CA2027813C - Method and apparatus for controlling a digital crossconnect system from a switching system - Google Patents

Abstract

METHOD AND APPARATUS FOR CONTROLLING A DIGITAL
CROSSCONNECT SYSTEM FROM A SWITCHING SYSTEM
Abstract This invention relates to apparatus and a method for controlling a Digital Access and Crossconnect System (DACS) from a connected toll switching system. All control messages from operations support systems (OSS) for making crossconnect changes in the DACS are first routed to the toll switch. The toll switch extracts information needed to update its database and sends a control message to the DACS. In addition, the toll switch responds to changes in traffic patterns, perhaps due to the loss of a transmission facility, to generate a crossconnect change message to the DACS to rearrange facilities for more optimum performance.
Advantageously, the OSSs for DACS control and switch control is combined and thetoll network is made more responsive to traffic pattern changes and to losses oftransmission facilities.

Description

.

METHOD AND APPARATUS FOR CONTROLL]NG A DIGITAL `
CROSSCO~NECT SYSTEM FROM A SWITCHING SYSTEM[
;$ Technical Field ;
This invention relates to a method and apparat-ls for controlling a 5 crossconnect system from a switching system.
9 Problem A large common carrier network such as the AT'&T toll network, actually comprises two separate networks. The first is the switched network for `~ setting up individual connections in response to dialed individual customer requests, -.~
10 hereinafter referred to as the switched public common carrier network. The second ; ' ~.
is a facilities network for assembling small facility inputs such as a 1.5 megabit T~
;j carrier facility (DSl signal) into large facility outputs, for example for fiber optic transmission, for disass~mbling large facility inputs to generate small facilityoutputs, and for switching small facility outputs to destination outputs for use by the 15 switched public common carrier network and for use by private network customers.
The facilities switched network is colmected directly to the switched public common - - ~ ~-carrier network for providing facilities for carrying communications for the trunks used by the switched public common carrier network and is connected directly to ~-private network customers for providing private facilities to these customers.
~'~ 20 Although these two networks are heavily interconnected, they are administered separately. The facilities switching network comprises a plurality of ~' facilities crossconnect systems such as the Digital Access and Crossconnect Systems - (DACS); the crossconnect systems are an automation of manually controlled cross connect arrangements, interconnected with each other, with toll switches and with ~ :
25 private customers. The DACS systems differ in basic ways from toll or local switching systems. Unlike the toll or local switching systems which are alranged to switch between individual trunks, each for carrying one communication, the DACS ;
systems swiech facilities such as a DS1 signal for carrying communications of a plurality of trunks. The DACS switches operate relatively slowly for setting up long 30 term inter-switch connections and have no arrangements for responding to call .
' processing input signals from customers or from a switching system for setting up ., individual call connections. These switches are controlled by an operation support :~ system (OSS) which provides the basic information needed by DACS to set up the :
long term connections within each DACS system. This is in contrast to a toll 35 switching system, or toll switch, which responds to individual call set-up requests to set up one call connection, involving one trunk, at a time. Groups of trunks are then i's, $~ ' ' ;.
`' ,, ~ . .

.. ~ ..
attached on a non-switched basis to the facilities for carrying the communications on ~, these trunks.
The primary input for controlling switching in a toll switch is ~he signals, received directly or indirectly from an individual telephone customer, requ~sting a connection. In addition, an operation support systems for the to}l switches coordinates -;~ the translation data describing the destination of each trunk in a toll switch with the :~ actual destinations of these trunks as established by the DACS systems interconnecting the facilities that are carrying that trunk. Thus, the DACS systems use a completely ~`, separate information source for controlling the connection o~ the facility or facilities to be supplied for each route in the toll network.
; A problem in the prior art is that the DACS systems, which provide facilities to the toll switches, do not have information about the current status of traffic ~, in the toll network, thus making it impossible for these systems to respond directly to -' changes in traffic. Correspondingly, because of the separate engineering from di~ferent OSSs, only the DACS systems have access to the information about the use of facilities for private networks to indicate limitations of facilities which could be supplied to the public switched network. - -? A further problem is that many private network customers use private services provided directly through interconnected DACS systems and also use public ~ :-Z 20 services, such as sofh~vare defined networks, which are implemented through the use of the switched public common carrier network. The coordination of the response to customer demands .~or both of these services is difficult because of the separation of ,' administration of the DACS network and the switched public common carrier network.
In summary, problems of the prior art are that it is costly to have separate ~ i ;
~i~ 25 administration of the digital access cross connect network and the switched public -~
i, common carrier network, that this separate administration leads to an inefficient 5, interface with customers who have facilities terminating on both of these networks, and ~iJ that this separate administration makes it difficult to optimize the use of the totality of ,I capabilities of both networks.
'~ 30 Summan~ of the Invention c ~;
In accordance with one aspect of the invention there is provided in -combination, a switching system for selectively interconnecting ones of a plurality of communication circuits, interconnecL means ~or selectively interconnecting ones of a ~ .
~,~

.. :: - .

2 0 2 7 ~3 1 3 .
~ 3 : .
, .. ..
.-. ~- .
`; plurality of communication circuit multiplexes, said pluralits~ of multiplcxes comprising a i. first multiplex connected to said switching system, and control means, common to said .~ switching system and said interconnect means, for controlling both the interconnection by said interconnect means of ones oE said plurality of multiplexes, and the establishment by said switching system of calls to and from individual ones of said circuits of said first multiplex.
Brief Description of the Drawin~
FIG. 1 is a diagram of the prior art configuration between operation j~ supports systems (OSSs), DACS, and toll switches;
FIG. 2 illustrates the configuration in accordance with the principles of ~ ', this invention; . - .
:;' FIG. 3 is a block diagram showing interconnections among DACS, toll and ~, local switches, and customers;
FIG. 4 is a diagram of a toll switch;
:~15 FIG. S is a diagram showing inputs to a DACS;
` ~ FIG. 6 is a memory layout of memory in a toll switch for implementing the 3 invention;
~:~ FIG. 7 is a flow diagram of a program for a toll switch for implementing the invention;
FIGS. 8-10 are diagrams of a prior art switching system;
. 1 FIGS. 11a and 11b, arranged in accordance with FIG. 11, comprise a ~ .
diagram illustrating modifications and additions to the switching system of FIGS. 8-10 to provide the integration of an interconnection arrangement (a DACS) with a i`~ switching system, under a common control structure, in a central o~fice wire center :
CO-2000; and ~ -:~ FIG. 12 is a diagram of an add/drop filter ring architecture where the !! interconnection arrangement is implemented using add/drop multiplexers connected in ... a fiber ring in a distributed architecture rather than using a DACS. -,~ Solution ,, 3û A technical advance is made over the prior art in accordance with the : .
~i1 present invention wherein, in one exemplary es7lbodiment, the toll switches and the iY DACS are supplied with a control interface for permitting a toll switch to request facilities connections in the DACS switch. A toll switch, upon receipt or detection of ~ -information for setting up new trunk groups or adding or substrating from existing .
.
-:
:

2027~13 :::

- 4 ~
trunk groups sends control messages to the DACS to connect the facilities corresponding to these groups. The toll switch maintains a record of both private and public connections in the DACS in order to maintain the information necessary for de~e~nining whether and which additional facilities are available. The toll switch ~ ~ -S also receives direct custorner input for rearranging facilides for that customer.
Advantageously, since the toll switch network has direct acce ss to the present status ~ -`~ of public switched common carrier traffic, such arrangements make it possible to respond dynarnically to changes in these traffic patterns. Ad~rantageously, a single interface to an operation support system (OSS) can be used for controlling both the 10 toll switch and the DACS. Advantageously, customer signals received at the toll switch can be used to control DACS connections.
In accordance with one aspect of the invention, a DACS is controlled from an associated toll switch. Advantageously, such an arrangement permits maintenance control of the DACS from the toll switch and from the operation 15 support system associated with the toll switch.
~, Accordingly, this invention relates to a rnethod and apparatus for controlling an automatic facilities crossconnect system from a communications ~ -! switching system for generating and transmitting control messages to the - ~-crossconnect system for establishing and disconnecting crossconnections therein.20 An illustrative method of the invention is used in a central of fice wire center CO- -2000(FIGS. 11aand 1lb)includinganinterconnecta~angementa)NU2059) 3 ter~unating transrnission facilities (2060, 2070), and fur~her including a switching system including peripheral units (AIUs, TIUs) for interfacing peIiphe~al circuits (lines, trunks) with the switching system. The switching system also includes 25 switching units ~SIUs 2031, 2032,~ for providing switched communication amongthe peripheral circuits in response to calls to and from the peripheral circuits. The A wire centeT further includes a control means (AM 2052~ common to the intOEconnect , arrangement and the switching system. In response to the control means, the -i, intOEconnect a~angement interconnects the s~itching system and at least one 30 multiplex of circu~ts (e.g., a DS 1 multiplex comprising 24 circui~s) of at least one of - -the transmission facilities. Also in response to the control means, the switching system establishes calls to and from individual circuits of that multiplex.
The interconnect aIrangement also interconnects units of the switcAhing system. For example, the interconnect a~angement in~ercoMects a peripheral unit 35 (AIU 2117) at a remote terminal (RT-2000) and a switching unit (TSIU 2031) at the A central office wire center. Alternatively, the interCOMeCt alTangement interconnects s ~:

.~, ..... ., ,, :
"
, . . : :

.'t^.r . ~

:'f ~

2027813 ~
``~ 5 . ... ~
a peripheral unit and a switching unit that are both located at the central of fice wire - center. The interconnect arrangement is usable to interconnect two switching units, e.g., a host switching unit (TSIU 2031) at the central of fice w~ire center and a remote ~i switching unit (TSIU 2033) at a distance from the w~re center, or two distributed S switch units (TSrUs 2031, 2032) at the wire center. The switching system further includes a central sw~itch tCM 2055) for providing switched communication between different switching units (TSIUs 2031, 2032).
; An illustrative combination in accordance with the invention comprises a switching system, an interconnect means (DNU 2059), and control means 10 (AM 2052) common to the switching system and the intercormect means. The switching system selectively interconnects ones of a plurality of communication circuits (DS0 circults). The interconnect means selectively interconnects ones of a plurality of cornrnunicadon multiplexes (e.g., DS1 multiplexes each comprising 24 ~7 DS0 circuits). A first of the multiplexes (a DS1 on P~T link 2071) is connected to 15 the switching system. The control means controls both the interconnection by the -' interconnect means of ones of the multiplexes, and the establishment by the ~ ~ ~
switching system of calls to and from individual ones of the circuits of the first ~ ~;
multiplex. `
1 The control means includes a common operations, administration, ;~ 20 maintenance, and provisioning system for the switching system and the interconnect means. The interconnect means has a plurality of ports (connected to IUs 2063 2069) and intercormect control means (DACS controller 2061) for controlling the interconnection of the ports. The interconnect means and the switching system are colocated at a central office wire center (C0-2000). ; ~ -, 25 A second multiplex (a DS1 on link 2122) conveys information to and from peripheral communication circuits (lines 211g). The control means controls the interconnection by the interconnect means of the first and second multiplexes, and the establishment by the switching system of calls to and from individual ones of the peripheral circuits via the first muldplex, the interconnect means, and the second -30 multiplex. -A third multiplex (a DS 1 on link 2060) and a fourth multiplex (a DS l on link 2070) are not connected to the switching system. The control means controlsthe intercoMection of the third and fourth mul~plexes. The third and fourth muItiplexes may be connected to o~er switching systems and intercoMect means 35 that are independent of the control means.

- 5a -~-In an alternative embodiment ~FIG. 12), the function of the interconnect arrangement, rather than being performed by a cross connect system, is instead performed by a plurality of add/drop multiplexer units (DDh/1-2000) each connected to an associated distributed switch means (SM-2000) and controlled by the associated distributed control means (SMP). The multiplexer units are interconnected in a fiber ring.
~ Detailed I)escription 3 FIG. 1 depicts the prior art. Two separate operation support systems . (OSSs) exist, one, a DACS administration system 401 and the other a toll :~ 10 administration system 405. The DACS administration system is aware of facilities .
that are connected to the DACS 403. The DACS administration system sends control messages over link 411 to request the DACS 403 to set up connections for . ^~
facilities 413 between interconnecting the DACS 403 and toll switch 407. These ::
3 requests include requests to set up a facility connection between some large ' ~`'''`'~
~ :

' .. ~ ':

~ 13 2 i ~ L ~ ~ -. . :.:
customer and a toll switch for providing access by that customer to the public switched network or to a switched private network; to set uFI facilities connecdons !~ between two cus~omer locations; to set up facilities connections between a customer location and another DACS for further connection to another customer location, 5 another DACS or another toll switch; to set up facilities connections between an input of a DACS and an output of a DACS for providing a connection for a facility .` passing through the DACS; to set up facilities connections between an incoming -~ facility and the toll switch for providing switched connections for the public switched network; and to set up facilities connections between facilities to a local 10 switch and facilities to a toll switch. The administration of DACS switches must be coordinated so that if, for example, a particular facility is to be routed without switching from New York to Los Angeles, the facility is connected through each intermediate DACS along the route.
The toll administration system 405 is used to send control messages 15 over link 415 to toll switch 407. These control messages define the role of each of ~i the facilities connected to the toll switch 407 so that the destination of each facility terminating on the toll switch is defined within the toll switch 407 and that the trunk groups connected to that facility are properly identified in terms of that destination.
J FIG. 2 shows how the configuration of FIG. 1 is changed in accordance ~`
!il 20 with the principles of this invention. A combined administration system 500 sends a combined control message to a modified toll toll switch. The modified toll switch - -comprises memo~ and prograrns for controlling the DACS as well as the toll switch Toll switch 507 then sends DACS control messages over link 511 to DACS 503 arranged for control from the tolI switch 507. The facilities 413 interconnecting the 25 DACS 503 and toll switch 507 are unchanged from the facilities interconnecting DACS switch 403 and toll switch 417 of the configuration of FIG. 1. In addition,toll switch 507 can generate its own control messages to DACS 503 based on signaling messages received by toll switch 507, based on toll switch 507's analysis of traffio, and its analysis of messages received from other toll switches reflecting 30 facility outage or emergency traffic conditions. In response to these messages and -toll switch 507's own traffic analysis, toll switch 507 sends a series of pre-planned, or, alternatively, program-derived, DACS control messages over link 511 to change ~ `
the configuration of the DACS to meet the special needs of the network because of special traffic condidons or facilities outages.

~ -~, ,.. .. -~ . "- - ", , - ". ., . .~ . .

.,~ . . ., ~. , ,. - ~ ,: . . . .

.G ~ L 3 FIG. 3, representing the prior art as weli as the configruration for this . invention, is a block diagram illustrating the interconnections between customers, local and tandem switches, the digital access and c~oss connect system (DACS~, and toll switches. The small customers 110 are connected to toll switches 102 via one or ` 5 more local and tandem switches 106 and a DACS 104. Large customers 108 may be directly connected to DACS 104, thence to the toll switch 102. llle toll switch 102 performs all of its switching at a 64 kilobit digital signal Q (DS0) level and is ` `~ connected to the DACS via signals at a 1.544 megabit rate, the digital signal 1 ~DS 1 ) ` rate. Each DSl signal carries 24 DS0 signals. The DACS is arranged to handle both 10 DSl signals and digital signaling 3 (DS3) signals which are at a 45 megabit rate and ; -comprise 28 DSl channels. In relatively rare circumstances, the local or tandem ~-switch may go directly to the toll switch 102 via a DSl facility, but in general all ; ~ facilities to toll switch switching network 102 are from an associated DACS 104 which offers flexibility by allowing DSl facilities to be interconnected. The DACSs ' ' 15 are connected to other DACSs for carrying the long haul traffic of the toll switching network and these other DACSs are then in turn connected to other toll switch switching networks similar to 102, and to large customer premises similar to 108 and local or tarldem switches similar to 106. Large customers can directly access the ~j DACS in order to bypass the switching performed by the local and tandem switching 20 network when the services provided by this network are not required. The facilities `~1; from these large customers may be either private lines, i.e., connections which are not switched but terminate to another large customer prernises Iocation, or switched network access lines for giving large customers access to the toll switch switching P network 102 for connection to other locations of the large customer.
~, 25 A DSl facility interconnecting a DACS and a toll switch is generally connected within the toll switch to a bundled group of 24 trunks which are all or part of a trunk group having a comrnon destination. The DSl input is converted in thetoll switch into 24 DS0 signals, each representing one speech channel or one data , channel. A DS3 facility interconnecting two DACSs is broken up into DSl facilities ` ~j 3Q prior to connection to the toll switch which can treat each incoming DS 1 facility as a separate bundled group of trunks. The DSl and DS3 facilities interconnecting twoDACSs may be carried over much larger bandwidth facilities such as a fiber opticpair which can carry many DS3 facilities.
In rare instances, the two switches interconnected by a DSl facility treat 35 the 24 channels as being members of two separate ~mk groups, used for accessing ~' different destinations.
':1 .
~1 .
...
.' .'`J: ~
~";. ~ .
: .` ' : .

-''',' " ~ ' ' ~ ,` ' ' -' ' ':: ' , .
~"'.;.' .. :: ' :

2 ~

.: :
FIG. 4 is a block diagram of a toll switch such as the 4 ESSTM toll switch .
described in The Bell System Technical Journal, Vol. 56, No. 7, pages 1015-1320,September 1977. It is connected to a DACS via a fac;lity interface 202 for accepting ; facility DS 1 signals from the DACS and delivering DS0 signals to a switching :
5 network 204. The DS l signals are derivable from DS3 or other higher bandwidthfacility signals of the DACS, and are switched in the DACS to provide transmission facilities to the connected toll switch, local switch or private customer. The DS0 signals are trunk signals switched individually within the switching network 204 of ~:
. the toll switch. Switching network 204 is controlled by a main processor 206 which - 10 communicates with an auxiliary processor 208 having an attached data base 209. ~ ;
The auxiliary processor communicates with a signaling interface 210. This interface is connected to signal transfer points via connection 212 for passing signals necessary for setting up connections and is connected to a terminal of one of a large , customers via a connection 214 that traverses the switching network and the DACS. ~ .
15 The connection 214 is used to enable the large customer to signal directly to the toll switch when the customer wishes to establish a private line connection or change the private line or private network configuration. In addition, the toll switch is connected via connections 216 that terrninate on the auxiliary processor or the main processor to operation support systems (OSSs) for controlling the toll switch via 20 either a private line connection or a packet network. These operation supportsystems provide the data to the toll switch for establishing routing patterns, setting up trunk groups, delivering measurement reports from the toll switch to operation support systems for billing and for proper operation of the netwoTk.
FIG. 5, representing the prior art, is a block diagram of a DACS
25 showing a DACS fabric 302 connected to large customers, toll switches, local switches, and to other DACSs. The DACS switching fabric is under the control of a controller 304 which in turn communicates with a group of OSSs for controlling the DACS via a connection 306. In the prior art, these DACS OSSs which supply the data necessary to establish connections in a DACS are a completely separate set of ~ ~ -.~ 30 OSSs from the OSSs used for controlling operations in the toll switch. DACS OSSs receive inputs from customers requesting connection of facilities and receive requests from connecting local and from connected local switches requesting connection of facilities between the local switch and the associated toll switch. The - ~
j DACS terminates all the facilities that have been installed in a particular area, many ~ ~ -35 of which are not in use at any one time. In response to a request from a local switch or a private customer, communicated to an OSS by a service order, one of these : ~

' ~, '.~'.' ~ . `. ' ` ' , ' ' ` , , `'`.. ;``'. ~,' ', ~ ' ~ ' ` ` `"

-,'" ' ' ~ ` '` '' .~ ' , facilities that interconnects the appropriate points is selec~ed and connected via the DACS fabric to the toll switch. In other cases, a DACS facility is connected to another DACS that is connected to another toll switch. If an additional facility is needed between the two toll switches, each of the DACSs establishes a connection so - 5 that the p~eviously unused facility is now used to interconnect the two toll switches.
As can be seen from the above descriptions, the DACS which controls the switching of facilities and the toll switch which controls the connections set up j over these facilities are in the prior art controlled completely independently, even to the extent of receiving their basic control inputs from separate operation suppQrt 10 systems. By merging the control of the DACS and the toll switch, it is possible to create a system which has a far greater flexibility in the use of the facilities -interconnecting the DACS. Thus, it is possible to respond to network ~acility ', outages readily detected in the toll switches by switching to alternate facilities.
Similarly, it is possible to rearrange facilities to handle special traffic peaks such as `,J 15 those encountered in the case of facilities failures by reallocating facilities to :~ different routes. Further, by combining the OSSs that control the DACS with the -OSSs that control the toll switch, it is possible to substantially reduce the operating -.~ costs for these OSSs. Further, by having an integrated control of the DACS and the toll switch, it is possible to permit those large customers who use both private20 network services and public network services to have a single interface for signaling i their requests for changes in either or both the toll s~itch and the DACS.
: ~ FIG. 6 is a diagram of memory layouts in the toll switch for controlling DACS connections. Block 600 is a record of existing DACS connections. For each connection set up in the DACS, eight segments of a record such as 610, 620, 630,' $ 25 640, 650, and 660, are used to describe the connection. Within record 610, segments 611 and 616 specify the input and output terminal of the connection wi~hin . ~ the DACS. Segments 612 and 613 represent an equipment number and an ~¦ identification for the facility connected to the DACS input te~inal. In the example .
;,, of record 610, this is a customer equipment number (i.e., ian equipment identification ''~ 30 of the terminal on the customer's premises to which the DACS input terminal is : .
connected) and an identification of the customer. Segments 614 and 615 specify the $ identification and equipment number of the terminal to which the DACS output ~, j tenninal is connected. In the case of record 610, this is an identification of the ~-~ connected toll switch and the equipment number within that toll switch.
, 35 Segment 617 identifies a type of facility (for example, DS 1 or DS3) and segment 618 -~' is a pointer to a block such as auxiliary block 680 which contains additional .' . li '.J : ' ' .

"; " '.'.'~ '. : " , ` ',, ; 2~7~ L3 -.- - 10- .' :, inforrnation .
Shown in FIG. 6 are examples of memory layouts for different DACS
connections. Record 610 is for a customer to toll switch cormection; record 620 is for a connection between a toll switch and another (remote) DACS; record 630 is for 5 a connection between two remote DACSs; record 640 is for a connection between two premises of a customer; record 650 is for a connection between a local or tandem switch and a toll switch; and record 660 is for a connection between a customer and a remote DACS. ~ -A typical auxiliary block 680 contains an identification of the source and 10 destination, i.e., the two ends that are connected by facilities interconnected by one . or more DACSs, a trunk group identification for identifying the trunk group in the toll switch that is carried by the facility, and a trace of the DACSs connecting the source and destination and of the equipment locations within those DACSs that are connected. This block can be used so that a controlling toll switch may request a ~ -15 change in use of a facility by sending appropriate requests for controlling other DACSs that are in series with the facility to other toll switches controllin~ those -DACSs.
;~ FIG. 6 shows another block 690 used for storing data for pre-planned configuration changes. For example, if it is recognized by the network ~ -20 administration staff that if a par~icular facility fails, a series of facility reconfigurations is required, then such information can be stored in one of the toll switches used for controlling the DACS. This toll switch receives a message indicating that the subject facility has failed. In response to receipt of this message, a pre-planned series of control messages 695 are sent to toll switches for controlling 25 the DACS associated with those facilities which require reconfiguration.
.~ Reconfiguration may also be performed in response to measurement by the system that traffic exceeds or is less than ce~tain pre-planned thresholds; in response to the -1 recognition of this state, a pre-planned series of facility reconfigurations should be :, performed. The control messages can be stored dLrectly or can be derived by 30 program means.
FIG. 7 is a flow diagram of actions performed under the control of ; ! control processors of the toll switch for controlling an associated DAS: S. The toll switch receives a service order message (action block 701). This message is ; analyzed to see if it requires a connection within the toll switch. Such a connection 35 may be required if, for exarnple, only a DS0 channel is to be provided for a given '~2 customer (the DACS 3 and DACS 4 systems, for example, cannot switch DS0 ~?!
i ., .
., -i ~ - .: .
, ,. < ::
. ,.. , . ~ . , ~ ~. ; ~ : - . - ..... , . :

channels). If the service order represents the creation of a new ~unk group for serving customer dialed calls, then toll switch connections are also required inconnection with this service order. In either such case, the toll switch memory must be initialized, in one case to reflect a semi-permanent connection, in the other case to S c}eate the inforrnation representing the new tr mk group (action block 705). Next, the control memory (previously described with respect to FIG. 6) must be initialized ; ~ in the toll switch to reflect the required DACS connections ~action block 7~)7).
Messages for requesting these DACS connections are then p:repared and transmitted to the DACS (action block 709) in order that the DACS set up the connections " 10 specified by the service order. ~ -As indicated previously, the configuration of the present invention is , sufficiently flexible so that it can respond to requests other than service orders. The toll switch can receive customer rearrangement request messages to rearrange facilities interconnections for customers with large private networks and to rearrange , 15 these facilities either through DACS switches or through connections set up within -~', the toll switch or through a combination of both. The same basic arrangement is used for setting up the connections as previously described.
I~i In addition as previously described, the toll switch can detect conditions ;3 from received messages indicating a facilities outage or some other reason for 20 requesting a facilities reconfiguration (action block 721). This request is then converted into a plan of the necessary changes in the DACS and in one or more toll switches (action block 723). As indicated above, in the present configuration these changes are stored as a series of pre-planned messages for requesting changes in the DACS. Alternatively, the controller function for the DACS may be absorbed 25 completely into the switch, and the DACS control messages become direct memory writes for establishing or disconnecting specific paths in the DACS switching fabric.
Alternatively, traffic algorithms can be used to derive the changes independently. If the changes involve different assignments of facilities connected to the toll switch, then it may be necessary to flush calls from trunk groups cuTrently -30 using facilities which are being reconfigured (action block 725) by refusing all new calls for the facility until all the existing calls have ended. Thereafter, the same actions previously described for initializing the toll switch memory, the DACS
control memory, and transmitting control messages to the DACS are performed.
,' With the configuration in accordance with the principles of this35 invention, the number of DACS switch operations performed per unit time is increased substantially and is likely to be increased even further as full advantage is ' ~
, ~

!.1 ; ', ' :
~''~ ' , '~.

: ~ 1 , .: , .. .. . ' ' i 3 ~ 12-r i~ taken of this arrangement. It is therefore necessary to modiEy the control link to the `~ DACS controller to allow for a higher volume of control messages. The control link ` to the DACS controller is connected either to the output of the auxiliary ~i~ processor 208 (FIG. 5) or directly to the interface bus 216 connected to both the 5 main processor and the auxiliary processor 208. The capacity of the interface bus 216 is higher so that this is the preferred long term solultion. Further, in order to increase the number of connections that can be made by the DACS, it is desirable to preprocess the connections orders and send to the DACS specific connection ^~ requests. This preprocessing is performed by the auxiliary processor 208 in response .-', 10 to service order messages from the operation support system.
While in this specific embodiment, a toll switch is used to control the ;~ DACS, it is also possible to control the DACS similarly from a local or tandem switch.
~ The description which follows relates to the integration of an .!~ 15 interconnection arrangement, e.g., a DACS, with a local central of fice switching system. In the specific embodiment described, the interconnection alrangement is -based generally on the AT&T DACS IV digital access and crossconnect system described in the publication AT&T 365-301-004 "DACS IV (Digital Access and ;l~ Crossconnect System IV); the central of fice switching system is based generally on 20 the AT&T SESS(~ Switch described in the AT&T Technical Journal, July-August 1985, Vol. 64, No. 6, Part 2. The description is arranged in three parts: (I) the i~ AT&T SESS Switch is described as it exists in the prior art; (2) modifications and 1 additions to the SESS Switch are then described which provide the integration of an ,l interconnection arrangement with a switching system, under a common control 25 structure, in a central of fice wire center C0-2000 (FIGS. 1 la and 1 lb); and (3) a further embodiment (FIG. 12) is then described where the interconnection arrangement is implemented using add/drop multiplexers connected in a fiber ring in a distributed architecture rather than using a DACS.
.~ Prior Art Systcm lOûO
FIGS. 8-10 are used to desc~ibe the plior a~t switching system 1000.
U. S. Patent 4,323,843 issued to H. J. Beuscher et al. on March 30, 1982 and U. S. -Patent 4,683,584 issued to S. Chang et al. on July 27, 1987 describe aspects of the system in detail.
-! Switching system 1000 (FIG. 8) has three major components: an - -~
` 35 administrative module (AM) 4000 that provides systemwide administration, ~ ~ -maintenance, and resource allocation; a communications module (CM) 2000 that . . .

;';

provides a ll.~b for distributing and switching voice or digital data, control information, and synchroni~ation signals; and a number of switching modules ~r` (SMs) 3000-1, 3000-N that perform local switching and control functions and that provide interfaces to subscriber lines and interexchange circuits.
AM 4000 provides the system-level interfaces required to operate, administer, and maintain sys~em 1000. It performs functions that can most ~-~, economically be done globally, such as common resource allocation and maintenance control. For reliability, AM 4000 includes fully duplicated processors and the two processors work in an activefstandby configuration. In normal operation ~ -:
10 the active processor has control and, at the same time, keeps the data in the standby processor up to date. Thus when a fault occurs in the active processor, the standby processor is switched into service with no loss of data.
AM 4000 performs many call-processing support functions, including systemwide craft maintenance access, diagnostic and exercise control and 15 scheduling, software recovery and initialization, and certain fault-recovery and . er~or-detection functions best done on a centralized basis. Within AM 4000, therei is eIror-checking circuitry for detecting and isolating faults. AM 4000 also performs administrative functions and provides software access to external data links and to disk storage (not shown).
The basic function of CM 2000 (E7IG. 9) is to provide consistent -communications between the SMs, and between AM 4000 and the SMs. A messæge , switch (MSGS) 2020 transfers call-processing and administrative messages between the SMs and AM 4000, and between any two SMs. MSGS 2020 performs a packet-switching function within system 1000 utilizing the well-known X.25 level-2 25 protocol to transfer control messages through CM 20l,iO and its terminating network control and timing (NCT) links 100-1, 100-N. This protocol includes error detection, positive message acknowledgment, and message retransmission in the `~ event of a transmission error. A network clock 2030 provides the clock signals that -~ synchronize the time-division network. Clock 2030 is synchronized through an `~
;` 30 external source or runs on an internal reference basis with periodic updating.
System 1000 uses a time-space-time architecture. As illustrated in ~ . -`. FIG. 10, a time-slot interchange unit (TSIU) in each SM performs the time-division ~! switching; a time-multiplexed switch (I~MS,~ 2010 in CM 2U00 (FIG. 9) perforrns the - -~
time-shared space-division switching. At each interface unit (FIG. 10) the outputs : `
35 from lines and trunks are converted into 16-bit time slots. These bits are used for signaling, control, and parity, and for binary-coded voice or data. The time slots are ~ -, .` :' ' .

switched through ~he TSIU and time-multiplexed on NCT l;nks to TMS 2010.
TMS 2010 (FIG. 9) is a single-stage switching network that provides the `~ digital paths for switched connections between the modules and for control messages among modules. TMS 2010 interconnects the modules via the NCT links. Each 5 NCT link carries 256 channels (time slots) of multiplexed data in a 32.768-Mb/s .~j serial bit stream. One of the time slots carries control messages, and the remaining 255 time slots carry digitized voice or data. Two NCT links are associated with each switching module, thus allowing 512 time slots to be routed to and from TMS 2010. (However, only a single line 100- 1 is shown in the drawing to 10 represent both NCT links between SM 3000-1 and CM 2000.) Setting up a path ' d between a line or trunk on two SMs involves finding an idle time slot on one of the NCT links to each SM. A path is then set up through TMS 2010 between the two NCT links using the selected time slot. The TSIU in each SM establishes a path between the selected NCT time slot and the peripheral time slot associated with the . 15 line or trunk. (Since the paths are bidirectional, one NCT time slot is needed for -., each direction of transmission. In the present embodiment however, the time slots 3 for the two directions are selected to have the same number.) ', One of the signaling bits of the 16-bit time slots on the NCT links to TMS 2010, referred to as the E-bit, is used for continuity verification between SMs 20 after an inter-SM call has been set up through TMS 2010. For example, after a call between SM 3000- 1 and SM 3000-N has been set up through TMS 2010 using a particular time slot, both SM 3000-1 and SM 30û0-N begin transmitting a logic one ~ E-bit in the particular time slot as a continuity signal and both also begin scanning ;, the E-bit of the particular time slot received from the other SM. The call setup 25 procedure is not considered complete until both SM 3000-1 and SM 3000-N have detected the E-bit continuity signal from the other SM.
, SMssuchasSM3000-1 (FIG. 10)providecall-processingintelligence, the first stage of switching network, and line and trunk terminals. SMs differ in the ~ -types and quantities of interface equipment they contain, depending upon the -~
. 30 characteristics of the lines or trunks terminating thereon. Certain equipment is however, common to all SMs. The common equipment includes a link j interface 3030, a TSIU 3010, and a module control unit 3020. Link interface 3030 provides a two-way interface between each SM and TMS 2010 in CM 2000. Module control unit 3020 controls call processing, call distribution, and maintenance ! 35 functions. A variety of interface units 3041, 3042 are available in system 1000.
Line units provide interfaces to analog lines. Trunk units provide interfaces to ~ ~ ~

," , : ':

__ f~ 3 , - 15 -. . ~
;`'i analog trunks. Digital line trunk units provide interfaces to digital trunks and remote SMs, while digital carrier line units provide the interface to digital carrier systems.
Integrated services line units provide interfaces to digital ISDN lines. Each SM can ` accommodate any mixture of these units, with up to 510 channels. Two time slots . ~ are used for control.
TSIU 3010 includes a signal processor, which handles address and signaling information and a control interface, which distributes control signals to and from the interface units. TSIU 3010 switches time slots between the interface units in an SM and connects time slots from the interface units to time slots on NCT links.
10 TSIU 3010 switches 512 time slots--256 from each of the NCT links between ,'jf SM 3000- 1 and CM 2000--and 512 peripheral time slots from the interface units.
TSIU 3010 can connect any of its 512 peripheral time slots to any other peripheral time slot, or to any time slot of either NCI' link to CM 2000.
'i Central Of fice Wire Center C0-2000 f 15 FIGS. 1 la and l lb comprise a diagram of an architecture for a central , of fice wire center C0-2000 where a switching system and a DACS are integrated ' under the comrnon control of an administrative module (AM) 2052. In FIGS. 1 la and l lb, the DACS functionality is implemented by a digital networking unit ~1 ", (DNU) 2059. TheotherelementsinFIGS. llaand 1lbareelementsofaswitching system based on the architecture of system 1000 ~rFIG. 8) but with modifications and additions as described herein.
C0-2000 includes one or more switching modules, SM-20~, SM-2000', which, like the conventional switching modules of the prior art system, ;l perform time-switching functions under the control of a dis~ibuted module control ~ `
unit or switching module processor (SMP) 2041,2042. However, switching modules SM-2000 and SM-2000' are substar.tially larger than conventional - -switching modules and can switch approximately 16K peripheral time slots and 16K -, network time slots. Also included as part of the switching system is a remote - - --switching module RSM-2000, controlled by SMP 2043, and a remote terminal RT-2000, both located at a distance from C0-2000, and interconnected with C0-2000 via fiber links 2121 and 2122. Conventional switching modules such as SM 2050 controlled by SMP 2044 and providing service to lines and tranks 2049, may also be -~ included in the same system.
- SM-2û00 includes a time-slot interchange unit (TSIU) 2031 which 35 switches time slots between interface units connected via peripheral control and - ` -~
? timing ~CI) links 2080, 2081,2071, and connects time slots from the peripheral ~ ~:

:'~1 ~ ` " "`"`,` '`''`

:

n interface WlitS to time slots on network control and timing (NCT) links 2056 to communications module 2055. Access interface unit (AIU) 2078 provides the system interface to lines 2112 including POTS (plain old telephone service), ISDN
(integrated services digital network) and special lines 2112. AIU 2M8 provides the 5 typical functionality (battery, overvoltage, ringing, supervision, coding/decoding, hybrid, testing) for analog lines, and terminates the standard B and D channels for ISDN lines. Special lines include lines to private branch exchanges, foreign exchanges, etc. Tr~mk unit (TIU) 2076 provides the system interface to trunks 2111 at DSl and OC-l/OC-3 rates (Table 1). The PCT links are terminated at both ends - -.~ 10 by peripheral link interfaces (PLIs). Note that DNU 2059 is connected as a ;l peripheral unit. ~
' - . ' , . :.
TRANSMISSION RATES
DS-0 = 1 voice circuit = 64 kb/s DS-l = 24 voice circuits = 1.544 Mb/s : -,: ~ ...
DS-3 = 672 (28 x 24) voice circuits = 44.736 Mb/s OC-l = 672 voice circuits = STS-l = 51.84 Mb/s ~ ;:
., - . . .
OC-3 = 2016 (3 X 672) voice circuits = STS-3 = 155.520 Mb/s :~~ OC-12 = 8064 (4 X 2016) channels = STS-12 = 6æ.080 Mb/s VTl.5 = 1.728 Mb/s Sonet envelope containing a DSl rate signal.
Table 1 . ~ - - . --3 In the present exemplary embodiment, the NCT and PCT fiber optic linkstransmit data at an OC-3 rate and each comprise 2016 time slots. (Alternatively,25 three links at an OC- l rate may replace one link at an OC-3 rate.) The number of NCT links is engineered dependent on the amount of inter-module traffic. SM-2000can connect any of its peripheral time slots to any other peripheral time slot, or to ~i any of the network time slots on NCT links 2056. Within CM 2055, a given NCT
3 link 2056 is divided into lines each comprising 256 time slots, for switching by a 30 time-multiplexed, space-division switch to the other switching modules.
DNU 2059, based on the above-referenced DACS IV, includes a DACS
: controller 2061, which operates in response to commands from AM 2054 via ~ -CM 2055 and data link 2058, to control the operation of a DACS interconnection fabric 2û62. Fabric 2062 has a plurality of ports and provides crossconnections ; ~ -35 between ports at DSl, DS3, OC-3 and OC-12 rates, for example, among interface ~: .-~ .
,~ .

UllitS such as ~mits 2063-2069. DNU 2059 is used to perform conventional crossconnection functions, performed by separate DACS sy stems in the prior art,such as interconnecting DSls between other switching systems and crossconnect systems. DNU 2059 also interconnects DS 1 multiplexes from transmission facilities 2060, 2070 via PCT links to SM-20Q0 and SM-20lD0' for DS0 switching.
:~ In some applications, all inter-office trunks may be receivecl by DNU 2059 rather `.: than by TIUs within SM-2000 or SM-2000'. DNU 2059 is also used to interconnect remote terminal Rl'-2000, via a fiber link 2122 in accordance with Bellcore ` Technical Reference TR303, with SM-2Q00. The number of PCT links between - 10 DNU 2059 and SM-2000 is engineered based on the required traffic.
DNU 2059 is usable to provide semi-permanent connectivity between SM-2000 and SM-2000' for use in handling some of the inter-module call traffic, without requiring the use of the individually switched connections through CM 2055. For example, in one alternative all inter-module calls are routed through DNU 2059, and CM 2055 is used only when the semi-permanent connectivity ~, through DNU 2059 is all being used for other calls. - ~ ~
:1 RT-2000 includes an AIU 2117 for interfacing POTS, ISDN, and special ~ ~ -,', lines 2118 with time slots on link 2122. AIU 2117 has time slot interchange , capability such that a group of 24 special lines, for example, are combined within a ~ .
i~ 20 single DSl multiplex on link 2122 and crossconnected by DNU 2059 with a transmission facility to another switching system, without being switched through ~, SM-2000. Lines2118mayincludemetallicand/oropticalfiberlines. AIU2117,. . . .
operates as a digital loop carrier system in the manner of the AT&T SLC~ calliersystems. All the circuits from RT-2000 that are to be individually switched by SM~
,' 25 2000 are crossconnected via fabric 2062 to interface unit 2063, which performs framing functions and terminates a derived data link for control messages from AIU 2117. Interface unit 2063 also performs overhead processing for SONET
streams received via facilities 2060,2070. The message processing from such streams is performed by SMP 2041.
RSM-2000, which is substantially identical to SM-2000, is connected via fiber links 2121 and DNU 2059 to SM-2000 which operates as a host switching module in the manner described in U. S. Patent 4,550,404 issued to M. M. Chodrowfl~ et al., on October 29,1985. Alternatively, RSM-2000 may be connected directly via ii links 2121 to CM 2055 for operation as an optical remote module.
,, . ~ ~:: . " :, s'~ '.
x~

AM 2052 performs the functions of AM 40û0 (FIG. 8) of the prior art system, and further includes a processor referred to as a local operations manager (LOM) 2053 to interface operations support systems (OSSs) for both switching ` systems and crossconnect systems as well as to the craft interface used in -`~ 5 controlling, in an integrated fashion, the operations, adminisltration, maintenance, and provisioning (OAM&P) functions, for both the switchinlg system and the , interconnect arrangement (DNU 2059).
An illustrative method of the invention is used in a central of fice wire center C0-2000 (FI~S. 1 la and 1 lb) including an interconnect arrangement ~, 10 (DNU 2059) terminating transmission facilities (2060,2070), and further including a ~ -switching system including peripheral units (AIUs, TIUs) for interfacing peripheral circuits (lines, trunks) with the switching system. The switching system also includes switching units (TSIUs 2031,2032) foT providing switched communication ~ -among the peripheral circuits in response to calls to and from the peripheral circuits.
, 15 The wire center further includes a control means (AM 2052) common to the interconnect arrangement and the switching system. In response to the control means, the interconnect arrangement interconnects the switching system and at least one multiplex of circuits (e.g., a DSl multiplex comprising 24 circuits) of at least -3 one of the transrnission facilities. Also in response to the control means, the 20 switching system establishes calls to and from individual circuits of that multiplex.
The interconnect aIrangement also interconnects units of the switching ;t system. For example, ~he interconnect arrangement interconnects a peripheral anit (AIU 2117) at a remote terminal (RT-2000) and a switching unit ~TSIU 2031) at the ;l central of fice wire center. Alternatively, the interconnect arrangement interconnects 25 a peripheral unit and a switching unit that are both located at the central of fice wire center. The interconnect arrangement is usable to interconnect two switching units, ,;1 e.g., a host switching unit (TSIU 2031) at the central of fice wire center and a remote switching unit (TSIU 2033) at a distance from the wire center, or two distributed switch units (TSIUs 2031,2032) at the wire center. The switching system further `~
30 includes a central switch (CM 2055) for providing switched communication between 1 differentswitchingunits(TSIUs2031,2032).
-~ An illustrative combination in accordance with the invention comprises a switching system, an interconnect means (DNU 2059), and control means (AM 2052) common to the switching system and the interconnect means. The 35 switching system selectively interconnects ones of a plurality of con~nunication i`~ circuits (DS0 circuits~. The interconnect means selectively interconnec~s ones of a -~

1 . .
,:, . . -.
"~ ' .. i '- ' ~
. 1 ..

:~
:1; :: :: ~
:`~`: : :

; 3 .

. . .

plurality of communication multiplexes (e.g., DS 1 multiplexes each comprising 24 DS0 circuits). A first of the multiplexes (a DSl on PCT link 2071) is connected to the switching system. The control means controls both the interconnection by the`~ interconnect means of ones of the multiplexes, and the establishment by the 5 switching system of calls to and from individual ones of the circuits of the first multiplex.
- The control means includes a comrnon operations, administration, maintenance, and p~ovisioning system for the switching system and the interconnect .' means. The interconnect means has a plurality of ports (connected to IUs 2063-;~ 10 2069) and interconnect control means (DACS controller 2061) for controlling the interconnection of the ports. The interconnect means and the switching system are colocated at a central of fice wire center (C0-2000).
A second multiplex (a DSl on link 2122) conveys information to and from peripheral communication circuits (lines 2118). The control means controls the ~ -15 Interconnection by the interconnect means of the first and second multiplexes, and -the establishment by the switching system of calls to and from individual ones of the -peripheral circuits via the first multiplex, the interconnect means, and the second ~ ~
~ multiplex. - ~-:
,, A third multiplex (a DS 1 on link 2060) and a fourth multiplex (a DSl on -20 link 2070) are not comlected to the switching system. The control means controls the interconnection of the third and fourth multiplexes. The third and fourth multiplexes may be connected to other switching systems and interconnect means that are independent of the control means. -Add/Drop Fiber Ring Architecture ;~ 25 FIG. 12isadiagramofanalternativetothearchitectureofFIGS. lla ~J and 1 lb. In FIG. 12, the function of the interconnect arrangement, ~performed by :~ DNU 2059 in FIGS. 11 a and 11b) is performed by a plurality of add/drop , multiplexe.r units DDM-2000 interconnected in a ring. In the present example, the ;~
ring operates at an OC-12 rate. A multiplexer unit DDM-2000 is used to receive - - `
transmission facilities, e.g., 2060, 2061, at DSl, DS3, OC-3 and OC-12, and performs bandwidth shedding, add/drop multiplexing, and SONET overhead ~ .
processing as required. The add/drop fimctionality of a particular unit DDM-2000 is programmed by the SMP of the associated SM-2000, under the overall control of AM 2052. DS 1 multiplexes received on transrnission facilities 2060-2069, or from remote terminals RT-2000 or remote switching modules RSM-2000, are connectable '~, via the ring to any one of the SM-2000s for switching. The crossconnection of }il ' " ~`

~'7~ 3 ~ -.... ,~ .:

multiplexes may by performed within the DDM-2000s or the SM-2000s. - ~:
'` !
,;~, ".
~, .
' ', ~

:'.' ~ ' "

S . ' .
'; :`
:~, '~ ' '' ''.
,, ' ':',, '~' ' . . ' :,' ~ -'~. :, .:
.; ' '.... ' " ' -. ' ~.,'.''','`','',',,''.,'"'`..
/~ ;'~ ...... `

; "`"`''"~.

'` l -- ', `:~

''.,~ ~, : , ' , . '; '.
-.' : : , .: . : ~

Claims (30)

1. In combination, a switching system for selectively interconnecting ones of a plurality of communication circuits, interconnect means for selectively interconnecting ones of a plurality of communication circuit multiplexes, said plurality of multiplexes comprising a first multiplex connected to said switching system, and control means, common to said switching system and said interconnect means, for controlling both the interconnection by said interconnect means of ones of said plurality of multiplexes, and the establishment by said switching system of calls to and from individual ones of said circuits of said first multiplex.

2. The combination of claim 1 wherein said interconnect means comprises a crossconnect system.

3. The combination of claim 1 wherein said interconnect means comprises a plurality of units interconnected in a ring configuration.

4. The combination of claim 1 wherein said control means comprises a common operations, administration, maintenance, and provisioning system for saidswitching system and said interconnect means.

5. The combination of claim 1 wherein said interconnect means has a plurality of ports connected to said plurality of multiplexes, and comprises interconnect control means responsive to said common control means for controlling the interconnection by said interconnect means of ones of said ports.

6. The combination of claim 1 wherein said interconnect means is colocated with said switching system at a central office wire center.

7. The combination of claim 1 wherein said plurality of multiplexes further comprises a second multiplex conveying information to and from a plurality of peripheral communication circuits comprising at least one of lines and trunks, and said control means controls the interconnection by said interconnect means of said first and second multiplexes, and the establishment by said switching system of said calls to and from individual ones of said peripheral communication circuits via said first multiplex, said interconnect means, and said second multiplex.

8. The combination of claim 7 wherein said plurality of multiplexes includes third and fourth multiplexes that are not connected to said switching system, and said control means controls the interconnection by said interconnectmeans of said third and fourth multiplexes.

9. The combination of claim 8 wherein said third multiplex is connected to a switching system independent from said control means.

10. The combination of claim 9 wherein said fourth multiplex is connected to interconnect means independent from said control means.

11. The combination of claim 9 wherein said fourth multiplex is connected to a second switching system independent from said control means.

12. The combination of claim 8 wherein said third multiplex is connected to an interconnect means independent from said control means and said fourth multiplex is connected to a second interconnect means independent from said control means.

13. The combination of claim 7 wherein said peripheral communication circuits are customer lines.

14. The combination of claim 7 wherein said peripheral communication circuits are trunks.

15. The combination of claim 7 wherein said switching system comprises a plurality of distributed switch means.

16. The combination of claim 15 wherein said switching system further comprises central switch means for selectively interconnecting individual, switched communication circuits between ones of said distributed switch means.

17. The combination of claim 16 wherein said control means is responsive to ones of said calls for controlling said distributed switch means and said central switch means to switch said ones of said calls via said central switch means.

18. The combination of claim 15 wherein said switching system further comprises remote switch means interconnected with said interconnect means via said second multiplex, wherein said first multiplex is connected to one of said distributed switch means, and said control means is responsive to ones of said calls for controlling said remote and said one distributed switch means to switch said ones of said calls via said remote switch means, said second multiplex, said interconnect means, said first multiplex, and said one distributed switch means.

19. The combination of claim 15 wherein said switching system further comprises peripheral interface means for interfacing a plurality of said peripheral communication circuits and interconnected with said interconnect means via said second multiplex, wherein said first multiplex is connected to one of said distributed switch means, and said control means is responsive to ones of said calls for controlling said one distributed switch means to switch said ones of said calls via said peripheral interface means, said second multiplex, said interconnect means, said first multiplex, and said one distributed switch means.

20. The combination of claim 19 wherein said plurality of distributed switch means are at a central office and said peripheral interface means is at a remote terminal.

21. The combination of claim 20 wherein said peripheral interface means is a digital loop carrier system.

22. The combination of claim 15 wherein said interconnect means comprises a crossconnect system.

23. The combination of claim 15 wherein said interconnect means comprises a plurality of add/drop multiplexer units each connected to an associated one of said distributed switch means.

24. The combination of claim 23 wherein said plurality of units are interconnected in a ring configuration.

25. The combination of claim 15 wherein said control means comprises a plurality of distributed control means each associated with one of said distributed switch means.

26. The combination of claim 25 wherein said control means further comprises central control means which cooperates with said plurality of distributed control means to control the establishment of said calls.

27. The combination of claim 26 wherein said interconnect means comprises a plurality of ports connected to said plurality of multiplexes, and interconnect control means responsive to said central control means for controlling the interconnection by said interconnect means of ones of said ports.

28. The combination of claim 25 wherein said interconnect means comprises a crossconnect system.

29. The combination of claim 25 wherein said interconnect means comprises a plurality of add/drop multiplexer units each connected to an associated one of said distributed switch means and controlled by the associated one of said distributed control means.

30. The combination of claim 29 wherein said plurality of units are interconnected in a ring configuration.