CD tasks insure~ that ,naximnn dialin~ a-tivity m~y o_su~.
2.2.1b Tes__ReaUes--~ro~QsslBg ~ n a-tive TST task ha, a Priv~te mem~ry t~ble that it ~ses to control testing on ~ given port. En~rias in this tible include the aldress for a request message or addresses f~r a se~ies of massa~es ~nd the -orresponding ~ddress or addrasses for tha responses. TST task i5 first ~3~'7 activated by the a~tion of ACC task, which ~tt~ches both a ce~uest b~ffec ~nd a response b~ffa~ to the t~ble. Then ~sr task bsgins a timeout of the loop acces,; if the timeout expires before the loop access is dropped by ce~uest, the l~p ~ccess i~ automati~ally droppad by LT~
-ontroller 2000. ~his timecut ~revents the loss of use of LrS 160 ciccuitry such as t~lk -ircuits 23~1-2306 ~d ~orts 2801-2816 in cases where FE computer 22n or 221 failures ~ccuc. One of the re~1est, th~t _~n ~e made of ~sr task is that of restarting the timeout activity on a lo~p undec test so that any accsss may be held for 1onger than the initial timeout value if reguired.
After initiating the timeout qctivity on loo~
~ccess, T~T task processes any reauest mess~ge in the table ~s follow,. A 'cucrent cou~t' variable th~t hl, bean pre-set bY ACC task has a value eau~l to the number of bytes taken by the a~_es, request dat~. In a~dition, ea~h messa~e buffer has a field called ~nbYtes~ that contains a -ount of the number of bytes of meaningful dat~ containad in the bufEer. If 'current count' e~uals 'nbytes', the message contain3d only the ~CCE~S re~ue,t, ~nd ~ST task ~rran~es to senl the response messa~e a,sociated with the initial ACCESS reguest in the UP direction~ If, however, -urrent count is le~s than 'nbytes', then test rea~ests have been incluled with ACCESS ~equest, and TS~ task proceeds to pr~ce,, those ~ther re~uast,. rhi, pro_essing activity is described in the subsequent ~aragr phs. For each test reque,t found in the re~uest mess~ge, ~ST task arranges $or the request to be Performed~ -0ll3cts the response in tha sssociated resp~nse mes,age b~ffer, and when the last request has been processed, returns the ces~onse message to the FE computer 220 or 221 ~aking the requests. If the last request ~rocessed was not one to drop the tast a_cass, TST t~sk then waits for the arrival of a new messaga c~ntaining test requests. In this way, tha FE com~uter guiding the testing can reguest tests to be performed, analyze results ~nd 1eter~ina tha naxt tast co ~19;~7 ~e performed ~-~ording to its e~bed~ed ~daptive te,t algorithms.
~ henever the ass~-iat~d FE co~put~r 220 or 221 transmits ~ new messaqe of test request, D~WN the hierarchy for a loo~ alre~dy accessed via a Particular L~S
p~rt 2801-2816, th~t messa~e is received by the SERIAL DATA
t~sk and routed to the appropri~te rST t~sk. rhe HEADER
portion 'lown_parameter' byte c~ntains the ~rt ide~tifier, and a dYnamic t~ble in LTS -ontroller 2000 is used to ~etermine the specific TST task governin~ activity on a specific port, rhe ~ST task is s_hed~lled to RUN ~hen the new ce~uest message is sent to it. The ~ST task attaches the message to the temporary table ~eferred to ~bov~, ~nd sets 'current _ount' equal to the size of the message KEADE~.
~onse~uently, '_uccent count' h~s ths offs2t ~f the first byte after the message ~ADE~, which is the first request in the ~resent mes,age. This i, de?icted in FIGo 15~ A
message buffer is now obtained from OS, att~che~ to the t~bleO anl used to accumulate responses to the requests s~ecified in the REQUEST message~
Before pcocessin~ any test re3uests, ~ST task determinss if a DDD callback is associated with the looP
under test, If so, ths callback path is Pl~cei in the ,o-called HOLD mode so that testin~ can be Perform2d on theloop while the _allback path is still held up. The talk circuit 'mode' (either HOLD, T~LK or ~ONIT3R) is saved for restoration upon completion of test reguest processin~. In thi, ~ay, tests are ~erform2d on a loop with an ass~ciated callback, and the loop is subse~uently restored to the callback state that existed prior to receiPt of the re~uest message. The _~llback state can be changed by a reques_ in the message that ,imPly cau,e, LTS -ontcoller 2000 to -hange the value of the remembered state. When the rememberel state i, restorel, ~ new ,tate i, actually ef~ected for the callback ~ath.

~93~37 _ 51 ~ he r~T task divides test re~uest, into two _ateg~cie,, n~ly, those that _an be Performed by either LTS contr~ller 2000 or port controller 2200, and those that require the services of one PMU 2101-2103. If the reguest is to be perf~rmed by a PMU 2101-2103, rsr ta,k attem~t, to have allocated to it an idle P~U. If no PMU is av~ilable, 'status' ~f BUSY is set f~r t~e t2,t re~usst, no further processing of requests is carried out for the current re~uest me,sa~e, and the ac_umulated ce~2on~es are cetùrned to the FE comPUtsr supervisin~ the testing. If, however, a PMU is allocate~ to the TST task, a mes,age buffer is obtained from OS, the P~U request is formatte~ in this buffer, anl the buffer is sent to PPRALLEL D~T~ task for transfer to the PMU. A timeout is started on the resuest~
If the timeout expires before the PMU returns the test cesults, a time~ut failure status is re-ord3d in the results buffer, further processing of requests in the present buffer is terminate~, and the a--u~ulated r~sults are returnad to the sup/2rvising FE _o~puter~ If the ~MU
ceturns tne test results within the time li~it, the status and results data are stored in the asso~iated rasults buffer, '-urrent count' iS incremented by the n~mber of b~tes required for the just processed test, an~ TSr task determine, if the request m2ss~e contains ~nother test request. rhis determination is made by comparing '~urrent c~unt' with tha 'nbytes' ield in the re~ue~t ~essage.
~ince 'current count' is incremented with each request processed, it eventually eguals or exceeds 'nbytes', and processin~ for the present re~uest message is termin ted, ~he buffer of the accum~lated responses is ceturned to the 2roPer FE computer.
If th2 re~uest is det2rmined ~o be one that ~rs controller 2000 can respond to ~irectly, it do2s so, and ac-umulates the resPonse in the associ~ted respon~e buffer.
~5 'Current _ount' is incremented ~pro~riately. If the re~uest re~uires the services of port controller 2200, a ne~ messa~e buffer is obtained from OS, a reguest mess ~e ~93~73~
- 5~ -is formatted for Port controller 22~0, and the message is sent to PA~ALLEL DA~A task for transfer to 30rt -ontroller 2200. A timeout is initialized by P4RALLEL DATA
task, and if it expires bef~re the cesponse fr~m p~rt -ontroller ~200 is received, the timeout se~uence is executed, 2S outlined above for the timad-out P'fU raquest.
If the responsa is received within the time limit, the r~sponse buffer is updated with the results, 'current count' is incre,nented by the appropriate am~unt, and pr~cessing continues for tha next test requast, if any.
rhe ~bove discussion shows th~t ~rs -ontroller 2000 is capable of processin~ concatsnatad test re~uests re_eivad in a single raquest massage. The onlY
cestriction is that the res?on-a3s t~ all r2aueats m~lst fit into the rasponse message b~fer. ~s each ~ess~2 is ?r~cessed, ~ PMU 2101-2103 is attached to r~T t~sk, if necessary. This PMU remains asasociated with TS~ task for the durati~n of processing of the p~esent ~a~uest message~
but is fread for use by another TSr task for servicing ~n~ther l~p ac_e~aed on an~the~ port when ?r~s2ssing is comPleted for the present raguest message.
~ s menti~ned earlier, LTS 160 can bs e~uipped with u~ to sixteen ports 2801-2816 and ther_fora c~n suppQct c~ncurrent testing on sixtean lOo~a. Si~tean instances of TST task allow this processing to oc_ur, and ~a is the ~nult~tasking supp~rt for the simult~naous testing.
rhe timeout mechanisms described in the above paragcapha of this section ,erva to insure that resources of LTS 160 are not lost to the ~ystem in ca~es wheca er~ors occur. ~or ex~nple, without a timeout facility, if a P~U
sh~uld re,et in the middle ~f a test re~uest, the looP
~ccess, the associated port e~uipment anl anY associated t~lk _ircuit w~uld be permanently stuck aw~iting a resp~nse that could never o_cur. All this e~uipment would ba un~vailable to the MLT systam in the sense that it could not be used ag~in because of its permanent BUaY status.

:~93'73'7 _ 53 -he timeout facility overcomes errors of this so~t by causing ercor r~utines to execute and free ~ss~_iated e~ip~ent. ~he overall timeout on the looP access, started bY TST task as soon as loop access is com~leted, overcomes the srcor c~nditi~n that prevails ~n ~ST t~sk is ~waiting the next re~uest message for the FE computer, but that ~~mputer f~ils. Since the knowledge of the FE complter regarding accesses prior to system failure is most likely lost, the next message may never arrive. LrS 150 res~urces are likewise lost in this ~~se without the timeout mechanism because this eguipment cannot be used by ~ther FE
_~puters, or indeed, by one th~t failed and is no~ ~ack ~n-line.
2.2.1c L_~_Regues_ ~ith the Presentation of the abova ,truct~re and operation and tne introduction of certain nomen_lature, it is now appropriate to present a list ~f re~uest,, inclu~ing other access or test ty?es, processed by a ty~i~al LTS 150.
~he list shows the subsystems, that is, PNU 2101-21~3, LTS
20 controller 2000 or port controller 2200, that a_tu~llY
parforms the re~uest, and indicates the level of activity~
where a~propriate, required to respond to the request.
1. DROP ACCESS -- drop the loop test ac_ess ~nd ~lso any DDD callback associated with the loop. ~he port ~ontrollar is reguired to perform this re~uest. ~ ~ignslin~
~lgorithm is exe-uted to alect the test trunk circuit th~t a-_esa i, t~ be lroPped.
rhe LTS controller needs to free all 3~ equipment associ~ted with tha acces,.
20 DROPDDD -- lrop the DDD sallback connection and fcee the ~ss~_iated talk circuit. Relays are activated on the appr~priate talk cir-uit, ~nl the switching machi~e appearanca of the callback line is ~pened to inlicate "~ff~hook" . rhi a re~uest is performed by the LTS controller~

~193'737 3. ~ALK -- put the ~ssociated DDD callback ?ath into the mole th~t allows the Maintenance Gent~r alministr~tor to talk to the customer or craft at the end of the loop undec test. The LTS cont~oller -au~es relays to be oPerate~ on the talk circuit.
4. HOLD -- DUt the asso-iated _~llb~ck connection into the mode that allows testing to be carried out, but which keeps the callback Path connected. Talk circuit celays are operated by the LrS c~ntr~llec.
5. MONITOR -o put the associated c~llback connection in the mode that Pr~vide~ a high im~edance bridge connection, so that the Mai~tenance Centar administr~tor can listen ~n the tested lo~P. Talk circuit relays are ~perated by the LTS controllsr~
60 MON ~EST -- keep the high imPedance monitor mode on the callback connection while the next test is Performed, so that the Maintenance Center aAministr~tor can listen on the tested loop ~hile the test i~
being p~rformed. ralk circuit relays are ~pec~ted by the LTS -~ntroll2r.
~5 7. RIN~ -- atta^n ringin~ distributor cir_uit 2500 to the loop un~er test, and apply ringin~ voltage ac_ordin~ to the ON-~FF code contained in the re~ue;t me,sage.
Also, monitor for the ring-trip (customer ~ff-hook) in~ication, an~ conne~t 2 ~ain amPlifier to the callback Path~ if required.
Relays are operQted by the LrS controller on both the talk circuit and on the rin~ing listributor circ~it.
8. GAI~ allocate an ~mplifier circuit to the loo~ under test, and connect the ~mplifier to the associated _allback -onnection. Talk circuit relays are ~perated by the LTS ~ontcollar.
3. NOG~IN - remove the 3ain amplifier ~ssociated with the callba~k connection.
ra~k ~i~cuit rel~ys ~re ~oerated ~y the LTS
_ontroller.
10. DELAY -- wait for the sPecified time interval before executin~ the next test ce~est. The fancti~n ia pc~viled by the LTS controller, using the OS ti~eout facility~
11, KEEP_EQT_SETUP -- ter~in~te prosessing for the ~resent request mess~ge, but do not free the PMU now allocated for testing ths given 103~. This featlre ia provi1ad by the L~S
oontroller.
12. ~HRr_~ETECT -- ~onitor the looP for a short condition (less th~n 3~K ohms) between either conductor and ~round, or between the two loop con~uctors. This feature is provided by the ~ort -ontrol1er, and requires that a DC source be applied to the looQ, and th~t the loop -urrent be m~nitored for state ch~nges.
13. ~TA -- manipulate slesve leal current to activate the -entral office in~band signaling ciccuit, s~ th~t ~ test of the customer's key pad can be per~ormed by the poct controller. A source is applied to the sleevs lead.
14. rR~CING_TONE -- aP~ly a continuous tone from tracing tone source 2300 to the loop lndec test, aO t~at ~rRft personnel -an locate the pair under test in the outside 3; plant. ~he -ontinuous tracin~ tone source voltage of the LTS is aPPliel to the loop under test in either a metallic ~c ,. ~

3~3~7 lon3itudinal mode, as per the reguest ~arqmeter.
15. rhe following five requests leal with sleeve lead -ontrol circ~it 2500, ani are used for signalin~ the centr~l ~fice equipment to att~ch _ertqin e~uipment or to perf~rm some service. All sleeve le~d manipulation is done by the port controller by a~plying q DC source to the sleeYe lead circuit 2500.
a. HI_NEG_SLEEVE -- hi~h sleeve cucrent with negative battery b. LO NEG_~LEEVE -- low slaeve current with ne~ative battery c. OPEN_SLEEVE -- oPen cir-uit the slesve leal d. HI_POS_SLEEVE -- hi~h sleeve -urrent with positive battecy e. ~O_POS_~L~EVE -- low sleeve current ~ith p~sitive b~ttery 16. ~AZ_POT_STATUS -- check for the existence 3f a hazardous p~tential on the loop under test (port controller) by quarying thresholding cir-uit.
17. AUX_CONNECT -- connect two loops to a ,ingle PMU t~ allow louble-,idel resistive fault sectionalization tests to be ~erformed. rhe LTS -ontroll~r ~rfocms this o~eration by oPerating ralays.
18. CALL -- by m~nipulatin~ relays ~nd -ir_uitry on the associated talk circuit, ~lace a low impeian_a acro,s tha lin~
_ircuit of the loop under test, so that a M-aintsnance Centar a~ministrltor can simulate customer dialin~ action. This facility is provided by the LTS contcoller.

~L~g3~3'7 19. EXTEND_TO -- ch~nge the over~ll timeout on the loo~ access to the value specified in the present ~ess~ge tLTS controller)O
20. CON_TP_SLV -- connect tip to sleeve in ~rder to ~ia~nose test tcunka. ~he ~rt _ontroller provides this feature by operating relays in the port circuit.
21. DCON_TP_SLV -- disconnect tip and sleeve (similar to the above reguest).
rha following test re~uests are performed only by the Precision Measurement ~nit 2101, 2102 or 2103; the listing is exe~plary of the type of testing effected by a PMU.
1. AC3rY -- ap~ly AC sources and measure resultant current to produce values that yield a Thevenin e~uivalent _iccuit foc the loop at the applied frecuency.
2. ACDC~ short -ircuit the loop conductors to ground, and me~sure th_ resultant current flows.
2~ 3. BAL -- aPply a b~l~n-ed AC source to the loop, and me~sure the result~nt loop lon~itudinal balqnce.
4. DCT -- Produce only the DC portion ~f ths DC3TY test su~m~rize~ bel~w.
5. Dc3ry - aPply both DC and AC sources to the loop, and me~sure the resultant currents used to calculate ~n AC and DC
rhevenin equivalent circuit for the loo~.

6. DTA ~- draw ~ial tone from the -entcal office, ~n~ ~e~sure the characteristics of the dial tone si~nal sent ~ver the customec lo~p~

7. FRE~_DETECT -- measure the sign~l level ~t the fre~uenc~ spacified in the ce~ueat d~ta.

8. THEV -- execute ~ spe-ial DC
meaaurement ,e~uence for ~enac~ting ~urrent measurements in cases where ~ Thevenin .

3L~93'73~

aquivalent circuit is to be obt~ined for a -irclit known to have low resist~nce values.

9. ~CFEMF - me~sure open circuit forei~n voltage present on the loop under test.
10l PBX3rY -- execute ~ sDecial DC ~nd AC ~est al~ocith~ foc generating data used to leterm~ne the Thevenin e~ival~nt cir_uit for PBX equipment. ~he P~X lttendant is not ~lected by the appli-ati~n of te,tin~
voltages.-11. P~XDC~ -- s~me ~a PBX3TY, ~ut f~r a DC characterization onlyO
12. RCNT -- determine the number of rinqers presPnt on the loop under test by Daking a series of AC current measuremen~s when sources of various fre~uencies are applied to the loop.
13. RDA - alert the cust~mar t~ st~rt dialin~ a di~it zero on the ~i~l, anl measure the dial parameters.
14. ROH_RLS_TNK -- execute an ~lgorithm th~t ^auses release of a permanent si~nal circuit so that the receiver-off-hook test c~n be D erformed~
15. RO~_S~UR - measure the presance of ,purious si~nal ener~y at the f~e~uencie, use~ in the receiver-off hook measurement.
15. ROH_TEST -- ~pDly the re-eiv-r-~ff-h~ok test signal, and measure loop currents at har~onic fre~uen_ies.
17. ROH_VFB - aPPly a source volta3e anl ~easure the cesultant lo~p -urrent in oc~er to ~pproximate the length of a 160p with a ~IP-RING sh~ct.
18. SOAK - aPPly a ,e~uence of DC sources to the loop, and measure result nt curren~
fl~ws.

~93'7~7 19. rHER~ -- apPly a high level AC volta3es to the loop, and meaaure the result~nt current flows to detect ~ thermistor.
20. SSRFAULT -- execute the sin~le~si~ed resistive f ult aectionalization mea,ure~ent al~orithm.
21. CN_DTF -- totalizer ~etection for a -oin-first c~in telephon~ s~t.
220 CN_TOT_DTF -- totalizer homing func~ion ~or 1~ ~ coin-first coin teleph~ne a et.
23. CN_CF -- determine the resistan_e of the -oin circuit tot~lizer so th~t pcope~
-urrent can be a~lied to home it.
24. ~N_r~T_CF -- h~ma th~ coin circuit totalizer, and monitor for current flow.
2;. ~N_RDET -- maasuce the rasistance of the coin relay in or-~er to d~ter~ine the Proper source for the coin return function, 26. CN RCR -- apply sour-es to proper polarity in order to collect or return a _oin in coin telePhone set.
27. ~ RFV - measure the r~si,tance of the ground oath in a coin set.
2.2.1d L r,_c __tr_lle___ir_ui_ry Each _ontroller within LTS 160, n~mely, LrS
-ontroller 2C00, port controller 22~0 and a controller embed~ed within ea_h PMU 2101-2103 tto be discussed in a l~ter section), is imPlemented with basically the s~me circuit topol~y; it comprises ~ micropc~ce~sor device ~nd ~ncillary support ~evices. This topological arraagement is no~ presented with reference t~ LTS _~ntrollec 2000.
Because of its similarity to the other two controller types, th~ ~esc~iPtiOn aDplies to the l~tte~ two controllers with variations easily reco~nized by those skilled in the art.
LrS c~ntroller 2000 is composed of a microcom~uter-b~sed CPU, re~d only memory SROM), random ~g3'7~

~ccess me~ory (RAM~ and input/output f~-ilities ~I/~).
Also provi~ed i, an interrupt structure allo~iny as~nchronous evants to be recognize~ and a~ted upon~in an order-of priority manner as ~el~ q, ,uit~bl3 sy,tem timin~.
rhe CPU is impleme~ted with an 8 bit mi-ro~rocessor having a 16-bit address bus, thereby ~llowin~ acce~s t~ 64K bytas of memory. ~ha microprocsssor has a memory-maD~ed I/O structure that all~s for ~lloc~tin~ q poction of the memory ~ddress space for I/O
~e~ice selection. For LTS _ontroll3r 2000, 8~ o~ the upper address space is allocated to I/O (qs contr~sted to 6K ~or port controller 2200 and 4K or the PMU controller).
Of the ramaining memory associatad with Lrs _ontroller 2000, 16K is provided by RAM ani 40K by ROM. Of the latter memory, 20K is common to all software ~peration,, and 20K is bank swit-hel so th_t one ~f three different segments may be oPerational ~urin~ a ~iven processin~ se~uence. (For Doct controller 2~00, the memories imPlemented comPrise 18K of RAr~ anl 40K of RON, th~ l~tter having two 24K ,~itched segment,. F~r the PMU
controller, 15K of RPM is augmented with 48K of ~O~, 16K o~
which is switched from one of four bank~), Act~ally, - qddress decoding in the 54K byte addressing s~ace is ROM
programmable, thus allowing memory ~llo~ation ~nd I~O
functions to be placed in anY segments desired, so the ~bove allo-ations describe but one illustrative embodiment.
One I/O function ~e~uires ~ommuni-qtion via the GPIB prot~~ol, and this is typi_ally implemented with a ~tqndqrd GPIB qlapter devics. ~nother reguired l/O
function is ~o~uni^ation in a seri~l, bit-oriented mode re~uired by the high level data link Protoc~l. Agqin, ?n appropriate commer_ially-available devi-e interfacea to the memory-mapped ,pace. Finally, ~n in~erfa-e is provided or stanflard direct memorY access t~MA) devices to provide handshake conditioning for the high-~peed d ta -hannels if an increased throughput rate is required.

'73'7 rwO pro~rammable devi-es complete the basic implementation ~f LrS controller 2000; the,e include a orogrammable interrupt controller (PIC) an~ a progr~mmable interval timer (PIr).
S ~he PIC levice typically supports eight vectored interrupts with either a fixed or rotating priority~ Each input can be individually ~ske~ via softwlre _~ntrol. Two ~f the int3rruDts ace used in coniunction with JPIB and PIT
levices. rhe l~tter input provides ~ cryst~l ~ontrolled, timed-interval interru~t th~t allows real-time ^lo_k ~ppli_ations su_h as system time-out functions.
The PIT _ontain~ threa inl2~enlent 16 bit ~ounters. Each counter has operational modes to provid2 various c~Qnter~ti~er functions such as event c~unting, s~uare-wave generation and ~oftware controlled stroking.
~he clock in~ut to the clock divider circuit i, provided by a 4 NHz crYstal- ~he out~ut clocks ran~e from 15.525 kHz to 2 MHz and one may be selPctel t3 drive the CPU
microprocessor.
~0 2.2.2 Port_Controlle_ Port controller 2200 is also a mi^ro-omPuter-based system running under the ,ame ~pecati~g ,y~teD (Oa) lS DCN 140 and L~ controller 2~00. In port -ontroller 2200, the following tasks may be identified:
(a) PARALLF~ DATA ta,k controls the transmission and reception of messages ovar bus 20001, which typically implement~ tha GPIB protocol. It _ommunicates with the corresponling task in LTS contr~ller 2000 and i; ,i~ilar in structure and oper~tion, the main differen_e bein~ that the P~RALLEL DA~A task in LTS ~ntc~llec 20~0 ,erv2s as the bus master.
(b) ACCESS/TEST ta,k exec~te~ the a-~ess algorithm for NrT and NDF ~_cess. rhis in-ludes control of the following devices: ~1) port circuits 2801-2~16 and _orresponiing sleeve circuits 2817-2832 to connect to the appropriate no-te,t trun'~s 3401 9415 an~ t~ control the magnitude ~nd polarity of sleeve current; (2) trunk ~93 7.~'7 ~ialer 2650, of either the dial ~ulsing or multifre~uency type, depending on the central ~ffi_e swit_h ty2e:
(3) busy/speech detector 2500 to determine DC busy anl speech busy conditions; (4) tr~cing tone source 2900 for l~n~ tarm lppli_ation of 2air i~entific~tion t~nes for the loop; and (5) P C~NTROL se-tion 2702 of EAN 2700 to guide l~cesa and then connect the above-identifie~ device, t~ the accessed pairs when required. rhere are a maxi~um of aixteen active ~CCESS/TEST task~, ~ne f~r e~ch ~rt/sleeve circuit. However, the task-to-Dort qssignment is not fixed, but rather dynamically ~lloc~ted dependinq on the number of active accesses.
(c) ~DMINISTRATIO~ t~sk ~erf~rma all administr~tive functions in Port controller 2200, includin~
energizing the internal timer P~ri~lically ,o ~a to prsclude ~ system reset as well as ~cce~tin~ d~ta base lownl~ads ~t ays em initialization. Again~ the task structure is similar to the ADMINISrRATION task of LTS
controller 2000. ~he syste~ reaet is tcananitted DOt~
bus 20001 from LTS controller 2000 to all LrS 160 componenta ~nce a reset re~est is initiata~ UP the hierarchy.
(d) DUMP ~N task is ~ctivated after a ~icroproce-asor ,nalfunction ~nd is arranged to Provide f~r transmission of blocks of memorY to LTS controller 20no;
tha memory snaPshot focuses on the t~sk that was active when t~e malfun^tion occurred.
(e~ DIAJNOSTICS task pr~vi~e, aalf-tast c~pabilities for the har~ware controlled by port c~ntr~llec 2200 as well as intecfacing to aelf-test, foc LTS controller 2000 and P~U's 2101-2103.
Further discussi~n with reapect t~ p~ct controller 2200, Particularly t~sk Drocessin~, is deferced to Section 2~2.~ a~ that the de,criDtion r2latin~ t~
P~U's 2101-2103 ~ay bs integrated into tne operati~naL
iaa-ripti~n.
2.2.3 Pr_c si_n_M_a_uremeat_Unit_(PMU) ~L93'~37 FIG. 17 depicts, in block diagra~ form, the atr~cture ~f PMU 2101 (PIYU 2102 and PMU 2103 of FI~a 11 are essentially the same as PMU 2101 so it is taken as reoresentative). PMU 2101 is a micropr~cessor -ontrolled, ~eneral ourpose test instrument in th~t no ~art ~f P~U 2101 is dedicatel to performin~ any Particular test and this ~nit ,erves a~ the primary neans for me~surin~ the electrical Parameters of the subscriber loop under test.
rhe f~llowing interrelated subsystems comprise ~MU 2101: PMU controller 31~0; source ~enarator 3200;
source appli~ue 3300; detector 3400, measucement processor 35Q0; and digital ~i~nal processor 36000 ~ubsystems 3200 and 3300 ace connectad in s~sc~le nd this cascade arrangement serves to generate and -ouple the re~uisite sign~ls needed for testing to sub,criber loops (1aO or 181 of FIGo 2)~ Detector 3400, in -onjunction with ppli~ue 3300, serves to detect currents on the 1Oop under test and to convert these currents to corresponding voltagesO aubsystems 3500 ~nd 3600 comprise a series combination whi_h processes these voltages ~nd formats the processed signals for transmission, ultimately, to FE
computer 220 or 221 (FIG. 2). In the local PNU
envlr~nment, PMU controller 3100 receives test requests from LTS contr~lle- 2000 (FIG. 11) over p?c~llel-orien~ed bus 20001, sets up the test by intecfacing to the various subsystem-a via its busses 31001 and 31G02, ~nd tranamits the results of testin~ across bus 20001 u~on completion of testing.
~ourca generation subsystem 3200, depicted in block diagram form in FIG. 18, produces (i) the requisite AG and DC signals that are applied to l~op 180 or 181 via rIP leal 32002 ~nd RING leal 32003, and (ii) demodulating signals, on leals 32004 through 32007, nec~ssary to drive measurement processor 3500. Generator 3200 ia ~da~ted to ~rovide composite AC-DC signals simultaneously to rIP
lead 32002 and RING lead 32003. To ins~re cea~luti~n of fault conlitions within predetermined t~ler~nces, 3'73~
~ 64 ~enerator 3200 is ~rranged to produ_e:
(a) ~ single AC aign~l h~vin~ ~ frequency from 1 H7 to 32~0 H~ in 1 Xz steps at voltage levels fro~ 0.3v to 12.75v rms in O.O5v s~eps and from 12.8v to 95.6v rms in ~.4v steps. The a~_uracy ls +0.1v cms or 3~, ~hichevet is greater;
(b) a DC signal at a level fcom ~ t~ + 51v in 0.2v ste~s and from ~ 51.15v to + 1~5.3v in 0.55v ste~s.
~he accuracy is +0.1v or 2~, whichever is greater;
(c) a swept fre~uency si~nal where the startin~
fceauency, stopping fre~uency and frequency inc~ement may ba spacified within broad limits;
(d) a p~lsed ton2 wh~se cate an~ duty cy^le may be ~pecified over a broad range, (e) a signal comPrising the sum of two A-aisnals having the same rel2tiv2 am~litude; and (f) a signal formed by sequencin~ through

10 tone p~irs each of whose fre~uencies may be speci ied over the c~n~e from 1 Hz to 3200 ~z and whose iurations and silent int~rvals may be spe_ified.
3esides producing the aforementioned signals (a~ - (f), ~enerator 3200 m~y ~lso be confi~ur21 so that diferent DC levels may be applied to TIP and RING
le~ds 32002 and 32003, respsctively, at the same time or that the apolied AC si~nals hava tha saDe ~nPlitud2 but are phase-shift2d 180 degrees relative to each ~ther.
~raover, ~mbinations of ~n AC signal and a DC signal, as defined in ite~s (a) and (b) above, ~ay be provided as long ~s the peak value of the composite aignal is le~s than 135.3 VOlta.
Sour_e generator 3200 typically comprises a set ~f microco~puters (not shown in FIG. 17). Each of thesa o~omputers ~enerates di~ital samples via a table lookup techni~ue. For AC signals, these digital s~mples are -onverted to analog form by means of digital-to analog (D/A) converters embedded within ~enerator 3200. ~omposite aignals are foc~ed by combining the OUtpUta of the D~A

_onverters with a DC level.
~ he MLT performs mainly admittance mea~u~ements.
In order to test subscriber loop 180 or 181 of FIG. 2, the si~nal volta~es pcesent on ~utp~t l~qls 32002 ~nd 32003 emanatin~ from ~enerator 32~0 are apolied, via source ~ppli~uo 3300, to TIP and RING leads 33001 and 33002, respectively. ~he resultant longitudin~l-m~de -urcent flowing in leads 33001 and 33002 are each indepèndentlY
letected in applique 3300 by me~ns ~f a magneti~ sensin~
circuits (not shown). The outputs of the m~gnetic circuits ~re si~nals proportional to the detected currents and these ~ignals ap~ear ~n multiple leads 330~3 qnd 33004 em~nating from ~ppli~ue 3300. Detector 3400 receives and then sonverts these signals to v~ltages prop~rti~nal to the sensed currents. ~utput leqds 34001 and ~4003 from detector 3400 carry voltageâ Dr~30rtion l t~ TIP cu~rent in the usual measurement mode, whereas output leads 3400? ~nd 3~3~4 have voltqges proportional to RI~G current. rhere is also a measurement mode wherein aPplique 3300 anl detector 3400 can be config~red to produce voltqges proportional to a longitudinal -urrent qnd the metallic current associated ~ith the lo~3 un~er test.
rne signal processing section of PMU 2101 comprises: meqsurement 3ro-ess~r 3500, with circuitry including multiPliers, analog multiplexers, anqloq-to-ligital (A/D) c~nverters and sample-and hold (S/H) circuits; and digitql signal processor 3600. In-phase (TIP(I) and RIN~(I)) and ~u~drature (TIP(~) and RING(Q)) waveforms ~t precisely the ~reguency aPPliel to the looP
~nder test represent one arrangem2nt of signals present on leads 32007, 32005, 32006 and 32004, res~e-tiv~ly. These w~vef~rms m~y be produced in generator 3230 as the counterParts to the signals aPPlied to the loop under test ~nd these four waveforms are used to synchronously demodulate the volta3es produced by detector 3430 on le~ds 34001 and 34002. Anqlos multipliers embedded within pr~cessor 3500 perform the demodulation. F~r inst~nce, the 373~
~ 66 -output of one multiplier is a signal for~ed by multi~lying the first detector voltage, on le~d 34001, by the in-ph~se component of the signal on the rIP (TIP(I)) apD~aring on lead 3~007. If the voltage on lead 340~ the ra,ult of current flow on the TIP of the loop under test, then tha ,ignal fr~m thi~ m~lti~lie~ is proDortionql to the real part of the admittance~to-grounl of the TIP conductor.
Anti-ipated phase shifts both within ~ircuitrY f P;~U 2101 or due to e~ternal circuitry cqn be ac-ounted for and accommodated simply by phase shi ting the ~em~d~lat~r sign~ls aPpearing on leads 32004 through 32007 relative to the sources applied to the loop via lea~s 33001 and 33002.
In addition, harmonics of the frequencies appliad to the loop under test can be generatel within source 3200 and used to detsct nonlinearities in the loop aimittance by se~rching for D~ components in the outputs of the multipliers. The use of two si~nal conditioning channels (34001 an~ 34002) and four demolulating si~nals (on leads 32004 thr~u~h 32007) ~llo~s P~U 2101 to mqke multiple measucements sinultaneously. In the embodiment, the results of all ~ea,srements are DC values~ either initiallY
or ~fter the demodulation proce,s.
Meas~1ceme~t processor 3500 is Us2d to select from ~mong the vari~us outputs appe~ring simultaneously from the ,nultiplie~ outDuts ~nd dete-tor leada 34001 thr~ugh 34004, rhe signals so selected, typically in p~irs, are fe~ to S/H
qnd A/D circuit, contained within p~oce,s~r 3503. ~he digital samples, em~nating from processor 3500 on one conductor of multi-~nductor 350~1, ,arve q, ingut t~
ligital signal processor (D~P) 3500. DSP 3500 imPlements several digital filterin~ ~rograms, one of whi-h in~ludes a dYnamic settling algorithm that is utili2ed to ~eci~e ~hen ~ finql Y~lue hqs been obtained from a measurementO Test cesults are Passed from DSP 3600 to PMU controller 3100 over bus 31002.
As indicated by the foregoing discus,ion, P~U 2101 Pffect,, within ~radetermined volt~e and ~937;~'î
~ 67 -fre~uency limit~, ~easurements to ~h~ra_terize ~ three terminal network, including those of a distributed ~acameter natura exemplifie~ by a two-wire, shi311ed transmission line (that is, the customer loop).
2.2~3a Di~it_l_S ~nal GeneEat-E-(D~) ~ he procedure used to generate cosinusoidal waveforms with ~enerat~c 3200 ~f FIG. 17 inv~lves a-cesaing signal values that have been stored ~ithin its read-only me~ory. ~he value, that are selected a-cor~ing to the techni~ue to be described ~ra tcansformad into a -osinusoid~l wavef~rm via a digital-to-anal~g c~nvecter and low-p~ss filter means.
~ he values stored within the memory of ge~erator 3200 are, basically, magnitude sanples OI COS 9 foc the ~irst and third qua1rants. ~lthough symmetry of a _osine wave would permit it, reproducti~n f~om ,amples ~f one quadrant only, higher freque~cy si~nals are effec~ed by providinq tw~ aet, of samPles t~ rel~ce tr~nsf~mation time in matching the samples to a form accePtable to the di3it 1 t~-analog ~~nverter.
The values for ea-h quadr~nt are 4 ccessed with an eight~bit address, aO 256 memory lo-ati~n, per ~uadrant are stored. rhe mamory for the first ~uadrant stores +cos 9 over the range C to 90 degrees with 9 having a s~acing o~
0.3516 degrees (90 degrees/256), whersas tha other memorv ,tores -co, 9 with the same s~acing.
Each o~ the values stored in the memory is contained ~ithin an eight-bit 4~rd. Ea~h v41ue ia ~n integer representation of the decimal numbar obtainad by avaluatin3 the _osine ~ith the fore30in3 sp~cin~. rhus, if ctn) raPresents the nth value, the inte3er storad at ths nth addrea, is ctn) = 256 I ~ cos(-24~
where I~.] desi3nates an integer truncation operation to 9 bits an~ n is su-h that 0 < n < 255. ~he multiplicative factor 255 in e~uation (1) basi~ally left-shifts th3 ~ecimal values resulting from truncation. (If the memorY

~193~3'7 - 6~ ~
word-size ia ~ in general, ~, anl the number of addressable locations in memocy is 2 , then e~u~tion (1) h~ a the focm c(n) = 2 I ~ cos~L~2 ~ , for S 0 < n ~ 2 -1, which radu_es to 3~uation (1) for K = L = 8)o ~he -_os 3 tàble, that is, the v lues in memory ~ssociated with third ~uadrant samples, is the 2's ~omplement version of the ~cos 9 table. The comelementary relationshi~ of these two ~blea ,av2s axe_uti~n ti~e that would be needed to generate the com~lemsntary values if on~y first ~u~drant values were storea~ Since the particular embodiment of the present invention utilizes a li~ital-to-~nalog converter req!liring an offset binary code to produce a four guadrant waveform, any table value requires only the insertion of the proper ~uadr~nt sign value to complete the offset binary code.
Besiles the +cos 3 table, gener~tor 3200 utllizes an accumulator to obtain a sample index and ~uad~ant pointer. With reference to FIG. 19, the ac-umulator comprises cegistera 3210, 3211 Ind 3212 whi-h, tyPi~ally, represent three contiguous bytes (8-bit words) in memory.
rhe boundaries for these thcee bytes are chosen such that bits 0 and 1 of the high byte (register 3210) -ontain ~uqdrant inform~tion in the form of a ~adrant p~inter.
For instance, if these two positions hal the binary values '0' and '1', respectively, then thicd ~uadr~nt values are re~uired. Th~ ~u~lrant inf~rmation is passed to sample aelector 3213 on lsad 3251. The entire mid~le byte, ~omprising register 3211, provides the ~ddress of the s~mple to be selected by selector 3213~ This ~ddress, -alled the sample index, is pasaed to sele-tor 3213 via parallel-~riented bus 3252. Bits 4 through 7 of the low b~te ~register 3212) contain the four least si~nificant accumulator bita~ .

:~g3737 - 69 ~
Freguency generation is a_com~liahed by the binary additi~n of a 12-bit fre~uen_y ward, arrivin~ on bu~ 3254 ~ to tha 12 least signifi~ant bits ~f what is, in efect, a 14-bit accumulator. ~he frequency w~rd on 5 bua 3254 ia indicative of the fce3uency of the _~aine t~ be ~ener~ted, as expl~ined shortly. The a~dition occurs at a fixed r~te, designated fs (Hz), which is typically ~t least twi~e tha highaat frequency cosinus~id to be pc~vided by ~ener~tor 3200.
In general, as the fr~uency worl is ~ddel to the ~c~umulator at the rate f5, the bits of register 3212 eventually ~vecfl~ int~ re~ist~r 3211~ In tucn, register 3211 eventually overflows into register 3210.
After each addi~ion, the tw~ bits of re~ister 3210 ~re checked for Phase information and all bits of ragister 3211 ~re p~ssel to sala_tor 3213. A cosine ~a~nitude value is appropriately extr~cted from the ~cos 3 tables storeQ
~ithin seLe~tor 3213. A polarity sign is s1p2lied to the value, and the now comPleted encoded value is p~ssed to digital-t~-an~l~g converte~ 3214 vii bua 3253.
In view of the foregoing liscussion, if a _osinusoidal fre~uency ~f 1 Hz th~ving 1 fragua~cy wocd representation of 00000000 0001 in binarY) is t~ be ~enerated, then it would re~uira sixteen ad~iti~ns to the accumulator ~initializel to 00 00000000 0000) beore cegister 3212 ~verflows into rs~ister 3211. Thia maans that for one comPlete cycle, wherein the t~bles will be indexed ex~ctly 1024 times, one table valu2 is ~ccaased sixteen consecutive times, another value sixteen consecutive times, and so forth. Thus the aame encaded cosine value is loaded into converter 3214 sixtaen times bafor~ a new encod2d value becomes availabl2. However, if a frequencY ~3rd of 00000001 0000, representing 16 Hz, is added to the accumulator, then 1024 sample indices are ~till produced, but a ned ~nd diffecent en_oded cosine value is 13aded into converter 3214 ~ft2r every addition.
LO reiterate, if the fre3uency cePresented by the fce~uency ~L~L93 73~
_ 70 _ word is sD~ < 16 Hz), the co,ine maqnitule v~lue, do not change ra~idly, that is, they become "dwellad" on for period of time, whereas for a l~nger freguency w~rd (> 15 Hz), the ~osine samples change raPidl~, ~he result of this generation technique is a _osinusoil~l ~ave synthesi~ed by steppins throu~h a look~uP
table, sm~ll steps for low frequencies ~nd large steps for high frequencies. ~he fre~uency spectrum for ~ wave aynthesized in this manner contains the de3ired fundamental freyuency Plus its harmonics. Also present is the sampling fre~uency f5 and its harmonics. Mora~ver, the lesired freguency and its harmonics are centered about fs and its harmonics. To reduce distortion dua to ali~sin~, ~s is at least twice as ~reat as the highest frequency to be produced. In addition, a low p~ss filter~ desi~nated as filter 3215 in FIG. 19, rem~ves frequency ~omponents above fS/2, thereby pcoviding a smoothing operati~n.
Besides the frequency comPonents disc~s,ed ab~ve, there are undesired freguen_ies due to lwelling on taDle values during the generati~n of low fre~uen-ie, and the finite pracision of converter 3~14. These fre~uencies are ~ubharmoni-s anl filter 3215 c~nnot rem~ve them since they fall within the Passband~ Fortuitously, howev2r, the ~mplitudes of the su~harmonic components ace s~all lue to ~5 minor differences in adjacent t_ble values and for ~onverter precision on the order o aight bits per sample:
therefore, the harmonics ara tolerable without further Pr~cesain~ .
2.2.3b N~qne_~_C_rr_~t Sens_r As briefly discussed ~bove ~ith refecance t~
FIG. 17, source appli~ue 3300 and datector 3400 combine to datect appropr1~te conduct~c current,, tYpi_~llY
longitudin~l mode -urrents in both the rIP and RING of the l~op undec test, and then t~ convert tha datected conductor currents to voltages suitable for processin~.
A mora detailed block dia~r~m of ~urce aPPligue 3300 is shown in FIG. 20. Signals tr~nsmitted ;

~9~'7~î

fc~m sour~e genarator 3200, via leads 32002 ~nd 32003, serve as inputs to rIp sour-e driver 3301 and RI~G ,ource driver 3302, respectivel~. Drivers 3301 and 3302 Provide hi~h imped~nce buffering t~ the inQut si3n~ls ~nd ,uitably level shifted ~utput voltage or curcent signals to ener~ize output TI~ lead 33001 and RING lead 33002, respectivelyD
~ource impedance values presented to the rIP anl RING are effected b~ impedance netwo~k 3309 -~uPling driYer~ 3301 ~nd 3302 to lea1s 33001 and 33002, respecti~ely~
Drivers 3301 and 3302 and netw~k 3309 pr~vide ~ hi~h degree of tesking flexibility. Voltages fr~m 0 to + 135.3V
peak and currents up to 125 ma can be delivered through a variety of source impedances. rhe choi^e ~f in~edances ranges from a short circuit up to 100 K ohms in series with both rIP and RING ~c each separ~tely. M~re~ver, TIP an~
RING can be shorted or capacitively coupled. A~pli~ue ^ontr~ller 3311 si~nals network 3309, via lsad 33~11, as to the desired coupling imPedances. Controll2r 3311 oPerates in respons2 to si3nals transmitted over busses 31001 and 35001.
Magnetic core paic 33~5,3305 ~ss~iated with ~IP
lead 33001 and core Pair 3307,3308 ~ccompanying RING
le~d 33002 dete~t flux chan~es induced by -urrent carrYing conductors which are wound through the -ore apertures. For instance, with the re1ay contacts ~f relay ~ in the make and break positions shown in FIG. 20, the rIP lead current ~n conductor 33~01 forms a two-turn winding on each core 3305 and 3306; similarlY, the RING lead current on conductor 33002 penetrates the ~pertures of core pair 3307,3308 twice with the same ~rientation. However, if relay A (whi-h is e~bedded within appli~ue _ontroller 3311) is energi~ed, then core Pair 3305,3306 encompasses the TIP lead only once and the _urrent in the RING lead is ~l~o r~uted through core Pair 3305,3306, but in a sensa ~pp~sin~ TIP le~i current. In efe_t, -~re pair 3305,3306 detects a differential bet~een the in~ividual _urrents flowing in the ~IP and RIN~ leads 33001 ~93~

and 33002, respectively. Thus, the two operating modes of relay A determine the desired routing of current carrying paths through core apertures. More complex relay arrangments enable numerous measurement modes as well as fault location procedures for a variety of loop fault conditions. Loop fault detection and location methodology which utilizes the foregoing current routing arrangement is the subject matter of UOS~ Patent No~ 4,424,479 which issued on January 3, 1984 to J~M. Brown. A synopsis of this loop fault locating methodology will be presented in Section 3O2 ld wherein the MLT system tests are defined.
Core pairs 3305,3306 and 3307,3308 are typically matched ferrite cores; ma~ching is required to minimize offset drift as ambient oonditions, particularly temper-ature, vary. With the core pairs and accompanying circuitry of the illustrative embodiment, currents from 1 ua to 500 ma in the DC to 3200 Hz frequency band may be measured with an accuracy of + 1 ua or ~ 1% for the anticipated ambient conditions.
A brief description of the operation of one core pair arrangement is presented with reference to FIG. 21~
Each core 3307 or 3308 has basically three windings. One winding, designated the line winding, comprises conductor 330013 in series with conductor 330014; these conductors are considered to form one winding because each provides aseries aiding field excitation. The conductor having ends 330041 and 330043 forms a sense winding, whereas the conductor having ends 330042 and 330044 comprises a control winding on each core 3307 and 3308. With the currents IL, IC and IS flowing in the line, control and sense windingsr respectively, and having the flow direction shown in FIG. 21, the line winding and control winding on core 3307 provide series-aiding magne~izing fields whereas the fields are series-opposing on core 3308, and each sense winding provides series-:~93'737 opposing fields to the line win~ing fields.
Operational amPlifier 34021 and -~pa~itor 34024 focm an in~egrato~ ~hich acts t~ feed back _urrent IS
through th2 sense winding on each core to c~ncel magnetic flux caused by the current IL in tha line win~in~. In steady-st~te ~p2ration, th~t is, after line current tr~nsients have di,sipated, the volt~ge on ~utput lead 34012 is proportional to the current IL on lead 330013 (oc 330014). In o~der to deternine if IS is of suficient ,trength t~ cqn-el IL, pulse generator 34022 periodically drives cores 3307 and 3308 into s~turation through the sep~r~te -ontrol winding of each COC9~ Ducinq ~he interval that cores 3307 and 3308 are driven into satur~tion with _urrent Ic, switch 34028 remains open~ ~hen the saturation Pulse is camove~, s~itch 34028 is conne~ted to the invertin~ (-) input of amplifier 34321, throu~h cesistor 34027, in order to sen,e the presence of an ercor voltage generated by collaPsing flux, that is, flyb~ck from ,aturation. If the net flux ca~sed by fiells indu--~ by IS
~nd IL current is zero, the volta~e generatod ~n each sense winding i, eau~l and oPpOsite and, consequently, tha error voltage is zero. However, if the net flux is not zero, the nonzeco ercor v~lt~ge is integr~ted anl st~red by c2PaCitOr 34024. During the next pulse cycle, the storad volta~e furnishQs ~urrent I_, through resi,tor 34023, t~
the sense ~indings and, accordinely, forces the net flux to zsro .
If cores 3307 and 3308 ~re not perfectly matched, primarily bec~e ~heir ch~ractaristics do not tr~ck durin~
changing ~mbient conditions, a nonzero error voltage may be 3enerated even if the line ~inding _urrent is zero. To ~artially correct for core offset, a compensating offset _urrent is fed into integrator ~mplifier by offset voltage corrector 34025 in series with resistor 34026. After offset correction, the oUtPUt volta~e on le~d 34~12 ,ubstanti~lly tracks the line current. In the illustrative embodiment, aut~matic offset correction achieves a two , ~3'73'~

orders of magnitude imProVe~ent in dete_tion performance as oompared t~ the circuitry witholt offset co~pensation;
~utomztic corce_tion occurs periodi_ally~ although for the most sensitive measurementa~ a _orrection is m~le immediately ~rior to a measurement. Offset _orre_tor 34025, which is typic~lly a di~it~l-to-analog converter, recaives a correction voltage from P~U
^ontroller 3100 on bus 35052. rhe voltage suPPlied by PNU
controller 3100 results from a test measurement, with ~sro loop _urrant, performed on the periodic basisO
FIG. 21 depicts the essential cir-uitrY of ring I-to-V converter 3402 of FIG. 22. As shown in FIG. 22, ring I-to-V convecter 3402 has corresponling _ounterpart in tip I-to-V converter 3401 which performs basically the same oper~tion ~n c3re pair 3305,3305 of FI~. 20. rhe output voltages proportional to TIP qnd RING leqd currents appear on leads 34011 and 34021, respectively, ~f FIG. 22.
In that eqch voltage signal is processed in basically the s~me manner with the remainder ~f the circuitry embedded in detector 3400, only Drocessing of the output voltage signal appearing on leqd 34011 of tip -onvarter 3401 is described in the follo~ing~
~ he voltage on lead 34011 is band-linited t~
3200 Hz bY filter 3403O For some measurements, particularly in a high 50 Hz noise anviron~ant, filter 3403 ~lso can provide 60 .~z band elimination filteringO
Filter 34~3 opsrat2s under -ontrol ~f lete~tor controller 3405, via lead 34053; in turn, date-tor ~ontroller 3405 receives instru_tions fcom P~U
controller 3100 on bus 31001 and DS? 3600 on bus 3~001.
~he filtered voltage signal appaar, on leal ~4031 and serves as an inPut to gain units 3408 an~ 3410. Gain ~nit 3408 2rovide~ either a gain of four or no gain as well as filterina with a 10 Hz high-pass filter; tha signal qt the output of g~in unit 340~, on lead 34Q01, ba~ically comprises only AC -omponents~ ~n the other hand, the output of ~ain ~nit 3410, on le~d 3l003, r2?res2nta a .

~g37;~7 -omposite AC-DC si~nal amplified by eithec ~ fa-tor of four or directly coupled without ~ain. rO detscmine which gain factor to aPply, the output~ ~f qain units 340~ and 3410 serve ~s inputs to saturation d~tector 3405. Initi~lly, both gain units 3408 and 3410 are set to the maximum gain ~f four. If the si~nal at ~ne ~r b~th ~utp~t~ is ~bove a preselected threshold, slturati~n detector 3406 interrupts PMU controller 3100. Interrupt as a result of ~C ~verl~ad appears on lea~ 34061, whereas _omPOsite signal overload is tr~nsmitt2d over lead 34062- Appropciate gain adju,t ,i~nals are ceturned to ~ain units 3408 and 3410 fr~m PMU
_ontr~llec 3100 via detector controller 3405 and, particularly, lead~ 34058 and 3~057. If s~tur~tion is still dete-ted, then an inPut attenuator is switched into 15 the current ~ath a,~ociated Nit~l TIP le~d 33001. ~he ~ttenuator~ depicted by element 3303 in ~IG~ 20, provides a ~:1 current ~e~uction. The signals thus appearing ~n AC-only lead 34001 and broadband lead 34003 at the output of letector 3400 repce~ent suitably scaled analog ,ignals 20 ~roPortional to the currsnts fl~wing on the loop conductor acrangement un~er test~
Now with reference to FIG. 23, ad~iti~nal pcocessin3 is effe~ted by the mea~ucement proce3s3c 3500 to prepare the an~log signals for li3ital filtering in 25 Processor 3600 (FIG. 17).
~he si~nal on AC-only lead 34001 is Presented to 7-1 MUX, that i~, the upper half of multiplexer 3501, on five parallel paths. The first path directly c~uples le~d 34001 to multiplexer 3501 ;o that br3adband AC signals may be mea,ured. To obtain the sign~l on the second path, in phase ,ynchr~no~s detsction is effected by ~llti~lying the voltage si~nal on lead 34001 with the rI~ (I) signal on lead 32007 in f~ur-~uadrant multiplac 3701~ Synchr~noua ~etection of the AC-only signal frequency shifts the inf~rmati~n be ing components to D~ for efficient filtering. Aliasing is mitigated with 10 Hz antialiasing filter 3513 interpo~ed between ~ulti2lier 3701 and ~ ~373'7 7~
multi~lex2r 3531. ~he fou~th plth ,ign~l ia obtained i~ a manner substantiall~ e~uivalent to the second Path processin~ techni~ue, the only diffe~ence bein~ th t a ~uadr~ture sign~l (rI?(~)) serves as an input to multiplier 3702, via lead 32006. rhe DC components emanatins from the aecond a~d f~urth pr~cea,ing paths represent typic~lly the real an~ im~gin~ry parts of the ~mittance with respect to ~round of the 1~P c~nductor arrangement under test, typically the TIP-to-ground path.
Oftentimes it is neceasa~y t~ mea;~re a c1rrent signal pro~uced by ~ voltage arising outside the ~L~ system for which the exact fre~uency i, n~t kn~wn; in this ~ase, synchronous demodulation is effected with an average fre~uency. F~r instance, l_al tone Providad to a tele~hone set is known to be in the 300 t~ 1000 Hz band. Syn-hronous in-ph~se ~n~ ~uadrature detection with a 65~ Hz frequency, followed hy filtering with 350 H~ l~w-pass filters ~511 and 3513, respectively, results in aisn~ls indi_ative of the ~c2sen_e ~f di~L t~na. The gu~lraturely-relatel si~nals are delivered to multiPlexer 3501 via multiplier filter pairs 3701t3511 and 3702,3513, respectively, on paths three ~na fiv~.
Finally, path six diractly ~resents the ~roadband, composite AC-DC sign~l to multipLexer 3501 and the signal on ~th seven results from low Pass filtering the signal on laad 34003 ~ith 10 H7 filter 3514D rhis latter path ia ~sed ~rimarily t~ measure th~ DG in the _omposi~e AC-DC signal.
rhe seven TIP Paths just descri~e~ are duPlicated by similar procesainq ~n the RING l~d aide an~ are received in the lower-half of multi~lexer 35010 The aisnals on all ~ourteen paths a pr~sent aimultane~uslYJ
Analog multiplexer 3501 is used to conn~ct one ~f the seven ~IP p~ths ~nd a corresponding one of the RING paths to sample-and-hold tS/H) devi_ea 3504 ~nd 3505, rsspectively.
Since pro3rammable ~ain amplifier (PGA) 3502 ia capable of proceasing only one input at a time, multiplexer 3505 ,-~9373~7 perfocms time division multiplexing on the outputs of S/H
levices 35~4 and 3505 and channals the desiced -aign~l t~
~ai~ amplifier 3502 during ~ppropriate time intervals.
Lead 35011 couples the uPPec~half 7-1 MUX ~f multiplexec 3501 t~ S/H 3504, ~nd le~d 35041 couples ,/H 3504 to 2-1 ~UX 3506. ~imilar functions are perfornled by le~ds 35012 ~n~ 35051, respe-tively. Finally, multiplexer 3506 and gain amPlifier 3502 are coupled with le~d 35061.
The output of gain amplifier 3502 serves as an input to twelve-bit A/D unit 3503; coupling ia via lead 35021. 5ain amplifier 3502 provides ~2in fr~m 1 to 256 in steps of 2. To detecmin3 the cocrect gain settinq for each sample presented to A/D unit 3503, t~r~
measucements are made per s~mpla. For the first measurement, PGP 3502 is set at unity gain~ The nu~ber of leading zacos in the 12-bit digital output ~n lead 35031 are counted~ For each laading zero, the galn is increlsed by a factor of two up to a maximum g~in of 255 ~c eight leading 2eros. The signal is a~ain measured nd converted to a 12-bit digital signal. This t~o-step ne~surement procedure ensures that the full conversion range of converter 35C3 is utilized for ~axi~um measurement accuracy. The 12-bit measured signal is combined with the setting on PGA 3502 to Produce ~ signal re~uiring a maximum ~f 20 bits fo~ -omplete repcea-enta~ion, Di~it~l si3nal processor 3600 is arranged to oeerate on these 20 bit signals, as will be discussed shortly~
Because of the parall2l processin~ arrangament of multipliers 3701 through 3704 and time ~ivision ~ultiplexin~ avlilable with multiplexer 3501, a number of analog signals ~e~lting fr~m a typical l~o? me~surament can be processed essentially si~ult~neouslyO For instance, ~ne measucement in the stanlarl set of cequests is the DC
three terminal admittance (DC3TY)~ '~ith this measurement, both PC and DC ~oucces are ~pplied between each lo~p conductor and ground, and the rasultant currents are used .

~1~3~3~

to cal~ulate an ~ and DC ~hevenin equivalent _ircuit of the loop. For instance, it is aupposed that the AC v~ltage is applied at 24 Hz. At a samplin~ rate of 100 Hz, the ceal and imagin~ry components of th- 24 ~z ,i~n~l ~ce Drocessed on p~ths two and four and the DC _urrent on path seven for both the rIP and RI~G conductors, resulting in a total of six me~surements from basis~lly one source signal.
Measurement controllec 3507 Pcovi~ea the re~uired timin~ inform~tion to synchronize operation of ~ultiplexec 3501, S/H devi_es 3404 an~ 3405 anl multiplexer 3505 to insure that the selacted an~lo~ signals ~ce avail~ble f~r A/D convecsion in element 3503, In addition, controller 3507 generates a prograssi~n of timiny aignals th~t activate, for example: the ficst nea,urement with ~/D converter 350~; the circuitry to count leading zeros in data from the first me~suranent; t~e ~in selection in PGA 3502 as determined by these zeros; the ,econd A/D ~easurement; anl the tranamissi~n of the 12 bits representing a sample to measurement interf ce 3508.
Contr~ller 3507 is dependent, initiallY, on information transmitted over bus 31001 from PMU controller 31001. ~nce ?ctivated~ however, controller 3507 produce, ti~in~
infor~ati~n b~sically independent of PMU controller 3100, ~lthough intercupts and reset r_quests may override and disable state timing.
Meaaucement interface 3508 serve, a tw~f~ld purpose, namely, (i) to tempor~rily stora the results of the first and then the second ~/D measurements and tii) to f~rmat the 12~bit ~ata obt?ined from the second measurement for trans!nissi~n to DSP 36000 DSP 3600 manipul~tes 20~bit, two's complement data with the Dresumption that the lea,t significant bit arrives first on its serial-oriented in~ut port. In the present situati~n, thi, input P~Ct is connected to one conductor ~rom channel 35001 a,nanatin~
fr~m neasocement interface 3508. F~rmattin~ is re~uired since data is transmitted serially between intarfa_e 3508 nl A~D converter 3503 on one c~nductor of Lea~ 35331 with 373~

the most aisnificant bit ar-iving first. In f~rmatting the data generated by the second measurement, a_count is taken oE the gain of PGA 3502, the po1arity of the s~plel signal ~nd whethar an extr~ gain, called "psuedo-gain", is to be implemented. The purpose of this extra gain is to reduce inherent error in pcocessing f~ low level ,ign~ls ~ue to a digital processing Phenomenon c~lled a "limit cycle" caused by finite ~ord len~th effects.
FI~. 24 depicts how FIGS. 18, 20, 22 ~nd 23 m~v be grouPed to form a comoosite ~f FIG. 17.
2.2,3c Sian_l_PrQ~_ss~ag rhe final stage in the pr~-essin~ of the dete~ted rIP and RING signals is effected by DSP 3600 of FIG. 17 DSP 3500 is cantrolled by PM~ c~ntroller 31~0 via bus 31002. PMU controller 3100 downloa~s the required processin3 algorithm into D~P 3500 via memory bl, 31002 and receives results back over this same bus. rhis downloading felture allows DSP 3500 to perform a wide vqriety of filter funGtions eYen thr~ugh DSP 3600 has limited memory size.
Nine diffecent filterin3 functions ~re presently implemented in PMU 2101; these include:
~1) A DC to-5 Hz low-pass filter function with 20 Hz ~ttenuations of 40, ~0 and 120 dB. The amount of attenuati~n i, selected on the basis of interference encountered in ~ particular measurement.
rhe attenuation is selected in real time by a dynamic settlin~ algorithm which releases the measured datq as aOOII lS it h~s settled within prescribed limits, typically five ~on,ecutive measurements ~ithin ~ne percent ~f e~ch other.
(2) A DC-to-5 Hz low-pass filter without settling with 120 dB ~ttenuation at 20 Hz~
~he value of the outPUt is p~vi~ed upon demand bY PMU controller 3100 as often as lesired.

1~3737 (3) A DC~to-5 Hz low-pass filter in which ~n in-phase/~uadcatuce p~ic is ~~nvected to magnitude s~uared value by a S~uare and add operati~n. ~esults ~re provided as iemanded by PMU -ontroller 3100.
(4) A DC-to-5 ~z low-pass filter usal for detection of asYnchronous tones such as dial tone and in band sign~lin~. This filter program provides the current filter output ~s often as it i~ re~uested by PMU
controller 3100, (5) ~ 5 Hz low-P~ss filter ~ith Peak lstection. rhe peak value of the signal is pr~vided onca on dem~nd by PMU
_ontroller 3100.
(fi) A broadband filter with mean-sguared ~utput using either 10 Hz to 3200 Hz flat weighting or C-messa~e weightin~. Filter output is provided by DSP 3500 on demand~
(7) ~ Drogram which _ounts the number of samples for which the input signal is ~bov2 the given threshold and the number of ,amples for which it i5 below the same threshold. Countin~ begins ~n the first high~to low transition of the inPUt or on the first lo~-t~-hi~h tr~nsition depending on a parameter transmitted by PMU
^ontroller 3100. A count i, returned on each transition so that rotary ~ial ~ulses may be analyzed.
(8~ A program which detects the voice-frequency ran~e tone blrsts from coin ohon2 t~talizers as well as the DC current flowin~ in the loop associated with the coin phone. An indication is sent to PMU controller 3100 ~fter each t~ns burst is received. ~he value of the DC surrent is returned after ~3737 _ ~1 the last bucat is re~eived. Test timing is ~ls~ include~ in this pr~r~m to identify -ontinuous tones, no tones ~nd test time-~ut.
(9) A QC~gram which pecf~rms self-dia~nostic testing ~n D~P 3600, including its internal memoryO
FIG. 18 indicates that DSP 3600 _~m~rises basically two circuit elements, namely, digital filter 3601 ~nd memory 3602. Digital filter 3601 is implemented in the illustrative embodiment by ~ programmable sign~l processor especially developed for digital filter-tyPe applications re~uicing c~pil multiplications and additions and the caPability of miti~ating the effects of finite word length ~rithmetic. This programmable Pro~essor, h~weve~, has ~nlY
1024 addressable locations in memorY, which is the memory depicted by element 3602. ~igital filtar 3501 view, this space as RO~ and obtains its instructions ~nd data from this ROM space. On the other h~nd, PMU controller 3100 YieWs memorY 3502 as RA~. This allows P~U _ontroller 3100 to store numerous programs in its own R~M (depicted as memory 3150 in FIG. 1S), and by sele_ting one of the stored pr~grams and lo~ding it i~to DSP memory 3602, PMU
controller 3100 can effectivelY perform any necessary filtering or pr~c2ss1ng fun-tions. Pro~rams are downloaded from PMU contr~llec 3100 utilizing the add~ess ~nd data portions of bus 31002 and the rasults of processin~
~perations in ~ilter 3601 a~e P~ssei ba-k ~n the d~ta portion of bus 31002. Tntecnal communicati~n between filter 3601 and me~ry 3002 occ~rs over bus 36C11. Control signals, status bits, enable information, sat and reset _ondition,, and so forth ace co~municated between PMU
controller 3100 and DSP 3600 vi~ ~us 31002. Data from me~surement pr~ces;or 3500 (FIG. 17) on multiple la~d 35001 ~nd information for processor 3500 on lead 36002 link processor 3500 and DSP 3600. Bus 36001 ori~in~tin~ from DSP 3600 carries system reset and enable si~nals -~93'737 _ 82 controlling event monitors within DSP 3600 2.2.3~ PMU C~_tr~ E
PUU controller 310~ is a nicrocomPuter-based ,ystem als~ running under the s~me ~per~tin~ ,Y,te~ (OS) as DCN 140, LrS controller 2003 anl port controller 2200O In P~U contr~ller 3100, the tasks ~re ~s follows:a (a) PARALLEL DAT~ ta,k c~ntr~ls the tr~nsmission ~nd reception of messages over ParaIlel-oriented bus 20001 shown in EIG. 11. A messass is received by PMU
controller 3100 on an interrupt driven, bYta-by-byte basis.
~hen ~ full message has been received, ~S runs the PARALLEL
DATA task to deter~ine where th~ buffer me~ry storin~ the message is to be sent fo, processin~. rhe PRRALLEL DATA
ta~k ~lso form~ts full buffers for transmis,ion UP to L~S
sontroller 2000. The P~RALLEL DATA task is similar to PARALLEL OUTPU~ ta,k 11407 of FIG. 7 associatel with DCN 140.
(b) ADMINISTRATI0~ task runs several diagnostic functions, including the handling of illegal ins~ru-tion traDs from syst_m malfunctions ~nd ~eriodic software checks on critical, RAM-stored tables. This checking is implemented as ~ cyclical redundancy check ~nd is Performed in liau of hardware parity ~hecking.
~c) DUMP MEM task arr~nges for tr~nsmission of bloc~s of memory to I,TS controller 2~00 upon re~uest or up~n lete_tion of ~n error condition in the circuitry of PMU 2101.
(d) PMU task con~igures ~nd ener~izas the circuitry of PM'J 2101, collects data and focmat, the data for transmission UP the hierarchy. rhe Particulars of this task are now di,cu,sed with re~eren_e t~ the tests defined in Section 2.2.1c and in view of FI~S. 25 and 26.

rhe PMU task, re~esented by element 3101001 in FIG. 25, receives buf sr information as transmitted by the PARALLEL D~rA t~sk. Entries in the buffer s~eciFy which test is t~ be performed. The data specifies which of the ~3737 - 83 ~
manY possible test requests sum~arized in ~ection 2.2.1c is to be sele_te~; three such re~uests, depicted by elements 3101002-3101004 in ~IG. 25, include AC3rY, OCFEMF
and CN GRFV. In ea~h case, c~ntrol is pasaed to me~sursment cycle controller 31~ , which is l softw~re routine that causes the same basic functions to be performed each tim2, regar~less of the particul~r test request. The functions differ only in their h~ndlin~ and focmatting of the data returnad by DSP 3600.
IYeasurement cYcle controller 3101005 provides direct contcol ~f PMU circuitry as lepi~te~ in the structure chart of FIG~ 26. The ~aoftware oi _ontrolle~ 3101~05 operates seauentially fc~m left-to-right and top to bottom in FIG. 26. Each test request (31~1002~
3101004 of FIG. 25) calls this software as many times as is necessary to obtain the required measured -urrents on the loop under test. For instance, the OCFEMF test reauest requires ~y-le _ontroller 3101005 to operate three different times with a diff2rent cir^uit configuration each timeL The opec~ti~n of cycle c~ntr~llec 31~10~5 f~ each repetition is set forth in the followin~ with reference to FIG. 26~
First, a ,o-callel pcimitive tabLa, store~ in RON
of PMU controller 3100, is copied into a RAM copyspace via 2~ routine 31~1010. E~ch test reauest is ~omPletely specified by its primiti~e table. Parameters spe~ified in the table in~lu~e: settin~s for various system relays th~t configure, for exa~Ple, routing of ~IP ~nl RING through the apertures of the m~gnetic current sensing c~res; the type ~f signal to be me~sured (AC or DC); the D~P filtering algorithm that is to process me~sured dlta; and the reference f~eauency to be used _or synchron~us demodulation. In fact~ aPProximately forty bytes of memory ~re needed to c~mpletely specify a~-h PNU tast re~u2st. In addition, a dedicated memory area is establishsd into which variable data paraneters specified in the buffer sent from L~S controller 2noo may be storad. These v~ri~ble ~ lL93'73'7 _8~ -Farameters typically rePlace default pacameters built into e~-h pcimitive table. Thus, if the Primitive table has been defined t~ allow modification, routine 3101011 transfers the data from the dedicated memory area and makes the appro~ciate changes, if any. The A~ ~n~ ~r a~UCCe generators comprising circuit 3200 ~re deenergized to guacantee that ~veclo~ds d~ not cau~e PMU f~ res as the PMU configuration is changed. Likewise, a delay routine is entered after all relays are tr~nsferred t~ a ~uiascent state to allow for energy dissiPati~n.
Next, in preparation for the application ~f AC
voltage to the loop under test, dissipation resistors ~ithin soucce dcivecs 3301 and 3302 ~re selected an-l ~pplied to preclude voltase-overload failures. Then the entries in the pri~itive t~bla _orrespondin~ t~ mem~rY-mapped PeriPherals are seguentially written into memory by routine 3101016; in ~articular, the writes energize P~U
relays to establish the various measurement paths required of the Fresent test request. A_ and DC source generators within ci--uit 3200 are then en~bled by the next two routines. rha application of the test sign~l to the loop is no~ complete and tha remainin~ r~utines in measu~ement cycle controller 3101005 fo-us on collecting the measured data.
rhe v~rious channals throu~h dete_tor 34~3 an~
measurement controller 3500 uti1ized in processin~ detected -urrents each h~ve different responses to applied signals.
At system start-u~ these responses are measured and stored lS "calibr~te" values~ '~hen a loop is measured, the calibcate values ~f the channels must be taken into ~c-ount. rhe r~utine labelled 3101019 retrieves the values fc~m nemocy and coples these fa~tors for the channels into an array where they may be easily reference~ in order to ~djust the me~sured signals. In additi~n, coutine 3101020 initializes psuedo-gains which likewise must be accounted ~or when the final detected curcent values lre -al-ulated~

~33737 _ 85 -Next, routine 3101021 downloals the re~ui-ed processin~ pro~ram into DSP 3600. ~he downloadin~ occurs in three ~te~. First, after t~e bqsic proses,ing pro3cam is downloaded, i~easurement channel offsets ~re ~opied into an array from memory for ready reference. rhe offset _orrection is similar to th~ c~librat2 value adjustnent in that offsets will be used to convert actual measure~ents into corre_ted ~easurements. Ho~ever, offset corre~tion ~cc~rs via a slbtcaction operation wheraqs _allbrate factor qdjustment is via multiplicationO ~he second step involves sxamining the pcimitive table t~ determine if any parameters in the basic pro_essing progr~m ~re to be modified, such qs current thre,holds. If ,~, the third step makes the required ch~nges in primitive tqble values via routine 3101025~
~ he penultimate routine 31~1022 cuns the measurement cYcle. The samPle rate Passed to measurement controllec 350~ operates a system ~eqsurement timer. The cate is determined by a number of fqctors, includin3 the li~it~l filter to be used in D~P 3600 and the number of channels t~ be ~ea,~red. This cun ~y~la continues ~ntil the digital filter settles, the test ti~es ~ut or an interrupt ~ccurs. Assumin~ a s~ccessful conpletion, routine 3101022 collects the ~e~sured current d3ta from Da~ 3600 and makes reguired adjlstments. Finally, routine 3101026 resets P5U 2101, thereby completing the measu~ement cycLe.
~ ontrol of the circuitry of PMU 2101 then passes to the test request routine of FIG. 25 overseeing the test run. Dependin~ upon the stqse of operation, reconfi~urqtion may be initiated to -ollect additional data ~r the collectel data may be trqnsmitted to LTS
controller ~000.
~ s indicated in the above dis_ussion, calibration is an imPortant Part of the overall operation of PMU 2101.
Besides the three _alibrati~n procedures already identified, that is, (a) offset correction on ma~ne~ic ~L~L93737 current sensor cores, (b) ~ain factor valuas ~etermined fr~m ~pplying known, high leVel signals and measuring ~esponses ~nd t_) DC offsets datermined from responses without any input signals, one other calibc~tion procedure S ia utilize~. Oftentimes, the Dreci,e v~Lue; of the real ~nd ima~inary p~rts of the loop admittance provide valuable fault diagnosing information. ~o obtain these values, it is necessary to correct for Phase offsets within aub~Ystems 3300, 3400 and 3~00. Ph~se ~ffaets ~re determined by a three-step process. First, a terminatien within element 3310 of FIG. 20 having a kno~n Dha~e shift at the frequancy of interest is aPplied across the ~IP and RING leadsO Then the actual ph~se shift is measured. 3y comparing the expected phase shift to the measured Phase ahit, the phase shift through the v~rious _hannels may be determined. Di~ital signal generator 3200 n~Y then _ompensate for the i~dividu~l phase shifts by selecting appropriate table values fc~m the +-os 9 t~blss ~s the ~tarting p~int, ducing sign~l genec~tion.
2.2~4 LT~__r ;1_t,_~or~Es__~li,hin~_L_~_C~nne~ti~_ To describe the functions of the rem~ining LT~
_ircuits of FIG. 11 not exp~icitly caferan~~d ~c di,cusaed in some detail to this point, a typical sequence of operation, involvin~ most of these -ircuits i, described.
Variations on the seguencing presented ~re ~lso id2ntified where a~propri~te, and others m~y then be readily identified by those skilled in the ~rt in view of the foregoing discussion. The _ircuits to be discussed include talk ~ircuits 2301-2306, DDD circuit 2400, rin~ing distributor 250~, busy/spee_h detector 2600, trunk dialer 2650, equipment access network 2700, ports 2801 2816, sleeve le~d control unit 2950 and tr~cing tone aource 2~00. The ~perationa to be liacasaal inli_ate how a talk circuit is established between a Maintenance Center administr~tor and a customer.
~ cces~ to the customer's loop through EAN 2700 commenses with the transmission of the access request from 1~ ~3~37 LTS contr~llsr 2000 to port controller 2200, as Dlaborated upon in the precedin~ sections, Particularly ~ectlon 2.2.1a. As a first ste~ in the se~lence, part _~ntroller 2200 selects, from among the sixteen S ports 2801-2~15, a fr2e port having a test trunk 9401, .. 0, ~r 9416, ~nd a cor!esp~ndin~ slDeve leal 9417, ..., or 9432, associated with the telephone number ~f the customer'~ loop. (rrunk groups in ~ central office anviron~ent are associated with a subset of th~ set of 10 ~c_essible tele~hone numhers. rhus, anothec a-~e~ing possibility is that of having a s~it^hing arrangement to connect any port to a trunk from the trunk ~rouP servicing the desired telephone number. ~his adds another degree of freedom, but one that is not essential to the iDmediate 15 di,cussion.) F~r the sake of clarity of prasentation, it is presume~ th~t port 2~1, trunk p~ir 3401 and sleeve laad ~417 ,ati,fy the re~ue,t. A,su~in3 qls~ that the selected trunk pair does not exhibit hazard~us voltQ~es, the naxt atep i. t~ connect trunk dialec 2650 through 20 EAN 2700 t~ p~rt 2801. To understand the tachni~ue for accomplishin~ this, reference i, ma~e t~ FIG. 27.
As dePicted in FIG. 27, E~N 2700 is comprised of an array ~f 4x6 switch matrice, 271~-2713. Eocusin~ on matrix 2710, four horizontal leads 28010, ..., 28040 25 ~riginate from ports 2~3C1-2804, respectively; a~ch lead actually represents both th~ TIP and RING sDrvel by the _orrespondiny p~rt. The six vertical lead,, ql;o representin~ a pair of conductors, -onnect to the following six elements: PMU 2101; tracin~ tone s~urce 2300; talk 30 circuit 2801; the dial pulsing (DP) ~ortion of trunk dialer 2650; tha multifrequancy (MF) di~lin~ portion of dialer 2650; and busY~sPeech detector 2600. Th~ three laftmost vDrtic~l leads ara controlled by L control ssction 27~1 of EAN 2700, and e~ch lead forms one lead of a 35 unique, switchable crosspoint tL1-L3 for tha first vertical lead, L4-L6 for the secondr and so forth), the ~ther le~d in each case heing provila~ by on2 oE the four horizontal 1~9^~737 le~ds. Similarly, P control se_tion 2702 oDerltes -roaspoint, P1-P12 in matrix 2710. As FIG~ 27 lePicts, ~AN 2700 ia molula~ and ~ay be axpanded vertic~lly to include more Ports or horizontally to include more alements such as orecision measurements ~nit,, talk sicc~it, and ousy/sPee~h detactors. The main limitation on the expansion _har~_tecistics i, set by -onst~nts fixed within the softw~re design; these constant, are dacivei from ~emocy con,ider~ti~ns, timing c~nstcaints ~nd throu~h~ut cate.
Continuing with the examPle, it is supposed that di~l pulses must be applied to trunk 9401 f~r ~pec operation; this inrormation is tyoically stored in the mem~ry se-tion ~f p~rt contcoller 22~00 P _ontrol section 2702 then closes switch Point P1 in matrix 2710 to ~ccess the dial pulsing portion of lialer 2550. A ,ignal, typically a low impedance placed metallically ~-ross the trunk pair by dialer 2650, notifies the office switch that ~ialing is pl~nned. The o'fice e~ui~ment c2sP~nls, usu~lly with a TIP-RI~G revarsal9 to acknowledge the re~uest and then manipulate, the sleeve leai; the type ~f manipulation depends on the _entral office type. For in~tan_e, with one office type~ proYiding a hi~h ,leeve current ~eize, trunk 9401 ~nd prepares it to a-caPt di~l pulses.
Concurrent ~ith sleeve lead maniPul~tio~, P~rt controller 2200 loads dialer 2650, via bus 22Q01, with the telaphone numbec UPon receQtion of the rIP-RIN~ reversal;
once loaded, di~ling commences. At the completion of di~ling, anothec ~IP-RIN5 rever,al effected by the circuitry of trunk 9401 indicates that the customer's loop is no~ acce,sei in a bridgi~g oc m~nitor m~ie.
~ ince it is possible that the subscriber is utilizing the loop, crosspoint P2 i, opaned to ~isc~nnact dialer 2650 and crossQoint P3 is closed to atta_h busy/spee-h detactor 2600. Two basic test~ ace pecformed by detector 2600. First, the loop is checked for DC
voltage on the rIP and RING, If a loop is foun~ to be DC

~ ~L93'~37 busy, speech detection is performed by monitoring the line for bursts of energy that are chara_teristic of speech.
rhe statu, of the l~op is retur~ed t~ p~rt ~~nt~oller 2200.
If it is presumed that tne loop is idle, L~5 -ontroller 2000 is notified that port access is comPlete and detec~r 26~0 is disconnect~d. In addition, trunk parameters determined at system calibration, in-lu~ing trunk type, len~th and resistan-e~ are retu~ned ~ith the response messa~e.
Since a customer-~dmini,trqtor c~nne-tion involves q callback mode of opecation, ~n a_cesa utilizing an idle tqlk ciccuit 2301, ..., or 2306 i, Pro3ressing _oncurrently with port access. LrS controller 2000 -ommences this ~ccess directly via bus 20002. Dce~uming talk circuit 2301 is the idle talk circuit seized, the DDD
dialer circuit 240~ is connectel t~ talk -iccuit 2301 via channel 20003~ Talk circuit 2301 then draws dial tone over one of the DDD paira compri~in~ cable 23011 by ~la-ing a low imPedance across the P~ir. DDD dialer 2400~ which was loqded with the callback di~its when it was allocated, now dials or outpulses the number or the telephone to be used by the maintenance administrator. r~hen the administrator an~wecs the c~ll, the "0" digit (KEY ZER0) on the multifreguency pad is pushe~; in turn, talk circuit 2301 letects the fre~uencies assigne~ to the "0" digit and L~S
controller 2000 is aignalled ac_ordingly. LTS
controller 2000 in~icates t~ L -ontcol ,ection 2701 that crosspoint L3 is to be closed, thereby interconnecting port 2801 ~ith talk circuit 2301 (presu~ing 10~P ac~ess is _ompleted).
rhe customer maY now ~e conta_ted, an~ this is c_omplished by Lr~ controller 2000 sen~ing appropriate information to rin~ing distributor 2500, su-h ~s the particular talk circuit that re3uires ringlng ~nd the type ~f ringin3 (sin~le ~arty, two-p~rty, and so forth).
Ringin~ i, a~plied, in thi- case, through t~lk ~ircult 2301 by ringing distributor 250Q. C!1stomer ackn~wlelgment ~f 3'~3'~

the ringin~, typically by the receiver going off-hook, tripa ringing distributor 2500. T~lkin~ b~tte~y is supplied t~ the loop by talk ciccuit ~301 since a no-test trunk nor,n~lly doea not suoply DC t~ the l~p.
At this point in the description, the desired -ustomer-~dministr~tor cont~ct has been achieved. rO carry the example a few steps further, it may be that the _ustomer is asked to dial a certain digit so thqt a dial pulse analysis nay be effected. Th~ cr~sspoint L1 would be -l~sed to connect PMU 2101 to p~rt 2801 and cross~oint L3 would be opened for the dur~tion of the test.
If a -raftsperson is an~a~a~ in loo~ testing t a field location, it may have been the craftsperaon that was conta-ted by the above procodura, r~ther th n a customer.
If the craftsPerson requires a tracing tone, s~y for TIP-RING identification, crossp~int L2 is s~it~hed and tone source 290~ is now connected to the loop. rone is ~pplied from source 2900, and not PMU 2101, sin_e ~ ton2 usua ly is required for an extended duration and it is inefficient to rele~ate PMU 2101 to a low~level o~eration.
Once the tone is aPPlied~ the P.CCrSS/rEST t~sk of port _ontroller 2200 continues to monitor the status of the loop. When the craftsperson lo_ates the looP hlving the tone applied, a disconnect si~n~l c~n be generated by a rIP~RING shorting operation perform2d by th~t c~a~tsperson.
rhe monitocing task detects this st~te _han~e ~nd sends a "s~atus ch~n~ed" message U~ the hierarchy~ ~daver, the tone is maintained until anoth~r message is received to either DR~P the connection ~r u~til ~ time~ut ~_~ura. rhe status ch~nged message notifies the maintenance ~dministrator ~f tha on-going field activity and alarts the administrator that other test a-tivity may be f~rth_oming.
2.3 F_on__En~ (FE)_S _t~m The dascriPtion to this Point has focused, primarily, on the capabilities of D~N 1~0 and LTS's 160,161 within the MLT syst2m framework. Ono important subsystem, namely, the FE syste~ cludin~ FE _omputers 220~221 and '737 user interface devices 230,231, re~uires el~bor~tion~ This aspec~ of the lascriDtion focusas on how to ac~ess ~nd utilize the system capabilities des_ribad in the fore~oing sections.
~he M~T sYstem mu,t provide ooeration~l data to ~t least two types of users: Repair Servi_e ~ttend~nts tRSA), who are in ^ontact with the _ustomers, and RePair Service ~ureau (RSB) personnel, who analyze traubles and ~i,patch cepair cr~ftO The neels of these two lsers are ,imilar, but not ilentical~
rhe R~A re~uires aCC255 and test reguasts with r~pid responses an~ a tsst summ~ry that provides insi~ht to the reported trouble in a global waY. For ex~.~ple, is ~
trouble confirmed? ls it a central office trouble, a looP
tc~uble, ~ station troubl2~ rhe test shoull be performed ~utomatically when the trouble report is taken ~nd the results are needed promptly so that an appcopri te CePair commitment may be provided to the customer.
~he R~ needs det~ilel test results ~nd ths ~bilitY to Perform tests on dem~nd, sometimes while the repair craft i, at the loc~tion of the trouble. ~hus, the 2SB needs a menu of tests, some designed to duPlicate the tasts performad when the trouble wa, reoorted, and ~ome tailored to provile data on only a subset of all possible problems.
For b~th users, it is necessary t~ interpret the test results in vie-~ of recordei office, loop and stati~n or cu~tomer e~uipment, as extra_ted from storage computer 200, and to be somewhat tolerant of in-orcact or ~bsent re~ord d~ta.
~ hese diverse user requirements are satisfied by FE softwaca th~t can be divided into basically three ~ateg~ries: a terminal interfa_e process; a test interface ~rocess; and a tsst supervision and control pro-ess. These processes appe~r in each FE computer 220,221 and are ~rtitioned so that MLT related (DOW~) software communicat2, ~ith data base tUP) s~ftw~re ~-ros~ ~n 3'~37 interface boundary, as illu,trated pict~rially in FIG. 1.
rhe terminal inte~face pr~cesa re_eives test trqnsactions fr~m user terminala 230,231, performs d~ta validation, formats processing reguasts and forwards those re~uests t~ the test interface ~rocess an the FE c~puter actually -ontaining the Particular line record data. I~
the line recocd data is not on the ,ame FE _omputer the user is connected to~ the request is orwarded via hi~h speed parallel somnunicati~ns link 210 to the qpPropriate FE comPUter. This arrangement is i,n~ortant be_~use it an~bles organiz~tion of looP maintenance operati~ns in a manner that is reasonably independent of how the FE
computers are ~rganized.
rhe tast interface proces, obtain, the line re_~r~ datq fron the FE computec st~rageD rhe line rec~rd data and the ori~inal re~uest data are forw~rded to the test supervision and control process on the FE c~mQIlter chosen to Perform the test, that is, either the FE no~
_ontaini~g the line record ~ata or the FE ta which the user is connected. When the requested tests and analYsis are -ompleted, the cesults are ~orw~rde~ to the terminal interface process where they are formatted and presente~ to the user.
In orler to enable the user to inPut data and receive ontput in a uniform manner, ,evsrql tYpas of so-called masks may be callsd into vie~ of user ~3vice 230,231, tYPically a cathode r~y tuba (CR~) lisplay~
The disPlay below is an empty Trouble Verification (TV) m~sk which is u,ed by rePaic personnel for qll nocmql testing needs in an interactive testinq mode. rhe asterisks indicqte ~here a usec is to m~ke 3ntries.
rv EC* PRTR* REQ BY* CB* date,time S~ E:
rN* L#* CMT* CA* CO:
35 RE~* rEMP(F)* PR* OVER* OSP:
TERM:
The fields have the following meanings:

3~
_ 93 EC -- employee code.
PRTR - re,ults of a TV re~lest will al,o be ~ent t~ the designated printer.
REQ BY -- (Re~e,ted by) identifiec for printer output.
-B -- tCallback) normally a 1~ ligit teleph~ne number of the telephone accessible to the CRT user~ Many of the TV
re~uests (for instlnce, RING, rALK ~nd so f~rth to be set forth below) require a connection bet~een this sallback numbe~ and the ~ustomer's telephone e~uipment n~mbec;
pressing KEY-ZER0 ("0" on the keyPad) acknowledges the ans~er to the c~llback.
rN -- (Telephone Number) normally the entry in the rN field ia the nu,~ber ~f the equipment terminating the loop for which no-test access is re~uirel. However, it can also be used to specify the particular MDF trunk gC~UP f~r MDF
~^-ess.
REQ - (Request) ~ny valid rv request is entered into this field, i~ this field is blank, the last entry i~ u,ed as the current one.
CA -- (Cable) ~n optional entry that is useful for documentin~ the maskO An entry does not chqnge the line ~ecord inf~rm~tion. This field i, typi^ally e~ployed whenever it is believed the line record inf~rmation is inc~mplete or inacc1rate an~ a remin~er t~ thia eff2ct is desired, Particularly on a displa~ directed to the printer~
PR -- tPair) a field serving the same function ~s CA.
L# -- (Line number) this entry re~ers to a lins in the ,tatus section of the TV ma,k (disc~ssed be~). F~r axample, if a test was run on telephone number 362-5111, this numbec might be displayed as line 1 in the status section. rO test 362-5111 again, a "1" may be entered in this ~ield instead of typin~ the full phone num~er~ A L~
~lways overrides a TN entrYO
CMT -~ (C~mment) seven alphanumeric characters maY be entered for display on the status section of th~ mask qssociated with the telePh~ne nlmber. A tYpiC~ entry might be the repair~erson's name that is working on a loop '737 _ 9~
fault.
rEMP(F) -- (Te~per~ture-Fahrenh3it) ln entry is made here when resistive fault locating with L~C1 and LOC2 re~uests described below.
~VER -- (0verrile) certain line record data can be i~nored du~ing testing, as follows: C overrides C~ equipment;
~verrides outaide Plant (0SP) e~uip~ent; T ~verride, termination (TERM) e~uipment; P o~eccides servi_e protection (SP) rec~rds; Y ovecridea all ce^ords.
Moreover, there is the possibility of substituting e~uipment for C~, ~SP and TERM line rec~cd data.
Substitution is ac^omPlished by entering one of the follo~ing in ~VER fiela: C#, 0~ oc T#, Foc ex~mple, an "054" in the OVER field indicates an outside plant repe~ter (specifically ~n E5 repeat2r) ia pl~_ed at the C0 end of the loop. ~hese override options only temporarily ch~nge the line racord data for a single re~uest; no permanent alteration occurs.
~'tec the fields ~re fillea with the ~ppr~pri~te entries, the ~V request mask is transmittel, that is, sent to tne ass~ciated FE computer f~r proceasin~. For a request that keeps acceSs to a subscriber looP, the followin~ info~mation is returnad.
1. User entry area - The telephone number remains in the ~N area, and all othacs ~re bl~nk.
2. A line record are~ - rhe extracted line rec~r~ dat~ is sum~rized on the li~plaY-~he line racord information is enterQd into the are~s shown by a~, OE, CO, 0SP and TER~ in ~he rv mask ~iaplayel ab~ve, presuming a 10 iigit number in the rN field. ~he C~, OSP
qnd TER~ field, h~ve been describe~ ~bove ~ith cespect to OVER. SW (Switch) refers to the CO switching egUiPment type. T;~e possibilities in_lu~e: SXS (Step by-step);
XBAR-1 and XBAR-5 (Crossbar offices); ESS-1, ESS-2, ESS-3, ESS-5 (Electronic switching offices), P~N~L; and DMS10 (Digital a~itch)~ OE tOriginatin~ e~uipment) refers to the loc~tion of the subscriber looP at the awit^h~
.

1~ 3 ,,3 7;~ 7 rhe entries in the CO, OSP an~ T~RM ~raaa ace especially imPortant because tha equiPment they represent influence the ~tc~e of ths MLr ,Y,tem ta~ts. Whenever a tes~ is m~le on a line with spe_ial equipment ~n it, that equipment is taken into account whe~ analyzing results, For example, if a test is effected on a loop th~t hls a Loop Signalin~ Extender, a DC resistance TIP-to-RI~G of 30K ohms or hi~her is expected. Normally, q value of resistance this low would indicqte q TIP-RING short, and this would be re~orted to the uaer via a reaults se~tion (describe~ below). In this situation, hoNever, the message reports a good loop ~iven the s~eci~l e~uipi~ent. The entry LOOP aIG EXTENDER is entered in the CO qre~ to explain why the DC resistan~e in the detailsd results section is low.
Because of thia ca~ability, the MLT system ql~,ith~s are considered to be adaPtive in nature in that test signatures of numerous e~uipment types and locations qre ~ccounted for during testing and presentation of output information to th~ user.
3~ Status section -- This section provides new data on the di,play and it app~qr, only if ~t least one telephone number is presently being accesse~. The information is shown as a numbeced line under these heqdings:
TN MDF STATUS CB TIME FR CA/PR CMT
rhe headings have the following definition~:
TN -- (TelePhone Number) as filled-in by the user in making the re~lest.
~DF -- (M~in Distributing Frame) uPon a ~DF access to a tcunk, the number identifying the trunk to the frame ~ttendant is returned.
STATUS -- some rv requests cemain on a looP for ~ prolonged period, but do not require q callback Dath. Thay a~ay ~n the looP for a ~re~etermined period or until removel bY the user. One nf the following entries is retucned: TONE or rONE~ if that ra~uest was mqde; 1aIDED or 2,IDED if a LOC
re~uest was enter2d and the bad ~air has a one-sided or t737 _ 96 -two-sided resistive fault, resPectively; GOODPR or REFPR if 3 request of the type LOCGP is made and a g~d paic or mzrginally good Pair is located, respectively; (blank) for all other rv ce~ue,ts.
C~ -- (Callback) on a callb~ck between a subscriber's telephone number and the administrator or user's test position, a remindar is retQrned to indicate a l~ng-tec~
conne~tion is m~intained and tha request which established the connection. For instance, such entrie~ as rALK for a rAL~ or RING reaue~t or MON for a M~N request ~r a RING
re~uest to a busy loop are possible entries.
~IME -- the numbec of minutes elapsed sinca lo~p acces, is dis~layed, or if TO~E is re3uested, the number of minutes since the tone has been applied is ,hown.
FR -- (Fr~me) the telephone number of the fcame serving the nu~bec pl~~ad in the TV are~.
~A/PR -- ~Cable/Pair) refle_ts information entered by the user prior to transmission of TV re~uest.
CMT -- (Co~ment) the comment entered on the last request to this status line is displayed.
~ ha ,tatu~ secti~n can hoLd up t~ five a--esses at a time. Drop~ing of a loop access causes an automatic renumbering of status lines following the dropped looP.
4. Results section -- The results for the p~rti_ular rv reguest are displ~yed. ~he testing accomplishad bY the M~T system varies as a function of the request. rhe r2quests may be classified and briefly described as follows:
~a) Infocnati~n Ra~uests HELP Pr~vides a list of ~ll rv requests (REQ)? Provides a description of ~hatever re~uest is substituted for REQ
INFO Provides general inform~tion su_h ~s ~ra~e ~hone nu~bers, as,i~n~ent phone numbers, ~nd so forth ~ R(~) Pernit~ transfer of ~ork between user devices (b) MDF Re3uests .~g~ 3 MDF Access an MDF trunk for subae~uent re~uests MDF(GR) A-~ess ~ trunk from a certain MDF trunk group ~DF(#) ~C^2SS a sPecific MDF trunk (c) Test Re~uests FULL Pecforma a staniard test -aecies on inside and outside portions of the loop L00P Performs the st~ndard test series on the ~utside portion ~nly CO Performs tests on the Central 0fice 1~ QUICK Pecfor~s a guick te-at seriea th~t measures AC and DC characteristics and loop length RINGER Identifies the number and confi~ucation of st~ndard ringers on ths loop SO~K Identifies swin~ing reaistance _onlitions ~d) Callback Requests RING Rin~ a line R(#) Rin~ a specifi- party on a multiparty line T Talk over the subscriber's loop MON Monitor a subscribe~'s loop CALL tlake a call using the subscriber's line circuit (e) Subsc~ibec Interaction Re~uests DIaL Test a subscriber~s rotary dial REV Identify inwband si~naling instrument for polarity revers~ls TT Tes~ subscriberls in-band signalin~ ~ad (f) Craft Interaction Requesta TONE Pl~ces a metallic tone on a looP
for Pair identification ~ONE~ Same as TONE with incre~sed amplitude tone TONECA Pla~es a tone longitudinally on looP
LOOK Nonitor for an intentional fault LOCATE Initiates the resistive fault meaaurement strategy; recom~end~
sin~le- or double-sided procedure LOC1 Detar~ines distlnca to ~ sin~le-sil~d f~ult LOC2 Determines distance to a double-sided fault LCCGP Verifies the condition ~f a ~oo~ pair 73~

fo~ double-sid2d f~lt i3ts_ti~n (g) Drop~eep Access Requests X ~r~p all testin~ e~uipment fro~ lo~p XCB Dr~ a callback path XTONE Drop a tone from a looo KEEP Extend timeout ~f a no-t2st or MDF tcunk access (h) Coin Requests COIN Parform a FULL test series on ~ coin looP
~SET Che-k totalizer and rel~y in coin s2t CHONE Home coin totalizer CCOL Operata coin relay to colle_t c~ins CRET Operate coin relay to return coins LRM Meaaure loop reaist~nce ~f coin lo~p GRM Me~sure ground resistancs of coin loop Rathec than describin~ ea-h of tha ra~ueats in detail/ one request is selected as exempl~ry and the user-re3ue,t intera~ti~n is disc~sse~ ~elo~. Appli-~bility ~f this description to the other TV requests~ Particul rly in view of tha hi~h-level language program listing, pcesented later, ~ill be a~p~rent to one possessing ordinary skill in the art.
rhe ~articular reguest chosen to exempiify the TV
ca~uests i, the FULL test regueat. rhis teat re~ueat provides a series of tests to comPrehensively analyze the entire teleph3ne l~op of a particular slbsc~ibeci It pro~ides detail3d results and a su~mary o~ the condition of both the inside ~central office) and ~utsilP p~rti~ns of the looP under test. rhe following tests, brieflY
~escribed in Sa~ti~n 2.2.1_, ara completed: OCFENF, DC3TY, AC3TY, BAL, THERM, DTA, SOAK, RCNT and ~OH_rES~.
rhe display for the FULL raguest including the status and results section, has the following format:
rv E~ PRTR RE~ BY CB lata,tim2 TN MDF STATUS CB TIME FR CA/PR CMT
1. 993555~98 0 555-7432 534-7611 TN 9995553898 SW:SXS OE:8829-128 .~ll9~3~
_ 99 _ REQ L~ CMT CA~0:
TE~P(F) PRO~P:
FULL TERM:SIN~ PnRrY
VER. 22: H~RD ~HORr T-R

5 CRAFT: DC ~I5~ MLT:DC SIG. AC SIG.
KO~S VOLT~ KOHMS VO~T~ KO~IMS
7 T-R 7.76 T-R 10 ~-R
1750 0 ~-G 3500 0 ~-G 550 r-R
1750 0 R-~ 3500 0 R-G 560 ~-G

~0 CENTRAL OFFICE
LINE CKr OK
DIAL T~NE OK
~ he nawly apPended areas form the rea~lts section. In this section, it is indicated th~t there is a short on the loop~ This c~nclusion is praa--ntsl with the qid of a VER ~verification) code num~er (22 is this case) ~nd the summary message HARD SH~RT. The MLr system has numerous VER codes and summary messages available for sela-tion ~nd display to help in diagnosing any trouble~
Besides the brief summary area, a d2t~iled results area lisplays all the test results. Here, a low T-R DC
cesistance value of about 7 kohms c~Used the H~RD SHORT
lia~n~sis 9 The T-G and R-G DC resistan~e v~lues are hi~h so there is no ~round conaition. The AC si~nat~re is typical of a st~ndard telephone providing the end-of-line terminati~n, a~ no fault c~ndition is dete~ted by the ~C
portion of the test. All DC and AC voltages are zero inlic~tin~ that there is not a _ross with ~nother voltagq source. Finally, the central office e~uipm2nt is not f~ulted- No l~op length, balan-e O! rin~ee inf~rm~tion is displayed since a-surate results cannot be produced ~or a shorted line ~or other faults which mask the teats). If these values were dis~layed, they would appear in the area to the ri~ht ~f the CENTRAL OFFICE area9

Claims (3)

Claims

1. In a communication system comprising:
a plurality of remote wire line centers, each terminating a plurality of loops and associated customer equipments;
a centralized facility for storing data concerning the loops and associated customer equipment in each wire line center; and an arrangement in the centralized facility for analyzing data from the wire line centers, CHARACTERIZED IN THAT
the remote wire line centers obtain and analyze the data from the loops and forward the results to the centralized facility over a switched transmission network.

2. In a communication system comprising a plurality of wire centers each having test trunks connectable to customer loops and customer equipment served by the wire centers, a system for accessing the loops comprising a plurality of autonomous computers arranged for intercomputer communication and including interfaces for receiving requests from system users and for generating corresponding messages, a plurality of stored program control systems, each being collocated with one of the wire centers, each of the control systems being arranged to access the loops through corresponding portions of the test trunks, and a network for transferring each of the messages from the computers to a corresponding one of the control systems, each of the interfaces including circuitry for establishing communication paths over the external communication network terminating at each of the interfaces, and the control systems being arranged to access the interface circuitry over the external network via trunks originating at the wire centers, thereby providing a connection for interactive communication.

3. The system as recited in claim 2 further comprising arrangements for simultaneously testing a plurality of loops served by each of the wire centers.