CA1054258A - Communication line test apparatus - Google Patents
Communication line test apparatusInfo
- Publication number
- CA1054258A CA1054258A CA241,754A CA241754A CA1054258A CA 1054258 A CA1054258 A CA 1054258A CA 241754 A CA241754 A CA 241754A CA 1054258 A CA1054258 A CA 1054258A
- Authority
- CA
- Canada
- Prior art keywords
- digital
- analog
- analog signal
- communication channel
- signals
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/22—Arrangements for supervision, monitoring or testing
- H04M3/26—Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
- H04M3/28—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
- H04M3/32—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for lines between exchanges
Abstract
ABSTRACT OF THE DISCLOSURE
A communications line under test intercouples programmable local units, one of which transmits an analog waveform to the other in response to digital control signals received from a computer.
The receiving programmable local unit transmits a digital signal to the computer representative of the received analog signal to thereby enable the computer to determine transmission characteris-tics of the communications line intercoupling the programmable local units.
A communications line under test intercouples programmable local units, one of which transmits an analog waveform to the other in response to digital control signals received from a computer.
The receiving programmable local unit transmits a digital signal to the computer representative of the received analog signal to thereby enable the computer to determine transmission characteris-tics of the communications line intercoupling the programmable local units.
Description
~c~54258 A NOR P02 BACKG:ROUND OF THE INVENTION
CH/ ck lljl9/74 The present invention reIates' in general ~o program~
mable me~suxing and more particularly concerns noveI apparatus and techniques for rapidly and automatically testing the trans-mission characteristics of a communications channel that may be remote from a central computer through measuring analog test sîgnals transmitted over the channel while communications between the central computer and the'terminal points of the channel under test are'through reIiable digital signals to enable the digital computer to readily determine'the transmission characteristics of the communications channel under testO
~ A typical prior art approach to checking a communications j channeI: comprises a local computer in a closed loop including the communications channel to be tested. Having a digital computer for each communications link is costly, for a typical communica-, tions system has many linksO
Accordingly, it is an important object of this invention to pro~îde apparatus and techniques that facilitates' using one digital computer to automatically'measure transmission charac-terist:ics of a number of communication links in a commun:ications systemO
It is a further object of the invention to achieve`one or more of the preceding objects with'programmable local units that are reIatively inexpensive and reliable.
It is a further object of the invention to achieve one or more'of the preceding objects with'programmable local units characterized by a high degree of flexibility and capable o functioning both to receive and transmit test signal waveforms and to accept digital command signals from the computer and provide digital signals to the computer relevant to the'programmable measurements being madeO
It is a further object of the invention to provide novel ~2~
A ~OR P02 apparatus-and techniques,for providing a wide variety of waveforms.
/74 It is a further ob~ect of the invention to provide a programmable local unit having both a digital signal input and a digital signal output for communication with a digital computer and an analog input and analog output for exchanging signals with a communication link to be testedO
It is still a further object of the invention to provide noveI shift regist-er techniques for generating analog waveformsO
It is still a further object of the invention to provide sh~ft register techniques,for converting a received analog signal into corresponding digital signals.
It is still a further object of the'invention to achieve one or more o the preceding objects while'controlling signal gain to keep signal levels so as to obtain substantially maximum resolution.
SUMMARY OF THE INVENTION
',~ According to the'invention, there is a central digital computer that transmits digital signals to a programmabIe local , unit at an end of a communication channel to be'tes.ted. A
programmable'local unit includes means responsive'to the.'digital ' signal, from the digital: c'omputer for providing an analog signal `:
~ waveform for transmission over the communieation channel under : test and means responsive'to the received test analog signal transmitted oYer the`commun:ications link for converting the ,~ recei.ved signal into a rep.resentative digital signal that is transmitted to the digital computer to enable the'latter to determ,ine'the transmission characteristics of the communications link'under test.
A local unit according to the invention includes gener-ator buffer means o~ storing a sequence of digital numbers : representative of a signal waveform to be transmitted over the communicationslink to be'tested, digital-to-analog converting means -3~
105~Z58 A NOR P02 coupled to the generator buffer'means for converting the digital /74 signal provided by the generator buffer means into a corresponding analog signal and output level control means for controlling the amplitude'of the latter analog signal to a predetermined level for transmission over the communications link to be tested that is deIivered to line interface means for exchanging signals with the local unit and the communications link.under test. The local unit also includes input level control means for .controlling the amplitude of a signal provided by the'communications link under test to a predetermined level, analog-to-digital converting means responsive to the latter signal of controlled le~el for providing a representative digital signal, and receiving buffer means for storing the latter digital signals as a sequence of digital numbers representatîve of the signal received over the communications link for transmission to the'remote'computerO The local unit also in-cludes microprocessor control means for controlling the leveIs, the'conversions between analog and digital form and receiving ap~
propriate instructions from the remote computer to load a desired signal waveform into the'generator buffer means and to unload a digital representation of the received waveform from the receiving buffer'means for tra,nsmission back to the remote computerO
A,feature'of the local unit is that it has means for exchanging digital signals representative of analog signal wave-forms transmitted over a communications link under test and means for exchànging these analog signal waveforms with the comm~nications lînk under test, A more specific feature of the invention is the.form of the generator and receiving buffer means. Each t~pically comprises a plurality of shift registers that exchange'digital number signals representative of analog signal waveforms in paralleI at one end and exchange digital number signals serially representative of an analog signal waveform at the other end.
lOS4ZSB
A NOR P02 Still another feature of the invention is the.'use of CH/ck :11/-1~/74 digital automatic gain control'means..~or adjusting. the input level to obtain maximum reso.lution of the analog signal with'the available bits for digital conversion, the means inc.luding a swîtched gain amplifier with negligible phase shift.
Numerous other fea.tures, objects and advantages of the înventîon will become'apparent from the following specification when read in connectIon with the'accompanying drawing in whîch:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram illustrating the logical arrangement of a system according to the invention; and FIG. 2.is a block diagram îllustrating the logîcal arrangement of a local unit according to the invention, DET~ILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference'now to the'drawing and more particularly FIG. 1 thereof, there îs shown a block diagram illustrating the : log.ical arrangement of a system according to the'inventionO A
central office 11 inc.ludes a central computer, such as a Digital A~. (T~) memory ' ~' Equipment Corporation PDP-8Elhavîng a 16K bit core/and disc memory coupled.to a conventional teIetypewriter 13 for accepting informa-tion on tests to be made'and printing out the'results.of the test.
Central computer 12 is coupled to teIephone lînes through line interface 14, such as BeIl 2Q2. data sets. TeIephone lines 15 and 16 intercouple'central office line interface 14.wîth local units 17 and 18, respectîveIy, inte.r.coupled by line 21.under test.
In the exa,m,ple'.local unît 17 is indicated as functioning as a generator that transmits analog waveform 22.over line 21 to local unit 18 functioning as a receiving unit for the'analog waveform 22. However, it is within the principles of the inven-tion for each'local unit to function as one'or both of transmitting and receîving-unitsO For examp:le, it is within the principles of the invention to transmit the analog waveform 22:f~om remote ~5~
A NOR P02 site number 1 to remote site number 2 and back to remote site /74 number 1 ~ith local unit 17 functioning as bo.th. transmitter and receiver so that line 21 could be tested with but a single communi-cation link between central office 11 and remote site number 1.
Having discussed the physical arrangement of a system according to the invention, its mode of operation will now be discussed. An operator enters on teletype 13 information on the test to be performed, the line to be tested and the local unit or units to be used in the tests. The test to be performed may be those useful in checking a particular communications link.
For example, typical measurements made on a teIephone line include single tone interference loss, frequency shift, phase jitter,/and C-notched noise using a 1015.625Hz taneO Other measurements typically made include those of second and third intermodulation distortions using the sum of three tones, attenuation and delay distortions using a spectrum filling signal and C-message noise using a quiet termina-tionO The specific tests are not a part of the invention and are by way of example in connection with illustrating the best mode now contemplated for practicing the inventionO
Typically, the test might be a frequency response tes~
: to de.termine attenuation distortion and deIay distortion at specified impedance levels, typically 600 ohms. With local unit 17 identified as the generator and local unit 18 identified as the receiving unit, each receives digital signals over lines 15 and 16, respectiveIy, that readies each to perform its desired function. Thus, local unit 17 proceeds to transmit a spectrum of tones o~er line 21 that is received by local unit 18 which then transmits a digital representation o~ the signal waveform over line 16 to central computer 12:through interface 14 so that central 30 computer 12 may process the. digital representation ~nd print out on teIetype 13 test results, typically listing each frequency of the transmitted spectr~m followed by the attenuation at that ~6~
1054Z58 `
A NOR P02 frequency and the deIay at that frequency. The'specific techniques, /74 such'as fast ~ourier tr~nsform methods, for processing digital representations of measurements received at different frequencies to print out a frequency response are well-known in the digital computer art, are not a part of the invention and are not described in detail herein so as to avoid obscuring the'principles-of the invention.
In a typical requency response measurement the local unit transmits digital samples of the received waveform to the central computer representative of a voltage'waveform as a function of time in the time'domain similar to what would be observed using an oscilloscope, The central computer uses a Fast Fourier Transform algorithm to convert the samples to amplitude and phase as a function of frequency in the ~requency domain to represent the'received waveform by its spectral components, The computer subtracts the'received amplitude from the'transmitted amplitude'at each frequency to determine attenua-tion and takes the derivative'of the phase'response'with'respect to frequency to determine'deIay. These methods are'weIl-known in the digital signal analysis field~
- Referring to FIGo 2 ~ there is shown a block diagram illustrating the'logical arrangement of an exemplary embodiment of a local unit according to the invention. The local unit includes a 1200 baud half duplex modem 23 for interfacing with the teIephone lines to the central office, such'as 15 or 16, for exchanging digital data signals therewith'at a 1200 baud rate. A micro-process-or control means 24 exchanges digital data with modem 23 and signals with the other eIements of the local unitO The local unit includes a generator buffer 25 for receiving a sequence of digital numbers representative'of a waveform to be tran'smitted oyer test line 21~ a digital-to-analog converter 26 for converting the sequence of digital numbers provided by generator buffer 25 -7~
~05~258;
A NOR P02 and an output filter,output level controller 27 for controlling ~/74 the level of the analog signal for transmission over test line 21 and a line interface 30 for coupling the tes't signal from out-put leveI controller 27 to line 21 and coupling ~ si~nal received from line 21 to input filter and input level controller 31 in the receiving branch of the local control unit. The receiving portion of the local unit also includes an analog-to-digital converter 32.for converting the received analog signal of controlled leveI into a sequence of digital number signals that are'entered parallelly in receiving buffer 33~ Receiving buffer.33 provides a sequence'of digital numbers to the central office through modem 23 under the control of microprocessor control means 24.
The local unit may also include a general purpose bus 34 for exchanging data with local apparatus at the location of the local control unit, such as a local computer, keyboard/display, digital.voltmeter, other instruments or RAM or ROM storage means.
Having briefly described the physical arrangement of the local unit, its mode of operation will now be discussed.
12QO baud half duplex modem 23 is capable of interfacing with any computer and receives commands and generator sequences from the computer for transmission over test line 21 while sending results of commands and samples in digital form of a test signal received - on test line 21 to the'central office computerO Preferably these digital signals are in ASCII code with'odd parity.
: Microprocessor control means 24, typically an Intel MCS-4 integrated circuit, accepts commands from modem 23 or general purpose bus 34 and decodes and executes these commands.
~ list of the commands are set forth below~ The specific means for decoding and executing commands are weIl-known in the art and not described in detail to avoid obscuring the'principles of the invention.
~8 A NOR P02 When the local unit is functioning in the'transmit mode, /:74 generator bufer 25, typ.ically capable of storing 512:12-bit digital ~ords, receives a sequence of 12-bit words through control means 24 and modem 23, the digital data entering in byte form.
Microprocessor control means 24 then causes generator buffer 25 to be cycled typically at an'8000 Hz rate to provide paralleI ac-cess to each'l2-bit digital number signal for conversion by digital-to-analog converter 26 into a representative amplitude level that is controlled by output level controller 27 under the control of microprocessor. control means 24 to provide on line 21 the test signal. ' ~ For testing typical telephone lines the filter portion : Of output le~el-controller ' and filter 27 is typically flat to.3000 Hz,.3dB down at 3200 Hz and 60dB down at 8000 Hz,. the . cycling rate.
Line interface 31 may include switching relays for ef-fecting appropriate'connections ta transmit terminal-2IA and re-ceive'terminal 2IB of line'21. For example,' the switching relays ~ay switch'in an appropriate'terminating impedance,' typically 600 ~ 2Q or ~00 ohms, a quiet termination for measuring quiescent noise or .~.'' effect a loop around wherein the'test signal is received on input with less or gain in level ~-~ 21B and retran'smitted on output 2LA/so that all communication with ~ the'central office compute-r may be'essentially with'one'local unit.
';. ~ A received signal thr~ugh line interface 31 is typically applied to input filter and level controller 3I, typically filtered, . ~ in accordance with'similar transmission characteristics. described above in connection with' outp.ut.level controller and filter 270 Level controller.31 typically amplifies the received input signal to a maximum of 60dB in 4dB increments to insure better than ll-b.it resolution~ This amplification is preferably accomplished automatically so that the maximum level provided at the'input to analog~to~digital: con~erter.32..corresponds to ~9_ ~0542S8 A NOR P02 the largest value of a 12~bit binary numberO This may rapidly ll`/L5/74 be accomplished automatically by initially setting. the`amplifica-tion at 60dB and decreasing the ampliication in steps untiI this maximum digital number value is provided by analog-to-digital con-verter 320 Analog-to-digital converter 32 converts the filtered input signal into 12-bit samples at an 8000 ~z rate that are stored in receiving buffer.33. Microprocess-or control means 24 then effects the transfer of the digital numbers stored in receiving buffer 33 in byte form through modem 23 to the central office computer~ Since the central office computer then has a digital representation of both the transmitted test signal and the corresponding received signal, well-known techniques may be : used to digitally evaluate transmission characteristics of the line, such as frequency response, distortion and noise leveI. The specific techniques for performing these evaluations digitally are well-known in the digital computer art, are not a part of this invention and are not described in detail here to avoid obscuring the principles of the invention, There follows a list of typical commands to the local unit-and responses from the local unit together with appropriate . designations on a conventional keyboard that may be used for desig-nating these commands, the nature of the command and whether it is an immediate or string command. The significance of the commands will then be described.
COMM~DS
Load Waveform 1 Two Character Immediate ~s~Second Character = From Where to Load .Assigned Wher~ s - M Modem R Receiver Buffer 0~15 ROM/R~M On GP Bu.s Send Samples 2. Two Character I~mediate Second Character = Where to Send Assigned Where s - M Modem T Transmitter Buffer 0-15 ROM/RAM on GP Bus lOS4Z58 A NOR P02 Start String 3 One Character Immediate CH/ck llllg!74 String Enable 4 One Character Immediate Retransmit 5 One Character Immediate Conditional End I/0 6 One Character Immedia~e Identify 7 One Character Immediate Stop Generator = One Character Immediate Self Test ~ One Character Immediate Bus Clear ? One Character Immediate Start I/0 CR Two Character Immediate Second Character = Local Unit Address End I/0 NAK(ERR) One Character Immediate ~bort BS (FE? One Character Immediate Set Output Level 0 Two Character String Second Character = Six Bit ASCII Word Giving Amount to Decrease Output From MAXIMUM.
(Most Significant Bit) MSB= ~32DB, -16DB, -8DB, -4DB, -2DB, -lDB = LSB (Least Significant Bit) Generate G Two Character String Second Character = Six Bit ASCII Word Giving Number of Sample Periods as Length of Generate Time -@ = Generate IndefiniteIy Adjust AGC A One Character String Set Input Gain I Two Character String Second Character = Six Bit ASCII Word Giving Input Gain MSB = ~3~DB, +16DB, +8DB, +4DB, X, X = LSB
Sam~le S One Character String Line:Configuration L Two Character String Second Character = Six Bit ASCII Giving New Line Configuration MSB= Input ReIay, Bridge, Loop? 600~9.00SZ, Output Relay, Modem = LSB
Delay D Two Character String Second Character = Six Bit ASCII Giving Number of Sample Periods to DeIay @ = ~o Delay End String E One Character String Interxupt M Two Character String Second Character - Data For GP Bus With IRT
Acti~e Universal Bus Command U Two Character String Second Character = Least Significant Five Bits Are Unlversal Bus Command -~os4~ss A NOR P02 Begin Bus Data B One Character String /74 Finish Bus Data ~ One Character String The commands are classified as immediate and string.
An immediate com~and is one that is executed immediately upon receipt by the local unit. String commands are stored in random access memory comprising'microprocessor control means 24 and executed sequentially after the End I/O command~
We turn now to a discussion of the specific commands.
The LOAD ~AYEFORM command is typically designated by pressing the 1 key followed by a second character designating from where'to load. Thus, pressing M selects the modem as the source of a digital representation of the test waveform for storage in generator buffer 25, pressing R selects receiver buffer 33 as the source'and pressing numbered keys from 0-15 select specific ones of waveforms that may be locally stored in a random access memory or read only memory at the location of the local unit through general purpose bus 34.
The'SEND SAMPLES command is selected by pressing 2 fol-lowed by a character designating where to send the samples, M for the''modem, T for the generator buffer 25 and 0-15 for a designated one'of random access or read only memories through general purpose bus 34.
Pressing 3 designates the START STRING COMMAND to cause the'local unit to store'the following commands as string commandsO
Pressing 4 selects the'STRING ENABLE command to condition the local unit to enable a previously stored string.
Pressing 5 causes the'local unit to retransmit its last response'to the computer, Pressing 6 implements CONDITIONAL END I/O whereby digital communic~tion stops and no string is executed, Pxessing 7 implements IDENTIFY for directing the local unit to command devices on the GP Bus to identify th~emselves.
1054Z58 f A NOR P02 Pressing = implements the STOP GENERATOR command for CH/ck 11/-19/74 ending the transmission of a test signalO
Pressing > implements~the SELF TEST command whereby the local unit may perform a self testing routine to insure proper operation.
Pressing ? impIements BUS CLEAR command to terminate the'data transmission on the GP bus, Pressing CR followed by a local unit address designation im~lements the START I/O command for establishing communication with the local unit to receive'appropriate commands~
Pressing NAK implements the END I/O comm~nd for ending this exchange and executing any enabled string.
Pressing BS implements the ABORT command which causes the local unit to abort the immediate command then being executed.
Pressing O followed by a second character that is a 6-bit ASCII word designating the amount to decrease the output from MAXIM~M by -32, ~16, ~8, ~4, ~2 and ~lDB from t~e most signi-fîcant ta the least significant bit, respectively, and effect the setting of output level controller 27 accordingly.
Pressing G followed by a 6-bit ASCII word giving the numbe~ of sample'periods as the length of the generation time effects the'GENERATE string command that causes the waveform stored in generator buffer 25 to be provided on test line 21 for the designated period, pressing @ following G causing the'waveform to be generated indefinitely until a stop generator command, Pressing A seIects the'A~C string command that causes the lcvel setting of leveI controller 31 to maximize'the'resolution as described above~ Pressing I followed by a second character in 6-bit ASCII im~lements the SET INPUT GAIN command that sets the'level of input level controller 31 to a level designated by the'ollowing ASCII word with the'sixth through third bits designating *32DB, ~16DB, ~8DB and ~4DB increments of gain, -~054258 Pressing S im~lements the SAMPLE string command which causes the'received signal to be'converted into digital form and stored in receiver buffer 33r Pressing L followed by a six-bit ASCII character imple-ments the'LlNE CONFIGURATION c'ommand to control the relays in line interface.3I to estabIish'the'various:connections and terminations described above.
Pressing D followed by a second character in:6-bit ASCII code'identifies a number of sam~le'periods to deIay before executing the next string command while'pressing @ produces no delay, : Pressing E implements the END STRING command, thereby signifying the end of a group of string commands and returning the'local unit to imm.ediate mode.' Pressing M followed by a second character addresses devi-ces 1 ~
/ o.n the general purpose'bus with'IRT activeO' .. Pressing U followed by a second character implements an:UNIVERSAL BUS COMWAND for the'general purpose bus.34. Pressing B im~lements- the BEGIN BUS DATA as a one character string to cause : ~20 the following data in the string to be'applied to the general: purpose'bus.34, and pressing a implements the'FINISH BUS DATA
command that is a one'character string for terminating the transfer of the data oYer the'general purpose'bus.34.
The'local unit may also transmit replies which'may be observed on the'teletype at thé central stationO Observation of ~ indicates a transmission ~error, such'as a parity error, an overrun or framing errorO Obs'ervation of >> indicates a mode`
' error whereby a string command was received in the'immediate`mode.
Obsexvation of # signifies an illegal command, such as an unassigned.command, uneq.ual characters or loss of carrierO ' Observation of $.indicates that the'assigned command is done, such'as sampling or self-test. 'Obse.rvat.ion % indicates fail, such : -14-~054Z58 as the'sampler.ove.rloaded or the seIf-test failed.
Observation of & signifies service .re~ue.st, indicating that the`general purpose'bus needs ser~ice.
Each local unit has a~unique address which'allows more than one'unit to share a single l2QO baud line'to the central computer 12. A START I/O comm~nd signal followed by an address : signal initiates a command sequence'to the'local unit addressed.The addressed local unit executes immediate'commands immediately upon receipt without transmission errors. The string commands are : 10 stored in xandom access memory.comprising microprocessor: control m.eans 24 and executed after receipt of an END I/O command signal.
:'~ Either an END I/O or CONDITIONAL END I/O command signal must te'rminate'a command sequence'before a different local unit may : be'addressed, the latter: command signal not causing exe~ution of string. commands. Each local unit is in the'immediate''mode at the r beginning of a command sequence The'START STRING command signal alerts the addressed local unit that string commands follow.
The EN.D STRING command signal returns the.'unit to the'immediate de.
20 There is set forth'beIow a typical immediate'command format indicating the exchanges between the central computer and the Iocal unit.
CQNPUTER GENERAT'O.R LO.~AL'UNIT
START I~O
ADDRESS
~ : ADDRESS
LOAD WAYEFOg~ -+ LOAD WAYEFORM
MQDEM
+ ~ODEM
512 12~BIT WORDS
CHECKSUM PARITY.
~15-~05~258 k COMPUTER GENERATOR LOCAL UNIT
11/19~74 ~ : E~ROR STATUS WORD
START STRING
~ ' START STRING
LINE CONFIG.
@ ~
OUTPUT LEYEL
J
GENERATE
END STRING
LINE CONFIG.
OUTPUT LEVEI
J
OE NERATE
' END STRING
END I/O
~ END I/O
STA~T I/O
~DDRESS
~ ADD~ESS
STA~T STRING
~ START STRING
LINE CONFIG.
DELAY
. D
ADJUST A~C
SAMPLE
END STRING :
~16 10~4Z58 A N~R P02 COMPUTER GENERATOR LOCAL UNIT
CH~/ck 11/19 / 74 ~ LINE CONFIG .
+ DELl~Y
D
ADJUST AGC
SA~LE
t END STRING
END I/O ~
~ END I/O
: START I/O ~
ADD~ESS ~ -ADDRESS
SEND SA~!lPLES
~ SEND SAMPIES
MODEM
MODEM
AGC SETTING
t CHECKSUM PARITY
END I / O
END l/O
EE~gOR STATUS: ~ORD
BIT 1 = CHECKSUM PARITY ~RROR
BIT 2 = TR~ISMISSION ERROR
BIT 3 = TOO FEW CHAE~ACTERS
B~CT 4 = TOO MANY CHARACTERS
BIT 5 = l : BIT 6 - 1 ` 30 BIT 7 = 0 BIT 8 = ODD PARITY
It is evident that those skilled in the art may enter a sequence of these steps in a program register so that testing of a line may be rapidly initiated by identifying the local units and specifying the tests to be made.
The above description of a specific embodiment is by A NOR P02 way of example for illustrating the best mode now CH/ck 11/22/74 contemplated for practicing the invention and is sufficient to enable anyone having ordinary skill in the art to practice it.
The invention has a number of features. The concept of having one or more local programmable units communicating with a central digital computer affords great flexibility in testing ~OS42S8 A NOR P02 at relatively low system cost reliably over relatively inexpensive CH/ck 11j2~/74 communication channeIs to rapidly effect a wide'number of tests.
The Iocal unit includes a digital input/output for communicating with'a digital computer and an analog input/output for communica-tion with'a line under test, To this end it includes a shift reg-ister waveform generator that may receive a sequence of multi-bit digital numbers representative of a waveform serially at a rela-~ tiveIy slow rate and provide these digital number signals in se-; quence in paralleI form to a digital~to-analog converter to produce the'desired test analog signal as the shift register is shifted at a much'faster rate than the rate at which waveform data may enter, A similar unit may be used for accepting a digital representation of a received signal waveform and delivering it at a slowèr rate for transmission to the central office digital ~ computer.
'~ Still another feature of the specific embodiment resides in controlling the'input signal leveI so as to maximize the digital reso-lution of the received input signal, Still another feature of the învention is the ability of each l'ocal unit to function as either or both of transmitters and receivers, Still another feature of the invention is the use of ~ immediate'c'ommands and string commands, By sending the immediate ; ' command twice, each l'ocal unit is almost certain of having re-ceived the correct command because'the failure to indicate a compare of successive'immediate commands may be used to prevent execution of the immediate command and cause transmission of an error signal to the central computer, By transmitting back'to the central computer every' command, the central computer may be'programmed to prohibit execution of string commands unless the received string commands compare with'the'transmitted string commands.
The waveform designations may be sent once while using conventional error checking techniques. ' A NOR P02 It is apparent that those skilled in the art may now OE/ck 11`/22/74 make numerous uses and modifications of and departures from the specific em~odiments and techniques herein disclosed without departing from the principles of the invention. Consequently, the invention is to be'construed as embracing each and every novel feature and noveI c'ombination of features present in or possessed '~ by the'apparatus and techniques herein disclosed and limited soleIy by the spirit and scope of the appended claims.
What is claimed is:
. ~
~20~
CH/ ck lljl9/74 The present invention reIates' in general ~o program~
mable me~suxing and more particularly concerns noveI apparatus and techniques for rapidly and automatically testing the trans-mission characteristics of a communications channel that may be remote from a central computer through measuring analog test sîgnals transmitted over the channel while communications between the central computer and the'terminal points of the channel under test are'through reIiable digital signals to enable the digital computer to readily determine'the transmission characteristics of the communications channel under testO
~ A typical prior art approach to checking a communications j channeI: comprises a local computer in a closed loop including the communications channel to be tested. Having a digital computer for each communications link is costly, for a typical communica-, tions system has many linksO
Accordingly, it is an important object of this invention to pro~îde apparatus and techniques that facilitates' using one digital computer to automatically'measure transmission charac-terist:ics of a number of communication links in a commun:ications systemO
It is a further object of the invention to achieve`one or more of the preceding objects with'programmable local units that are reIatively inexpensive and reliable.
It is a further object of the invention to achieve one or more'of the preceding objects with'programmable local units characterized by a high degree of flexibility and capable o functioning both to receive and transmit test signal waveforms and to accept digital command signals from the computer and provide digital signals to the computer relevant to the'programmable measurements being madeO
It is a further object of the invention to provide novel ~2~
A ~OR P02 apparatus-and techniques,for providing a wide variety of waveforms.
/74 It is a further ob~ect of the invention to provide a programmable local unit having both a digital signal input and a digital signal output for communication with a digital computer and an analog input and analog output for exchanging signals with a communication link to be testedO
It is still a further object of the invention to provide noveI shift regist-er techniques for generating analog waveformsO
It is still a further object of the invention to provide sh~ft register techniques,for converting a received analog signal into corresponding digital signals.
It is still a further object of the'invention to achieve one or more o the preceding objects while'controlling signal gain to keep signal levels so as to obtain substantially maximum resolution.
SUMMARY OF THE INVENTION
',~ According to the'invention, there is a central digital computer that transmits digital signals to a programmabIe local , unit at an end of a communication channel to be'tes.ted. A
programmable'local unit includes means responsive'to the.'digital ' signal, from the digital: c'omputer for providing an analog signal `:
~ waveform for transmission over the communieation channel under : test and means responsive'to the received test analog signal transmitted oYer the`commun:ications link for converting the ,~ recei.ved signal into a rep.resentative digital signal that is transmitted to the digital computer to enable the'latter to determ,ine'the transmission characteristics of the communications link'under test.
A local unit according to the invention includes gener-ator buffer means o~ storing a sequence of digital numbers : representative of a signal waveform to be transmitted over the communicationslink to be'tested, digital-to-analog converting means -3~
105~Z58 A NOR P02 coupled to the generator buffer'means for converting the digital /74 signal provided by the generator buffer means into a corresponding analog signal and output level control means for controlling the amplitude'of the latter analog signal to a predetermined level for transmission over the communications link to be tested that is deIivered to line interface means for exchanging signals with the local unit and the communications link.under test. The local unit also includes input level control means for .controlling the amplitude of a signal provided by the'communications link under test to a predetermined level, analog-to-digital converting means responsive to the latter signal of controlled le~el for providing a representative digital signal, and receiving buffer means for storing the latter digital signals as a sequence of digital numbers representatîve of the signal received over the communications link for transmission to the'remote'computerO The local unit also in-cludes microprocessor control means for controlling the leveIs, the'conversions between analog and digital form and receiving ap~
propriate instructions from the remote computer to load a desired signal waveform into the'generator buffer means and to unload a digital representation of the received waveform from the receiving buffer'means for tra,nsmission back to the remote computerO
A,feature'of the local unit is that it has means for exchanging digital signals representative of analog signal wave-forms transmitted over a communications link under test and means for exchànging these analog signal waveforms with the comm~nications lînk under test, A more specific feature of the invention is the.form of the generator and receiving buffer means. Each t~pically comprises a plurality of shift registers that exchange'digital number signals representative of analog signal waveforms in paralleI at one end and exchange digital number signals serially representative of an analog signal waveform at the other end.
lOS4ZSB
A NOR P02 Still another feature of the invention is the.'use of CH/ck :11/-1~/74 digital automatic gain control'means..~or adjusting. the input level to obtain maximum reso.lution of the analog signal with'the available bits for digital conversion, the means inc.luding a swîtched gain amplifier with negligible phase shift.
Numerous other fea.tures, objects and advantages of the înventîon will become'apparent from the following specification when read in connectIon with the'accompanying drawing in whîch:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram illustrating the logical arrangement of a system according to the invention; and FIG. 2.is a block diagram îllustrating the logîcal arrangement of a local unit according to the invention, DET~ILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference'now to the'drawing and more particularly FIG. 1 thereof, there îs shown a block diagram illustrating the : log.ical arrangement of a system according to the'inventionO A
central office 11 inc.ludes a central computer, such as a Digital A~. (T~) memory ' ~' Equipment Corporation PDP-8Elhavîng a 16K bit core/and disc memory coupled.to a conventional teIetypewriter 13 for accepting informa-tion on tests to be made'and printing out the'results.of the test.
Central computer 12 is coupled to teIephone lînes through line interface 14, such as BeIl 2Q2. data sets. TeIephone lines 15 and 16 intercouple'central office line interface 14.wîth local units 17 and 18, respectîveIy, inte.r.coupled by line 21.under test.
In the exa,m,ple'.local unît 17 is indicated as functioning as a generator that transmits analog waveform 22.over line 21 to local unit 18 functioning as a receiving unit for the'analog waveform 22. However, it is within the principles of the inven-tion for each'local unit to function as one'or both of transmitting and receîving-unitsO For examp:le, it is within the principles of the invention to transmit the analog waveform 22:f~om remote ~5~
A NOR P02 site number 1 to remote site number 2 and back to remote site /74 number 1 ~ith local unit 17 functioning as bo.th. transmitter and receiver so that line 21 could be tested with but a single communi-cation link between central office 11 and remote site number 1.
Having discussed the physical arrangement of a system according to the invention, its mode of operation will now be discussed. An operator enters on teletype 13 information on the test to be performed, the line to be tested and the local unit or units to be used in the tests. The test to be performed may be those useful in checking a particular communications link.
For example, typical measurements made on a teIephone line include single tone interference loss, frequency shift, phase jitter,/and C-notched noise using a 1015.625Hz taneO Other measurements typically made include those of second and third intermodulation distortions using the sum of three tones, attenuation and delay distortions using a spectrum filling signal and C-message noise using a quiet termina-tionO The specific tests are not a part of the invention and are by way of example in connection with illustrating the best mode now contemplated for practicing the inventionO
Typically, the test might be a frequency response tes~
: to de.termine attenuation distortion and deIay distortion at specified impedance levels, typically 600 ohms. With local unit 17 identified as the generator and local unit 18 identified as the receiving unit, each receives digital signals over lines 15 and 16, respectiveIy, that readies each to perform its desired function. Thus, local unit 17 proceeds to transmit a spectrum of tones o~er line 21 that is received by local unit 18 which then transmits a digital representation o~ the signal waveform over line 16 to central computer 12:through interface 14 so that central 30 computer 12 may process the. digital representation ~nd print out on teIetype 13 test results, typically listing each frequency of the transmitted spectr~m followed by the attenuation at that ~6~
1054Z58 `
A NOR P02 frequency and the deIay at that frequency. The'specific techniques, /74 such'as fast ~ourier tr~nsform methods, for processing digital representations of measurements received at different frequencies to print out a frequency response are well-known in the digital computer art, are not a part of the invention and are not described in detail herein so as to avoid obscuring the'principles-of the invention.
In a typical requency response measurement the local unit transmits digital samples of the received waveform to the central computer representative of a voltage'waveform as a function of time in the time'domain similar to what would be observed using an oscilloscope, The central computer uses a Fast Fourier Transform algorithm to convert the samples to amplitude and phase as a function of frequency in the ~requency domain to represent the'received waveform by its spectral components, The computer subtracts the'received amplitude from the'transmitted amplitude'at each frequency to determine attenua-tion and takes the derivative'of the phase'response'with'respect to frequency to determine'deIay. These methods are'weIl-known in the digital signal analysis field~
- Referring to FIGo 2 ~ there is shown a block diagram illustrating the'logical arrangement of an exemplary embodiment of a local unit according to the invention. The local unit includes a 1200 baud half duplex modem 23 for interfacing with the teIephone lines to the central office, such'as 15 or 16, for exchanging digital data signals therewith'at a 1200 baud rate. A micro-process-or control means 24 exchanges digital data with modem 23 and signals with the other eIements of the local unitO The local unit includes a generator buffer 25 for receiving a sequence of digital numbers representative'of a waveform to be tran'smitted oyer test line 21~ a digital-to-analog converter 26 for converting the sequence of digital numbers provided by generator buffer 25 -7~
~05~258;
A NOR P02 and an output filter,output level controller 27 for controlling ~/74 the level of the analog signal for transmission over test line 21 and a line interface 30 for coupling the tes't signal from out-put leveI controller 27 to line 21 and coupling ~ si~nal received from line 21 to input filter and input level controller 31 in the receiving branch of the local control unit. The receiving portion of the local unit also includes an analog-to-digital converter 32.for converting the received analog signal of controlled leveI into a sequence of digital number signals that are'entered parallelly in receiving buffer 33~ Receiving buffer.33 provides a sequence'of digital numbers to the central office through modem 23 under the control of microprocessor control means 24.
The local unit may also include a general purpose bus 34 for exchanging data with local apparatus at the location of the local control unit, such as a local computer, keyboard/display, digital.voltmeter, other instruments or RAM or ROM storage means.
Having briefly described the physical arrangement of the local unit, its mode of operation will now be discussed.
12QO baud half duplex modem 23 is capable of interfacing with any computer and receives commands and generator sequences from the computer for transmission over test line 21 while sending results of commands and samples in digital form of a test signal received - on test line 21 to the'central office computerO Preferably these digital signals are in ASCII code with'odd parity.
: Microprocessor control means 24, typically an Intel MCS-4 integrated circuit, accepts commands from modem 23 or general purpose bus 34 and decodes and executes these commands.
~ list of the commands are set forth below~ The specific means for decoding and executing commands are weIl-known in the art and not described in detail to avoid obscuring the'principles of the invention.
~8 A NOR P02 When the local unit is functioning in the'transmit mode, /:74 generator bufer 25, typ.ically capable of storing 512:12-bit digital ~ords, receives a sequence of 12-bit words through control means 24 and modem 23, the digital data entering in byte form.
Microprocessor control means 24 then causes generator buffer 25 to be cycled typically at an'8000 Hz rate to provide paralleI ac-cess to each'l2-bit digital number signal for conversion by digital-to-analog converter 26 into a representative amplitude level that is controlled by output level controller 27 under the control of microprocessor. control means 24 to provide on line 21 the test signal. ' ~ For testing typical telephone lines the filter portion : Of output le~el-controller ' and filter 27 is typically flat to.3000 Hz,.3dB down at 3200 Hz and 60dB down at 8000 Hz,. the . cycling rate.
Line interface 31 may include switching relays for ef-fecting appropriate'connections ta transmit terminal-2IA and re-ceive'terminal 2IB of line'21. For example,' the switching relays ~ay switch'in an appropriate'terminating impedance,' typically 600 ~ 2Q or ~00 ohms, a quiet termination for measuring quiescent noise or .~.'' effect a loop around wherein the'test signal is received on input with less or gain in level ~-~ 21B and retran'smitted on output 2LA/so that all communication with ~ the'central office compute-r may be'essentially with'one'local unit.
';. ~ A received signal thr~ugh line interface 31 is typically applied to input filter and level controller 3I, typically filtered, . ~ in accordance with'similar transmission characteristics. described above in connection with' outp.ut.level controller and filter 270 Level controller.31 typically amplifies the received input signal to a maximum of 60dB in 4dB increments to insure better than ll-b.it resolution~ This amplification is preferably accomplished automatically so that the maximum level provided at the'input to analog~to~digital: con~erter.32..corresponds to ~9_ ~0542S8 A NOR P02 the largest value of a 12~bit binary numberO This may rapidly ll`/L5/74 be accomplished automatically by initially setting. the`amplifica-tion at 60dB and decreasing the ampliication in steps untiI this maximum digital number value is provided by analog-to-digital con-verter 320 Analog-to-digital converter 32 converts the filtered input signal into 12-bit samples at an 8000 ~z rate that are stored in receiving buffer.33. Microprocess-or control means 24 then effects the transfer of the digital numbers stored in receiving buffer 33 in byte form through modem 23 to the central office computer~ Since the central office computer then has a digital representation of both the transmitted test signal and the corresponding received signal, well-known techniques may be : used to digitally evaluate transmission characteristics of the line, such as frequency response, distortion and noise leveI. The specific techniques for performing these evaluations digitally are well-known in the digital computer art, are not a part of this invention and are not described in detail here to avoid obscuring the principles of the invention, There follows a list of typical commands to the local unit-and responses from the local unit together with appropriate . designations on a conventional keyboard that may be used for desig-nating these commands, the nature of the command and whether it is an immediate or string command. The significance of the commands will then be described.
COMM~DS
Load Waveform 1 Two Character Immediate ~s~Second Character = From Where to Load .Assigned Wher~ s - M Modem R Receiver Buffer 0~15 ROM/R~M On GP Bu.s Send Samples 2. Two Character I~mediate Second Character = Where to Send Assigned Where s - M Modem T Transmitter Buffer 0-15 ROM/RAM on GP Bus lOS4Z58 A NOR P02 Start String 3 One Character Immediate CH/ck llllg!74 String Enable 4 One Character Immediate Retransmit 5 One Character Immediate Conditional End I/0 6 One Character Immedia~e Identify 7 One Character Immediate Stop Generator = One Character Immediate Self Test ~ One Character Immediate Bus Clear ? One Character Immediate Start I/0 CR Two Character Immediate Second Character = Local Unit Address End I/0 NAK(ERR) One Character Immediate ~bort BS (FE? One Character Immediate Set Output Level 0 Two Character String Second Character = Six Bit ASCII Word Giving Amount to Decrease Output From MAXIMUM.
(Most Significant Bit) MSB= ~32DB, -16DB, -8DB, -4DB, -2DB, -lDB = LSB (Least Significant Bit) Generate G Two Character String Second Character = Six Bit ASCII Word Giving Number of Sample Periods as Length of Generate Time -@ = Generate IndefiniteIy Adjust AGC A One Character String Set Input Gain I Two Character String Second Character = Six Bit ASCII Word Giving Input Gain MSB = ~3~DB, +16DB, +8DB, +4DB, X, X = LSB
Sam~le S One Character String Line:Configuration L Two Character String Second Character = Six Bit ASCII Giving New Line Configuration MSB= Input ReIay, Bridge, Loop? 600~9.00SZ, Output Relay, Modem = LSB
Delay D Two Character String Second Character = Six Bit ASCII Giving Number of Sample Periods to DeIay @ = ~o Delay End String E One Character String Interxupt M Two Character String Second Character - Data For GP Bus With IRT
Acti~e Universal Bus Command U Two Character String Second Character = Least Significant Five Bits Are Unlversal Bus Command -~os4~ss A NOR P02 Begin Bus Data B One Character String /74 Finish Bus Data ~ One Character String The commands are classified as immediate and string.
An immediate com~and is one that is executed immediately upon receipt by the local unit. String commands are stored in random access memory comprising'microprocessor control means 24 and executed sequentially after the End I/O command~
We turn now to a discussion of the specific commands.
The LOAD ~AYEFORM command is typically designated by pressing the 1 key followed by a second character designating from where'to load. Thus, pressing M selects the modem as the source of a digital representation of the test waveform for storage in generator buffer 25, pressing R selects receiver buffer 33 as the source'and pressing numbered keys from 0-15 select specific ones of waveforms that may be locally stored in a random access memory or read only memory at the location of the local unit through general purpose bus 34.
The'SEND SAMPLES command is selected by pressing 2 fol-lowed by a character designating where to send the samples, M for the''modem, T for the generator buffer 25 and 0-15 for a designated one'of random access or read only memories through general purpose bus 34.
Pressing 3 designates the START STRING COMMAND to cause the'local unit to store'the following commands as string commandsO
Pressing 4 selects the'STRING ENABLE command to condition the local unit to enable a previously stored string.
Pressing 5 causes the'local unit to retransmit its last response'to the computer, Pressing 6 implements CONDITIONAL END I/O whereby digital communic~tion stops and no string is executed, Pxessing 7 implements IDENTIFY for directing the local unit to command devices on the GP Bus to identify th~emselves.
1054Z58 f A NOR P02 Pressing = implements the STOP GENERATOR command for CH/ck 11/-19/74 ending the transmission of a test signalO
Pressing > implements~the SELF TEST command whereby the local unit may perform a self testing routine to insure proper operation.
Pressing ? impIements BUS CLEAR command to terminate the'data transmission on the GP bus, Pressing CR followed by a local unit address designation im~lements the START I/O command for establishing communication with the local unit to receive'appropriate commands~
Pressing NAK implements the END I/O comm~nd for ending this exchange and executing any enabled string.
Pressing BS implements the ABORT command which causes the local unit to abort the immediate command then being executed.
Pressing O followed by a second character that is a 6-bit ASCII word designating the amount to decrease the output from MAXIM~M by -32, ~16, ~8, ~4, ~2 and ~lDB from t~e most signi-fîcant ta the least significant bit, respectively, and effect the setting of output level controller 27 accordingly.
Pressing G followed by a 6-bit ASCII word giving the numbe~ of sample'periods as the length of the generation time effects the'GENERATE string command that causes the waveform stored in generator buffer 25 to be provided on test line 21 for the designated period, pressing @ following G causing the'waveform to be generated indefinitely until a stop generator command, Pressing A seIects the'A~C string command that causes the lcvel setting of leveI controller 31 to maximize'the'resolution as described above~ Pressing I followed by a second character in 6-bit ASCII im~lements the SET INPUT GAIN command that sets the'level of input level controller 31 to a level designated by the'ollowing ASCII word with the'sixth through third bits designating *32DB, ~16DB, ~8DB and ~4DB increments of gain, -~054258 Pressing S im~lements the SAMPLE string command which causes the'received signal to be'converted into digital form and stored in receiver buffer 33r Pressing L followed by a six-bit ASCII character imple-ments the'LlNE CONFIGURATION c'ommand to control the relays in line interface.3I to estabIish'the'various:connections and terminations described above.
Pressing D followed by a second character in:6-bit ASCII code'identifies a number of sam~le'periods to deIay before executing the next string command while'pressing @ produces no delay, : Pressing E implements the END STRING command, thereby signifying the end of a group of string commands and returning the'local unit to imm.ediate mode.' Pressing M followed by a second character addresses devi-ces 1 ~
/ o.n the general purpose'bus with'IRT activeO' .. Pressing U followed by a second character implements an:UNIVERSAL BUS COMWAND for the'general purpose bus.34. Pressing B im~lements- the BEGIN BUS DATA as a one character string to cause : ~20 the following data in the string to be'applied to the general: purpose'bus.34, and pressing a implements the'FINISH BUS DATA
command that is a one'character string for terminating the transfer of the data oYer the'general purpose'bus.34.
The'local unit may also transmit replies which'may be observed on the'teletype at thé central stationO Observation of ~ indicates a transmission ~error, such'as a parity error, an overrun or framing errorO Obs'ervation of >> indicates a mode`
' error whereby a string command was received in the'immediate`mode.
Obsexvation of # signifies an illegal command, such as an unassigned.command, uneq.ual characters or loss of carrierO ' Observation of $.indicates that the'assigned command is done, such'as sampling or self-test. 'Obse.rvat.ion % indicates fail, such : -14-~054Z58 as the'sampler.ove.rloaded or the seIf-test failed.
Observation of & signifies service .re~ue.st, indicating that the`general purpose'bus needs ser~ice.
Each local unit has a~unique address which'allows more than one'unit to share a single l2QO baud line'to the central computer 12. A START I/O comm~nd signal followed by an address : signal initiates a command sequence'to the'local unit addressed.The addressed local unit executes immediate'commands immediately upon receipt without transmission errors. The string commands are : 10 stored in xandom access memory.comprising microprocessor: control m.eans 24 and executed after receipt of an END I/O command signal.
:'~ Either an END I/O or CONDITIONAL END I/O command signal must te'rminate'a command sequence'before a different local unit may : be'addressed, the latter: command signal not causing exe~ution of string. commands. Each local unit is in the'immediate''mode at the r beginning of a command sequence The'START STRING command signal alerts the addressed local unit that string commands follow.
The EN.D STRING command signal returns the.'unit to the'immediate de.
20 There is set forth'beIow a typical immediate'command format indicating the exchanges between the central computer and the Iocal unit.
CQNPUTER GENERAT'O.R LO.~AL'UNIT
START I~O
ADDRESS
~ : ADDRESS
LOAD WAYEFOg~ -+ LOAD WAYEFORM
MQDEM
+ ~ODEM
512 12~BIT WORDS
CHECKSUM PARITY.
~15-~05~258 k COMPUTER GENERATOR LOCAL UNIT
11/19~74 ~ : E~ROR STATUS WORD
START STRING
~ ' START STRING
LINE CONFIG.
@ ~
OUTPUT LEYEL
J
GENERATE
END STRING
LINE CONFIG.
OUTPUT LEVEI
J
OE NERATE
' END STRING
END I/O
~ END I/O
STA~T I/O
~DDRESS
~ ADD~ESS
STA~T STRING
~ START STRING
LINE CONFIG.
DELAY
. D
ADJUST A~C
SAMPLE
END STRING :
~16 10~4Z58 A N~R P02 COMPUTER GENERATOR LOCAL UNIT
CH~/ck 11/19 / 74 ~ LINE CONFIG .
+ DELl~Y
D
ADJUST AGC
SA~LE
t END STRING
END I/O ~
~ END I/O
: START I/O ~
ADD~ESS ~ -ADDRESS
SEND SA~!lPLES
~ SEND SAMPIES
MODEM
MODEM
AGC SETTING
t CHECKSUM PARITY
END I / O
END l/O
EE~gOR STATUS: ~ORD
BIT 1 = CHECKSUM PARITY ~RROR
BIT 2 = TR~ISMISSION ERROR
BIT 3 = TOO FEW CHAE~ACTERS
B~CT 4 = TOO MANY CHARACTERS
BIT 5 = l : BIT 6 - 1 ` 30 BIT 7 = 0 BIT 8 = ODD PARITY
It is evident that those skilled in the art may enter a sequence of these steps in a program register so that testing of a line may be rapidly initiated by identifying the local units and specifying the tests to be made.
The above description of a specific embodiment is by A NOR P02 way of example for illustrating the best mode now CH/ck 11/22/74 contemplated for practicing the invention and is sufficient to enable anyone having ordinary skill in the art to practice it.
The invention has a number of features. The concept of having one or more local programmable units communicating with a central digital computer affords great flexibility in testing ~OS42S8 A NOR P02 at relatively low system cost reliably over relatively inexpensive CH/ck 11j2~/74 communication channeIs to rapidly effect a wide'number of tests.
The Iocal unit includes a digital input/output for communicating with'a digital computer and an analog input/output for communica-tion with'a line under test, To this end it includes a shift reg-ister waveform generator that may receive a sequence of multi-bit digital numbers representative of a waveform serially at a rela-~ tiveIy slow rate and provide these digital number signals in se-; quence in paralleI form to a digital~to-analog converter to produce the'desired test analog signal as the shift register is shifted at a much'faster rate than the rate at which waveform data may enter, A similar unit may be used for accepting a digital representation of a received signal waveform and delivering it at a slowèr rate for transmission to the central office digital ~ computer.
'~ Still another feature of the specific embodiment resides in controlling the'input signal leveI so as to maximize the digital reso-lution of the received input signal, Still another feature of the învention is the ability of each l'ocal unit to function as either or both of transmitters and receivers, Still another feature of the invention is the use of ~ immediate'c'ommands and string commands, By sending the immediate ; ' command twice, each l'ocal unit is almost certain of having re-ceived the correct command because'the failure to indicate a compare of successive'immediate commands may be used to prevent execution of the immediate command and cause transmission of an error signal to the central computer, By transmitting back'to the central computer every' command, the central computer may be'programmed to prohibit execution of string commands unless the received string commands compare with'the'transmitted string commands.
The waveform designations may be sent once while using conventional error checking techniques. ' A NOR P02 It is apparent that those skilled in the art may now OE/ck 11`/22/74 make numerous uses and modifications of and departures from the specific em~odiments and techniques herein disclosed without departing from the principles of the invention. Consequently, the invention is to be'construed as embracing each and every novel feature and noveI c'ombination of features present in or possessed '~ by the'apparatus and techniques herein disclosed and limited soleIy by the spirit and scope of the appended claims.
What is claimed is:
. ~
~20~
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for measuring characteristics of a communication channel between two terminals characterized by a programmable local unit at one of said two terminals for exchanging analog test signals with said communication channel, central digital computing means for exchanging digital information signals with said programmable local unit, and a first communications link between said central digital computing means and said local unit for relaying said digital information signals, said programmable local unit includes:
(a) a micro-processor accessible to said central digital computing means for storing a test sequence and associated instructions therein for delayed execution of said test sequence; and (b) means responsive to a received analog test signal transmitted over said communication channel for converting the received analog test signal to a representative digital signal for transmission to said digital computing means, whereby said digital computing means determines characteristics of said communication channel.
(a) a micro-processor accessible to said central digital computing means for storing a test sequence and associated instructions therein for delayed execution of said test sequence; and (b) means responsive to a received analog test signal transmitted over said communication channel for converting the received analog test signal to a representative digital signal for transmission to said digital computing means, whereby said digital computing means determines characteristics of said communication channel.
2. Apparatus for measuring characteristics of a communication channel in accordance with claim 1 and further comprising:
a second said programmable local unit at the other of said two terminals, and means defining a second communications link between said central digital computing means and said second programmable local unit for exchanging digital signals therebetween, one of said programmable local units being for receiving command signals from said digital computing means to generate an analog test signal for transmission over said communication channel to the other of said local programmable units, said other local programmable unit being for receiving digital command signals from said digital computing means and for transmitting digital signals to said digital computing means representative of the received test analog signal after transmission over said communication channel.
a second said programmable local unit at the other of said two terminals, and means defining a second communications link between said central digital computing means and said second programmable local unit for exchanging digital signals therebetween, one of said programmable local units being for receiving command signals from said digital computing means to generate an analog test signal for transmission over said communication channel to the other of said local programmable units, said other local programmable unit being for receiving digital command signals from said digital computing means and for transmitting digital signals to said digital computing means representative of the received test analog signal after transmission over said communication channel.
3. Apparatus for measuring characteristics of a communication channel in accordance with claim 1 wherein said local programmable unit includes means for controlling the level of said analog signal waveform for transmission over said communication channel.
4. Apparatus for measuring characteristics of a communication channel in accordance with claim 1 wherein said local programmable unit includes means for controlling the level of said received analog signal.
5. Apparatus for measuring characteristics of a communication channel in accordance with claim 1 wherein said analog test signals are provided by buffer means for storing a sequence of digital byte signals representative of said analog signal waveform at a first rate, digital-to-analog converting means, and means for providing the digital byte signals stored in said buffer means at a second rate to said digital-to-analog converting means to provide the latter analog signal waveform.
6. Apparatus for measuring characteristics of a communication channel in accordance with claim 1 wherein said means for converting said received test analog signal comprises:
analog-to-digital converting means for providing a digital representation of said received test analog signal, buffer means responsive to the latter digital representation for storing a sequence of digital byte signals representative of said received analog signal waveform at a second rate, and means for transmitting the latter stored sequence of digital byte signals at a first rate different from said second rate to said digital computing means.
analog-to-digital converting means for providing a digital representation of said received test analog signal, buffer means responsive to the latter digital representation for storing a sequence of digital byte signals representative of said received analog signal waveform at a second rate, and means for transmitting the latter stored sequence of digital byte signals at a first rate different from said second rate to said digital computing means.
7. Apparatus for measuring the characteristics of a communication channel in accordance with claim 5 wherein said means for converting said received test analog signal comprises:
analog-to-digital converting means for providing a digital representation of said received test analog signal!
receiver buffer means responsive to the latter digital representation for storing a sequence of digital byte signals representative of said received analog signal waveform at said second rate, and means for transmitting the latter stored sequence of digital byte signals at said first rate to said digital computing means.
analog-to-digital converting means for providing a digital representation of said received test analog signal!
receiver buffer means responsive to the latter digital representation for storing a sequence of digital byte signals representative of said received analog signal waveform at said second rate, and means for transmitting the latter stored sequence of digital byte signals at said first rate to said digital computing means.
8. A programmable local unit for exchanging digital signals with a central computer and analog signals with a communication channel whose characteristics are to be measured comprising, means responsive to digital signals provided by said central computer for providing an analog signal waveform for transmission over said communication channel, and means responsive to the received test analog signal transmitted over said communication channel for converting the received analog signal into a representative digital signal for transmission to said digital computer.
9. A local programmable unit in accordance with claim 8 and further comprising means for controlling the level of said analog signal waveform for transmission over said communication channel.
10. A local programmable unit in accordance with claim 8 and further comprising means for controlling the level of said received analog signal.
11. A local programmable unit in accordance with claim 8 wherein said means for providing an analog signal waveform comprises generator buffer means for storing a sequence of digital byte signals representative of said analog signal waveform provided by said digital computer at a first rate, digital-to-analog converting means, and means for providing the digital byte signals stored in said generator buffer means at a second rate to said digital-to-analog converting means to provide the latter analog signal waveform, receiving analog-to-digital converting means for providing a digital representation of said received test analog signal, receiver buffer means responsive to the latter digital representation for storing a sequence of digital byte signals representative of said analog signal waveform at said second rate, and means for providing the latter stored sequence of digital byte signals at said first rate for transmission to said digital computer.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/532,746 US4001559A (en) | 1974-12-16 | 1974-12-16 | Programmable measuring |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1054258A true CA1054258A (en) | 1979-05-08 |
Family
ID=24122998
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA241,754A Expired CA1054258A (en) | 1974-12-16 | 1975-12-15 | Communication line test apparatus |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4001559A (en) |
| JP (1) | JPS5192641A (en) |
| BE (1) | BE836701A (en) |
| CA (1) | CA1054258A (en) |
| DE (1) | DE2556600A1 (en) |
| ES (1) | ES443520A1 (en) |
| FR (1) | FR2295651A1 (en) |
| IT (1) | IT1050777B (en) |
| NL (1) | NL7514443A (en) |
| SE (1) | SE7514222L (en) |
Families Citing this family (27)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4105995A (en) * | 1976-06-16 | 1978-08-08 | Hewlett-Packard Company | Digitally controlled transmission impairment measuring apparatus |
| US4112414A (en) * | 1977-01-03 | 1978-09-05 | Chevron Research Company | Host-controlled fault diagnosis in a data communication system |
| DE2723705C2 (en) * | 1977-05-26 | 1982-12-09 | Rohde & Schwarz GmbH & Co KG, 8000 München | Testing and monitoring device for high-frequency communication systems |
| DE2819776A1 (en) * | 1978-05-05 | 1979-11-15 | Teradyne Inc | Testing telephone lines to determine electrical characteristics - using LF test signal between two wires or between either wire and earth for fault detection and location |
| FR2430621A1 (en) * | 1978-07-03 | 1980-02-01 | Teradyne Inc | Testing telephone lines to determine electrical characteristics - using LF test signal between two wires or between either wire and earth for fault detection and location |
| US4273970A (en) * | 1979-12-28 | 1981-06-16 | Bell Telephone Laboratories, Incorporated | Intermodulation distortion test |
| US4301536A (en) * | 1979-12-28 | 1981-11-17 | Bell Telephone Laboratories, Incorporated | Multitone frequency response and envelope delay distortion tests |
| IT1128762B (en) * | 1980-02-20 | 1986-06-04 | Cselt Centro Studi Lab Telecom | CIRCUIT FOR DIAGNOSIS OF PCM CONNECTION NETWORKS |
| US4316259A (en) * | 1980-03-18 | 1982-02-16 | Grumman Aerospace Corporation | Programmable function generator |
| US4417337A (en) * | 1981-06-29 | 1983-11-22 | Bell Telephone Laboratories, Incorporated, | Adaptive multitone transmission parameter test arrangement |
| US4633411A (en) * | 1982-12-27 | 1986-12-30 | Rockwell International Corporation | Link quality analyzer |
| IT1192090B (en) * | 1985-06-20 | 1988-03-31 | Flitel Spa | AUTOMATIC FAULT LOCATOR ON TELEPHONE LINES |
| US4748625A (en) * | 1986-07-28 | 1988-05-31 | Motorola, Inc. | Optimum baud rate transmission system |
| EP0418282A4 (en) * | 1988-06-01 | 1993-04-07 | Standard Telephones And Cables Pty. Limited | Portable call generator |
| US4862492A (en) * | 1988-10-26 | 1989-08-29 | Dialogic Corporation | Measurement of transmission quality of a telephone channel |
| US5375159A (en) * | 1992-09-29 | 1994-12-20 | C & P Of Virginia | System and method for remote testing and protocol analysis of communication lines |
| GB9315353D0 (en) * | 1993-07-23 | 1993-09-08 | British Telecomm | Testing telecommunications equipment |
| US5521959A (en) * | 1994-02-09 | 1996-05-28 | Harris Corporation | Programmable source for supplying controllably variable AC/DC voltage output for telephone line measurement apparatus |
| US5504801A (en) * | 1994-02-09 | 1996-04-02 | Harris Corporation | User-controlled electronic modification of operating system firmware resident in remote measurement unit for testing and conditioning of subscriber line circuits |
| GB9411360D0 (en) * | 1994-06-07 | 1994-07-27 | Newbridge Networks Corp | Method of monitoring a network |
| US5995588A (en) * | 1995-09-01 | 1999-11-30 | Crick; Robert G. | Tone location device for locating faults in a paired line |
| US5748876A (en) * | 1995-12-29 | 1998-05-05 | Mci Communications Corporation | System and method for testing acoustic modems with semantically encoded waveforms |
| US6144721A (en) * | 1996-01-05 | 2000-11-07 | Communications Technology Corporation | Apparatus and method for line pair testing and fault diagnostics |
| US7076378B1 (en) * | 2002-11-13 | 2006-07-11 | Current Technologies, Llc | Device and method for providing power line characteristics and diagnostics |
| US7327781B2 (en) * | 2002-12-17 | 2008-02-05 | Invensys Systems, Inc. | Universal intelligent modem |
| US7460467B1 (en) | 2003-07-23 | 2008-12-02 | Current Technologies, Llc | Voice-over-IP network test device and method |
| CN114024882B (en) * | 2021-09-23 | 2023-07-14 | 深圳市共进电子股份有限公司 | Router performance test method, device, system and storage medium |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3496536A (en) * | 1966-05-02 | 1970-02-17 | Xerox Corp | Data link test apparatus |
| GB1259614A (en) * | 1968-11-22 | 1972-01-05 | ||
| US3842218A (en) * | 1972-07-10 | 1974-10-15 | Porta Systems Corp | Automated telephony testing and polling apparatus |
| US3787810A (en) * | 1972-11-02 | 1974-01-22 | Burroughs Corp | Test method for a programmable data communication terminal |
| US3819878A (en) * | 1972-12-18 | 1974-06-25 | Antekna Inc | Transmission test set for telephone circuit data communication systems |
| US3875500A (en) * | 1973-11-28 | 1975-04-01 | Nasa | Pseudo-noise test set for communication system evaluation |
-
1974
- 1974-12-16 US US05/532,746 patent/US4001559A/en not_active Expired - Lifetime
-
1975
- 1975-12-11 NL NL7514443A patent/NL7514443A/en not_active Application Discontinuation
- 1975-12-15 JP JP50148561A patent/JPS5192641A/ja active Pending
- 1975-12-15 CA CA241,754A patent/CA1054258A/en not_active Expired
- 1975-12-15 IT IT30296/75A patent/IT1050777B/en active
- 1975-12-16 SE SE7514222A patent/SE7514222L/en unknown
- 1975-12-16 DE DE19752556600 patent/DE2556600A1/en active Pending
- 1975-12-16 FR FR7538467A patent/FR2295651A1/en active Granted
- 1975-12-16 BE BE162796A patent/BE836701A/en unknown
- 1975-12-16 ES ES443520A patent/ES443520A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2295651B1 (en) | 1979-09-07 |
| FR2295651A1 (en) | 1976-07-16 |
| NL7514443A (en) | 1976-06-18 |
| BE836701A (en) | 1976-04-16 |
| SE7514222L (en) | 1976-06-17 |
| ES443520A1 (en) | 1978-03-16 |
| DE2556600A1 (en) | 1976-07-01 |
| JPS5192641A (en) | 1976-08-13 |
| US4001559A (en) | 1977-01-04 |
| IT1050777B (en) | 1981-03-20 |
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