WO1998030058A2

WO1998030058A2 - Method and apparatus to interconnect two or more cross-connects into a single pcm network

Info

Publication number: WO1998030058A2
Application number: PCT/US1997/023968
Authority: WO
Inventors: Gregory S. Lovelace; Peter H. Bice; Clayton D. Utley; Amanda G. Noe; David M. Smith
Original assignee: Alcatel Usa Sourcing, L.P.
Priority date: 1996-12-31
Filing date: 1997-12-18
Publication date: 1998-07-09
Also published as: AU5721698A; CA2276605A1; WO1998030058A3; EP0950336A2

Abstract

A telecommunications network is provided. The telecommunications network includes a fiber optic conductor (20, 22) and at least two digital cross-connect systems (12, 14, 16, 18). Each digital cross-connect system (12, 14, 16, 18) has M network interface input ports and N network interface output ports, where M and N are integers that are greater than zero. The digital cross-connect systems (12, 14, 16, 18) are interconnected by the data transmission medium (20, 22). Any one of M network interface input ports of any digital cross-connect system (12, 14, 16, 18) may be connected to any one of N network interface output ports of any other digital cross-connect system (12, 14, 16, 18) through the data transmission medium (20, 22).

Description

METHOD AND APPARATUS TO INTERCONNECT TWO OR MORE CROSS-CONNECTS INTO A SINGLE PCM NETWORK

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of telecommunications, and more particularly to a method and apparatus to interconnect two or more cross- connects into a single pulse code modulation (PCM) network.

BACKGROUND OF THE INVENTION

A telecommunication system may be used to transfer data between two telecommunications systems interfaces. Various data transmission media may be used to transfer the data. For example, the call may be placed by a cellular telephone using microwave frequency electromagnetic radiation. This call may then be connected to a land-based system which may use copper or fiber optic conductors. The call may then be routed through a satellite communications system which uses high frequency electromagnetic radiation, or through a submarine communication system that uses copper or fiber optic conductors.

Regardless of the media used to transmit the telecommunications data, the transfer of telecommunications data between two telecommunication system interfaces typically requires connection through one or more switches. A digital cross-connect is a specialized telecommunications switch that is capable of connecting any of a large number of inputs to any of a large number of outputs. An example of a modern digital cross-connect system is provided by U.S. Patent 5,436,890 to Read, et al . , entitled "Integrated Multi-rate Cross-Connect System, " assigned to DSC Communications Corporation, issued July 25, 1995 (hereinafter "Read" ) . Such digital cross-connect systems may include a plurality of devices that define the M network interface input ports and the N network interface output ports of the switch Although digital cross-connect systems provide many advantages over prior systems, one problem that may be encountered using digital cross-connect systems involves the limitation of digital cross-connect system resources that may be required to interconnect multiple digital cross-connect systems. For example, if a call requires routing through two digital cross- connect systems, it is necessary to use an input port and an output port on both digital cross-connect switches. Thus, twice as many digital cross-connect switch resources must be used to connect the call through two digital cross-connect systems than would be required if the connection could be made with a single digital cross-connect. This problem may be compounded when a large number of digital cross- connect systems are interconnected. Resolution of this problem would typically require reconnecting the digital cross-connect systems such that digital cross- connect switch resources may be used effectively. SUMMARY OF THE INVENTION

Therefore a need has arisen for a method and apparatus to interconnect two or more cross-connects into a single pulse code modulated (PCM) network. Accordingly, the present invention provides a method and apparatus for interconnecting two or more digital cross-connect systems into a single PCM network that does not require reconfiguration of switch connections to improve the efficient use of system resources.

A telecommunications network is provided. The telecommunications network includes a fiber optic conductor and at least two digital cross-connect systems. Each digital cross-connect system has M network interface input ports and N network interface output ports, where M and N are integers that are greater than zero. The digital cross-connect systems are interconnected by the data transmission medium. Any one of M network interface input ports of any digital cross-connect system may be connected to any one of N network interface output ports of any other digital cross-connect system through the data transmission medium.

The present invention provides many technical advantages. One important technical advantage of the present invention is that two or more digital cross- connect systems may be interconnected to form a single PCM network without reconfiguring the digital cross- connect switch input port and output port connections . The present invention allows digital cross-connect system resources to be used efficiently without reconfiguring the digital cross-connect system connections .

Another important technical advantage of the present invention is that it does not consume two network interface ports of each digital cross connect to make connections from an input on a first cross connect to an output on a second cross connect. The present invention instead uses a drop and connect matrix fabric and ring bus configuration to route telecommunications traffic between digital cross- connect systems.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:

FIGURE la is a block diagram of four digital cross-connect systems connected as a single PCM network;

FIGURE lb is a block diagram of four digital cross-connect systems connected as a single PCM network in a non-blocking configuration; FIGURE 2 shows a block diagram of a digital cross-connect matrix connection for one plane of one digital cross-connect matrix;

FIGURE 3 shows a detailed drawing of a block diagram of a digital cross-connect matrix connections; FIGURE 4 shows a schematic diagram of a digital matrix interface card embodying concepts of the present invention; FIGURE 5 shows a schematic diagram of a digital matrix multiplexer/demultiplexer card embodying concepts of the present invention;

FIGURE 6 shows a schematic diagram of a digital matrix card embodying concepts of the present invention;

FIGURE 7 shows a schematic diagram of a digital matrix interface/output card embodying concepts of the present invention; and FIGURE 8 shows a flow chart for a method for interconnecting two or more digital cross-connect systems into a single PCM network embodying concepts of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in the figures, like numerals being used to refer to like and corresponding parts of the various drawings. FIGURE la is an exemplary block diagram of a PCM network 10 that includes four interconnected digital cross-connect systems 12, 14, 16 and 18. PCM network 10 also includes a counterclockwise data transmission medium ring 20 and a clockwise data transmission medium ring 22, which form counter-rotating data transmission media rings.

Digital cross-connect systems 12, 14, 16, and 18 include high capacity switching matrices that are operable to connect any of a large number of inputs to any of a large number of outputs, such as shown in Read. Digital cross-connect systems 12, 14, 16, and 18 may utilize distributed administration processing, such that administration processing is performed at each digital cross-connect. Alternately, digital cross-connect systems 12, 14, 16, and 18 may utilize a centralized administration unit. A system database (not explicitly shown) containing information on the connections and status of each digital cross-connect system 12, 14, 16, and 18 in PCM network 10 is stored at and maintained by the administration system (not explicitly shown) of each digital cross-connect system 12, 14, 16, and 18. Alternately, the system database may be centrally stored. As taught in Read, each digital cross-connect system 12, 14, 16, and 18 may include 2 parallel planes having redundant processing capability. Counterclockwise data transmission medium ring 20 and clockwise data transmission medium ring 22 comprise a data transmission medium or data transmission media that are operable to carry digitally encoded PCM data. Counterclockwise data transmission medium ring 20 and clockwise data transmission medium ring 22 are characterized by a large data bandwidth, and comprise independent segments of data transmission media that couple each digital cross-connect system in PCM network 10. Counterclockwise data transmission medium ring 20 and clockwise data transmission medium ring 22 may comprise a copper conductor, a coaxial conductor, a fiber optic conductor, a microwave channel, or other suitable data transmission medium or media. In operation, digital cross-connect systems 12,

14, 16, and 18 are used to route telecommunications traffic. Local connections (not explicitly shown) are made to each of digital cross-connect systems 12, 14, 16, and 18, such that any of M network interface input connections to a digital cross-connect system may be connected to any of N network interface output connections of that digital cross-connect system. In addition, any of the M network interface input connections to one of digital cross-connect systems 12, 14, 16, or 18 may be coupled to any of the N network interface output connections of another of digital cross-connect systems 12, 14, 16, and 18.

For example, digital cross-connect systems 12, 14, 16, and 18 may have 1,096 inputs and 1,096 outputs. The present invention allows any of the 1,096 inputs to digital cross-connect system 12 to be routed to any of the 1,096 outputs for digital cross- connect system 14, 16, or 18.

In addition, this routing may be accomplished without forming connections between the network interfaces of digital cross-connect systems 14, 16, or 18. For example, to connect an input to digital cross-connect system 12 to an output of digital cross- connect system 18 in a conventional system, it may be necessary to connect a network interface output of digital cross-connect system 12 to a network interface input of digital cross-connect system 14, and to further connect a network interface output of digital cross-connect system 14 to a network interface input of digital cross-connect system 16, and to further connect a network interface output of digital cross- connect system 16 to a network interface input of digital cross-connect system 18. The present invention avoids these digital cross-connect system network interface connections, and connects an input to digital cross-connect system 12 to an output of digital cross-connect system 18 through either counterclockwise data transmission medium ring 20 or clockwise data transmission medium ring 22.

FIGURE lb is an exemplary block diagram of a non- blocking PCM network 23 that includes three "A" plane data transmission ring interfaces 24, 26, and 28 at each of digital cross-connect systems 12, 14, 16, and 18. Data transmission ring interfaces 24, 26, and 28 are coupled via data transmission medium ring 22a, which comprises three separate data transmission paths, as shown. In general, X data transmission ring interfaces may be used, where X is an integer equal to the number of digital cross-connect systems minus 1. The data transmission capacity over data transmission ring interfaces 24, 26, and 28 is approximately three times the data transmission capacity of data transmission medium ring 22a. PCM network 23 also includes redundant "B" plane transmission rings (not explicitly shown) that perform in a manner similar to the "A" plane rings shown, with respect to data transmission medium 22. Non-blocking PCM network 23 operates in a manner similar to blocking PCM network 10, with the modifications described below.

In operation, digital cross-connect systems 12, 14, 16, and 18 route telecommunications traffic locally or to other remote digital cross-connect systems. For example, digital cross connect system 12 routes traffic to remote digital cross connect system 18 over ring 24, to remote digital cross connect system 16 over ring 26, and to remote digital cross connect system 14 over ring 28.

At each local digital cross connect system, telecommunications data received from the other remote digital cross connect systems at rings 24, 26, and 28 is always retransmitted to the other remote digital cross systems and is available at the local digital cross connect system. Each ring is capable of receiving and processing telecommunications data equivalent to the M network interface input ports of any one of the digital cross connect systems of PCM network 23.

For example, the telecommunications traffic routed to digital cross connect system 18 from digital cross connect system 12 over ring 28 includes telecommunications data received at digital cross connect system 12 over ring 26 from digital cross connect system 14. Likewise, the telecommunications traffic routed to digital cross connect system 18 from digital cross connect system 12 over ring 28 includes telecommunications data received at digital cross connect system 14 over ring 24 from digital cross connect system 16.

In this manner, local telecommunications data from digital cross connect system 16 is transmitted to digital cross connect system 14 over ring 24 of digital cross connect system 14. Furthermore, local telecommunications data from digital cross connect system 16 is transmitted to digital cross connect system 12 over ring 26 of digital cross connect system 12, and local telecommunications data from digital cross connect system 16 is transmitted to digital cross connect system 18 over ring 28 of digital cross connect system 18.

Rings 24, 26, and 28 thus prevent blocking from occurring in PCM network 23. All of the data received at the M network interface input ports of digital cross connect system 12 may be transmitted to digital cross connect system 18 without preventing the transfer of data from digital cross connect system 14 to digital cross connect system 16. FIGURE 2 shows a block diagram 30 of digital cross-connect matrix connections for one plane of digital cross-connect systems 12, 14, 16, and 18 for use in PCM network 10, as described below. Block diagram 30 may also be applied in PCM network 23 if insert fabric 34 is omitted, as noted in the description of PCM network 10 below.

As previously noted, in a digital cross-connect system such as that taught by Read, multiple redundant planes may be used to increase system reliability. Digital cross-connect plane 30 includes a ring interface 32 which couples to counterclockwise data transmission medium ring 20 and receives digitally encoded PCM data from counterclockwise data transmission medium ring 20. Alternately, ring interface 32 may couple to clockwise data transmission medium ring 22.

Ring interface 32 is also coupled to an administration system 45, a drop fabric 38 and an insert fabric 34. Drop fabric 38 is also coupled to administration system 45 and to a local fabric 40. Local fabric 40 is coupled to local interfaces 42 and 46, administration system 45, and a bridge circuit 47. Local interfaces 42 and 46 are coupled to unit shelves 44 and administration system 45. Insert fabric 34 also couples to administration unit 45 and ring interface 36, which transmits telecommunications data over counterclockwise data transmission medium ring 20 to other digital cross-connect matrices (not explicitly shown) .

Ring interface 32 is a telecommunications system that receives digitally encoded, pulse code modulated telecommunications data from counterclockwise data transmission medium ring 20. Ring interface 32 may alternately receive data from other suitable data transmission media, such as clockwise data transmission medium ring 22. Ring interface 32 transmits telecommunications data to local fabric 40 through drop fabric 38. Ring interface also transmits telecommunications data to other digital cross-connect systems (not explicitly shown) by transmitting the telecommunications data through insert fabric 34 to ring interface 36 and counterclockwise data transmission medium ring 20.

Drop fabric 38 is a telecommunications system that receives telecommunications data from ring interface 32 and transmits the telecommunications data to local fabric 40. Drop fabric 38 may comprise a number of digital telecommunications switches, each having M inputs and N outputs, wherein each telecommunications switch can connect any of M inputs to any of N outputs. Drop fabric 38 may further comprise time-slot interchange random access memory coupled to a time division multiplex data bus, and may be operable to store digitally-encoded telecommunications data on the time-slot interchange random access memory, to retrieve digitally-encoded telecommunications data from the time-slot interchange random access memory, and to encode data into a predetermined time slot of the time division multiplex data bus.

Local fabric 40 is a digital cross-connect system switching matrix comprising M input ports, N output ports, and circuitry operable to couple any of the M inputs to any of the N outputs, where M and N are integers. Local fabric 40 may receive telecommunications data from both drop fabric 38 and local interface 46. Local fabric 40 transmits the telecommunications data received at the M inputs from local interface 46 and drop fabric 38 to local interface 42, which are coupled to the N outputs of local fabric 40. Local fabric 40 may also be coupled to administration system 45, and may receive switching control and timing data from administration system 45. Local fabric 40 may further comprise time-slot interchange random access memory coupled to a time division multiplex bus, and may be operable to store digitally-encoded telecommunications data on the time- slot interchange random access memory. Local fabric 40 may be further operable to retrieve digitally- encoded telecommunications data from the time-slot interchange random access memory, and to encode data into a predetermined time slot of the time division multiplex data bus. Local fabric 40 is also operable to transmit data to and receive data from bridge circuit 47 in order to perform additional functions such as conference calling. For example, data received from three outputs of local fabric 40 may be switched back through local fabric 40 via bridge circuit 47 after three conference outputs have been created. In this manner, conference calling functions may be performed. Local interface 42 and local interface 46 are coupled to local fabric 40, unit shelves 44, and administration system 45. Local interface 42 is coupled to the output connections of local fabric 40, and local interface 46 is coupled to the input connections of local fabric 40.

Unit shelves 44 couple to local interfaces 42 and 46 and administration system 45, and are digital cross-connect system network interfaces. Telecommunications media carrying telecommunications data from the external telecommunications network (not explicitly shown) are coupled to unit shelves 44.

Administration system 45 couples to local interfaces 42 and 46, local fabric 40, unit shelves 44, ring interfaces 32 and 36, drop fabric 38, and insert fabric 34, and is operable to coordinate the routing of telecommunications data received from external telecommunications media at unit shelves 44 and ring interface 32. Administration system 45 may receive a distributed database that contains data on the status of components within PCM network 10. The database for PCM network 10 may be controlled by a publish and subscribe method, a token ring method, or other suitable methods. Administration system 45 may contain other suitable administration and controls components, such as those that may be necessary to communicate with a centralized administration unit. Insert fabric 34 couples to ring interface 32, local interface 46, administration unit 45, and ring interface 36. Insert fabric 34 receives telecommunications data from ring interface 32 for transmission to ring interface 36. In addition, insert fabric 34 receives telecommunications data from local interface 46 and switches the telecommunications data to counterclockwise data transmission medium ring 20, or other suitable data transmission media interface.

Insert fabric 34 may comprise time-slot interchange random access memory coupled to a time division multiplex bus, and may be operable to store digitally-encoded telecommunications data on the ti e- slot interchange random access memory, to retrieve digitally-encoded telecommunications data from the time-slot interchange random access memory, and to encode data into a predetermined time slot of the time division multiplex data bus. Ring interface 36 is a telecommunications system that couples to insert fabric 34. Ring interface 36 receives digitally-encoded PCM data from insert fabric 34 and transmits the telecommunications traffic over counterclockwise data transmission medium ring 20 to other digital cross-connect systems. As previously noted in regards to ring interface 32, ring interface 36 may also couple to other appropriate data transmission media.

Bridge circuit 47 couples to local fabric 40 and is operable to receive data from and transmit data to local fabric 40. Bridge circuit 47 performs additional functions on the data received from local fabric 40, such as creating conference call outputs. For example, bridge circuit 47 may perform signal processing on multiple data streams to create a conference call outputs. In operation, digital cross-connect plane 30 receives a plurality of channels of telecommunications traffic via counterclockwise data transmission medium ring 20. Digital cross-connect plane 30 also receives local telecommunications traffic through unit shelves 46. Telecommunications traffic through counterclockwise data transmission medium ring 20 may be addressed to other remote digital cross-connect systems by directing it to insert fabric 34 and ring interface 36. Otherwise, telecommunications traffic from counterclockwise data transmission medium ring 20 that is received at ring interface 32 is directed to drop fabric 38 for switching to local interface 42.

In addition to this telecommunications traffic from other remote digital cross-connect systems, local telecommunications traffic from connections made via unit shelves 44 is also switched through local fabric 40. Local fabric 40, local interfaces 46, and unit shelves 44 receive switching connection instructions from administration system 45. As previously noted, a central administration unit may also be used to control switch connections for digital cross-connect plane 30. Local fabric 40, drop fabric 38, and insert fabric 34 then make appropriate connections between telecommunications traffic channels from local interface 46 and ring interface 32 to local interface 42 and ring interface 36. For example, telecommunications traffic may be routed from a remote digital cross-connect system through counterclockwise data transmission medium ring 20 to ring interface 32 for connection to an output at local interface 42. This telecommunications traffic is routed to drop fabric 38 and local fabric 40. Local fabric 40 receives switching commands from administration system 45, and makes the connection between drop fabric 38 and local interface 42. Likewise, the telecommunications traffic received from a remote digital cross-connect system via counterclockwise data transmission medium ring 20 may not require switching through local fabric 40. In this case, the telecommunications traffic is instead routed to insert fabric 34 and ring interface 36 for retransmission to another remote digital cross-connect system. From ring interface 36, the telecommunications traffic is reinserted into counterclockwise data transmission medium ring 20. In addition, local telecommunications traffic may be routed from local fabric 40 onto counterclockwise data transmission medium ring 20 for transmission to a remote digital cross-connect system. For example, telecommunications data may be transmitted from local interface 46 to insert fabric 34. From insert fabric 34, the telecommunications data is transmitted to ring interface 36 and counterclockwise data transmission medium ring 20. Destination information for the telecommunications channel may be encoded into the telecommunications channel, or may be transmitted to the administration system of the remote digital cross- connect systems over a dedicated data transmission medium. For example, the switching connections for each digital cross-connect system of PCM network 10 may be maintained in a database that is duplicated in administration system 45 of each digital cross-connect system in PCM network 10.

One skilled in the art will recognize that modifications may be made to the digital cross-connect system of FIGURE 2 without departing from the spirit or scope of the present invention. For example, unit shelves 44 may perform the functions of local interfaces 42 and 46, such that unit shelves 44 couple directly to local fabric 40. Telecommunications traffic being routed through counterclockwise data transmission medium ring 20 may be channeled through drop fabric 38 directly to insert fabric 34, instead of from ring interface 32 to insert fabric 34.

Remote sources may include telecommunications traffic transmitted over counterclockwise data transmission medium ring 20 or clockwise data transmission medium ring 22. Local sources may include hardwired connections with copper or fiber optic cable. In particular, "local" and "remote" may apply interchangeably to any particular digital cross- connect system in relation to a second digital cross- connect system.

For example, a connection may be formed from a first digital cross-connect system to a second digital cross-connect system through the ring interface of a third digital cross-connect system. The second and third digital cross-connect systems are "remote" from the "local" reference frame of the first digital cross-connect. Likewise, the first and third digital cross-connects are "remote" from the "local" reference frame of the second digital cross-connect system, and the first and second digital cross-connect systems are "remote" from the "local" reference frame of the third digital cross-connect system.

In the example above, from the frame of reference of the first digital cross-connect system, a signal received at a local input port carrying telecommunications data is being transmitted to a first remote digital cross-connect system for subsequent retransmission to an output port of a second remote digital cross-connect system. From the frame of reference of the second digital cross-connect system, a signal carrying telecommunications data is being transmitted from an input port of a first remote digital cross-connect system through a second remote digital cross-connect system to a local output port. From the frame of reference of the third digital cross-connect system, a signal carrying telecommunications data is being transmitted from an input port of a first remote digital cross-connect system to an output port of a second remote digital cross-connect system.

In PCM network 23 shown in FIGURE lb, insert fabric 34 would not be required, because stages 24, 26, and 28 comprise individual data transmission paths similar to counterclockwise data transmission medium ring 20 and clockwise data transmission medium ring 22. Thus, data is transmitted to the local digital cross connect system and is repeated on to the next remote digital cross connect system, except at ring 28, where the data is not repeated to the next remote digital cross-connect system.

For example, ring 28 of digital cross connect system 12 comprises a ring interface 32 that is not coupled to an insert fabric 34 of digital cross connect system 12, and that couples to ring interface 32 of ring 26 of digital cross connect system 14, to ring interface 32 of ring 24 of digital cross connect system 16, and to ring interface 36 of digital cross connect system 18 over clockwise data transmission ring 22a.

Ring interface 32 of ring 26 of digital cross connect system 12 couples to ring interface 32 of ring 28 of digital cross connect system 18, to ring interface 32 of ring 24 of digital cross connect system 14, and to ring interface 36 of digital cross connect system 16 via clockwise data transmission medium ring 22a.

Ring interface 32 of ring 24 of digital cross connect system 12 couples to ring interface 32 of ring 26 of digital cross connect system 18, to ring interface 32 of ring 28 of digital cross connect system 16, and to ring interface 36 of digital cross connect system 14 via clockwise data transmission medium ring 22a.

Local interface 46 of digital cross connect system 12 directly couples to ring interface 36. Ring interface 36 of digital cross connect system 12 couples to ring interface 32 of ring 24 of digital cross connect system 18, to ring interface 32 of ring 26 of digital cross connect system 16, and to ring interface 32 of ring 28 of digital cross connect system 14 via clockwise data transmission medium ring 22a.

The connections described above allow data to be transmitted over PCM network 23 of FIGURE lb without the possibility of blocking, because each clockwise data transmission medium ring 22a is capable of carrying the total data traffic from any of digital cross connect systems 12, 14, 16, and 18. For example, if digital cross connect system 12 transmits all of its output data to the input ports of digital cross connect system 16, digital cross connect systems 14, 16, and 18 are not prevented from also transmitting data. Each digital cross connect system also comprises similar connections to counterclockwise data transmission medium rings 20a.

FIGURE 3 is a detailed block diagram of one plane of a digital cross-connect system 50, in accordance with the teachings of the present invention. Digital cross-connect system 50 is similar to digital cross- connect plane 30, but contains additional detail. Digital cross connect system 50 may be used in PCM network 10 of FIGURE la or may alternatively be used in PCM network 23 of FIGURE lb with the modifications described below. Digital cross-connect system 50 includes digital matrix interfaces 52 and digital matrix multiplexer/ demultiplexer cards 54. Digital matrix interfaces 52 and digital matrix multiplexer/demultiplexers 54 receive telecommunications traffic from remote and local sources, respectively.

Digital matrix cards 58 and 60 are telecommunications system components. Digital matrix card 58 is coupled to digital matrix interface 52 and digital matrix card 62. Digital matrix card 60 is coupled to digital matrix interface 52, digital matrix multiplexer/demultiplexer 54, and outbound digital matrix interface 56. Digital matrix card 62 is coupled to digital matrix multiplexer/demultiplexer 54 and digital matrix bridge 53. Digital matrix cards 58, 60, and 62 are time division multiplex switches comprising time slot interchange random access memory and time division multiplex buses, and controllably encode digital data onto the time division multiplex bus. Digital matrix cards 58, 60, and 62 may comprise the same component such as shown in FIGURE 3, or may comprise different components that are modified to perform specialized tasks. Digital matrix cards 58 and 62 share a time division multiplex bus, and controllably encode data onto the common time division multiplex bus.

Digital matrix multiplexer/demultiplexer cards 54 and outbound digital matrix interfaces 56 are telecommunications system components that are coupled to the time division multiplex buses of digital matrix cards 62 and 60, respectively. Digital matrix multiplexer/demultiplexer cards 54 are used to combine multiple lower frequency PCM data streams into a single high frequency PCM data stream for connection to the inputs of digital matrix cards 60 and 62, and to separate the lower frequency PCM data streams from the single high frequency PCM data stream received from the output connections of digital matrix cards 62. Outbound digital matrix interfaces 56 are similar to digital matrix interfaces 52, but are used to combine telecommunications channels from digital cross-connect system 50 for transmission to an external media, such as counterclockwise data transmission medium ring 20 or clockwise data transmission medium ring 22.

Digital matrix bridge cards 53 are telecommunications system components that couple to digital matrix cards 62, and which are operable to receive data from and transmit data to digital matrix cards 62. Digital matrix bridge cards 53 controllably receive, store, process, and transmit data to provide additional telecommunications services, such as conferencing. For example, digital matrix bridge cards 53 may receive a plurality of separate channels of data from digital matrix cards 62, create conference call outputs, and transmit the conference call outputs back to digital matrix cards 62. In operation, remote and local telecommunications data are received at digital matrix interfaces 52 and digital matrix multiplexer/demultiplexer cards 54, respectively. In system 10, remote telecommunications data received at digital matrix interfaces 52 that is routed to other digital cross-connect systems is transferred to digital matrix cards 60 for subsequent switching and transmission through outbound digital matrix interfaces 56 to an external data transmission media, such as counterclockwise data transmission medium ring 20 or clockwise data transmission medium ring 22. The remote telecommunications data is also transmitted to digital matrix cards 58. Likewise, local telecommunications traffic from digital matrix multiplexer/demultiplexer cards 54 is also routed to digital matrix cards 60 and 62. Digital matrix cards 62 are operable to store and switch digitally encoded data received from digital matrix multiplexer/demultiplexer cards 54 onto the time division multiplex buses provided to digital matrix multiplexer 54. Local telecommunications data that is to be provided to a remote cross-connect is provided to digital matrix cards 60 for subsequent switching and transmission through outbound digital matrix interface 56 to an external data transmission media, such as counterclockwise data transmission medium ring 20 or clockwise data transmission medium ring 22.

Digital matrix cards 58 and 62 are operable to switch the digitally-encoded telecommunications data received from digital matrix interfaces 52 and digital matrix multiplexer/demultiplexer cards onto a common time division multiplex bus, in accordance with switching data received from an administration system such as administration system 45 of FIGURE 2. Telecommunications traffic routed to digital matrix multiplexer/demultiplexer cards 54 is transmitted over local connections (not explicitly shown) to unit shelves that output the telecommunications traffic on network interfaces.

Alternatively, digital cross-connect system 50 may be used in network such as PCM network 23 of FIGURE lb when the following modifications are made. As noted with regard to FIGURE 2, digital matrix cards 60 are not required when additional telecommunications media rings are included, such as rings 24, 26, and 28 of FIGURE lb. Accordingly, digital matrix multiplexer/demultiplexer cards 54 couple directly to outbound digital matrix interfaces 56. Likewise, when digital cross-connect system 50 is used in PCM network 23, connections "a" between digital matrix interfaces 52 and digital matrix cards 60 are not present. Telecommunications data received over clockwise data transmission medium ring 22a or other similar telecommunications media are transmitted through repeaters to other digital cross connect systems, as previously described with respect to digital cross-connect plane 30 of FIGURE 2.

FIGURE 4 is a schematic diagram of a digital matrix interface card 52 embodying concepts of the present invention. An external data transmission medium, such as counterclockwise data transmission medium ring 20, couples to optical to electric converter 72. Optical to electrical converter 72 converts the telecommunications data stream received from counterclockwise data transmission medium ring 20 from light signals to electrical signals, and transmits the electrical signals to serial to parallel converter 78 and, when used in PCM network 23, to electrical to optical converter 74. Optical to electrical converter 72 receives an optical signal with digitally encoded data and converts the signal into an electrical signal with digitally encoded data. Optical to electric converter 72 may perform the conversion by decoding the data in the optical signal and encoding the data into an electrical signal. In PCM network 23, electrical to optical converter 74 receives remote telecommunications traffic signals from optical to electrical converter 72. This remote telecommunications traffic is converted from electrical to optical for transmission to another digital cross-connect system via clockwise data transmission medium ring 22a or other suitable external data transmission media.

Serial to parallel converter 78 may receive digitally-encoded PCM telecommunications data from optical to electrical converter 72 and convert it to digitally encoded PCM data transmitted in 16 bit words at 64 MHZ frequency. This digitally encoded data is received at demultiplexer 80. Demultiplexer 80 splits the parallel 16 bit word, 64 MHZ telecommunications data streams into two 16 bit word, 32 MHZ telecommunications data streams. Demultiplexer 80 then transmits the parallel 32 MHZ telecommunications data streams to two elastic store units 84 and 84'. Path ID monitors 82 and 82' monitor the 16 bit, 32 MHZ data being transmitted from demultiplexer 80 to elastic store units 84 and 84'. Elastic store units 84 and 84' store the 16 bit, 32 MHZ data that comprises telecommunications data and then retransmit the data after the telecommunications data is synchronized with local traffic.

The telecommunications data is then transmitted from elastic store units 84 and 84' to alignment units 86 and 86'. The telecommunications data is also transmitted from elastic store units 84 and 84' to a redundant mate digital matrix interface 52 of digital cross-connect system 50. This data from redundant mate digital matrix interface 52 is shown in FIGURE 4 as being received at parity monitor 88 and 88'.

Parity monitors 88 and 88' receive telecommunications data from the a redundant digital matrix interface 52 and monitor the parity of the digitally encoded data. Path ID is also monitored by path ID monitors 82 and 82'. This duplicated telecommunications data channel couples to multiplexers 90 and 90'. Multiplexers 90 and 90' receive the telecommunications data from alignment units 86 and 86' and from parity monitors 88 and 88' and select the data to create a single TDM data bus having 16 bit words and a speed of 32 MHZ. Time slot interchange ("TSI") RAMs 92 and 92' control the multiplexing operation. The multiplexed telecommunications data is transmitted to driver and parity monitors 98 and 98' while being monitored for path ID by path ID monitor 82 and 82'. In addition, even parity is inserted into telecommunications channel switched from multiplexers 90 and 90' to driver and parity monitors 98 and 98'.

In operation, telecommunications data received from clockwise data transmission medium ring 22a at optical to electrical converter 72 is transmitted to clockwise data transmission medium ring 22a in PCM network 23. The telecommunications data is then converted to two 16-bit 32MHz TDM buses by digital matrix interface 52 for connection to digital matrix cards 58. In contrast, the similar connection in PCM network 10 provides the telecommunications data to digital matrix cards 58 amd 60. Telecommunications traffic that is routed to digital cross-connect 50 for switching is split and processed by pairs of digital matrix interface cards 52. Prior to connection with digital matrix cards 58, the telecommunications traffic may be monitored for parity and path ID, and may be delayed to retime the telecommunications traffic to match local traffic time. Telecommunications traffic is then connected through driver and parity monitors 98 and 98' to digital matrix cards 58. In PCM network 10, telecommunications traffic is routed from demultiplexer 80 to digital matrix card 60 through a ring elastic store unit, path ID monitor and driver and parity monitors (not explicitly shown) . FIGURE 5 is an exemplary block diagram of digital matrix multiplexer/demultiplexer 54. Digital matrix multiplexer/demultiplexer 54 is used in a multiplexer capacity to connect local telecommunications traffic from unit shelves 44 to digital matrix cards 62, and also to digital matrix card 60 in PCM 10. In PCM 23, digital matrix multiplexer/demultiplexer 54 is used to connect local telecommunications traffic from unit shelves 44 to digital matrix cards 62 and also to outbound digital matrix interface 56. In addition, digital matrix multiplexer/demultiplexer 54 is used in a demultiplexer capacity to connect telecommunications traffic from digital matrix cards 62 to unit shelves 44 in both PCM 10 and 23.

Digital matrix multiplexer/demultiplexers 54 include input devices 102. Input devices 102 receive 16 bit, 5 MHZ, digitally encoded PCM data from unit controllers (not explicitly shown) located in unit shelves 44 of FIGURE 2, which are used to couple unit shelves 44 to digital cross-connect matrix 30. Path ID monitors 100 are used to provide fault isolation for cross-connect telecommunications data traffic, such as to determine source address information and routing through the cross-connect system.

Input devices 102 couple to cable equalization circuit 104. Cable equalization circuit 104 couples to multiplexer 106, which receives the six-16 bit, 5 MHZ, parallel PCM data from cable equalization circuit 104 and converts the telecommunications data into 32 MHZ, 16-bit digitally encoded PCM data. Cable equalization circuit 104 also introduces appropriate timing delays to compensate for cable length differences in the cabling that connects unit shelves 44 to digital matrix multiplexer/demultiplexers 54 FIGURE 3. Multiplexer 106 couples to parity monitor 88. In addition, path ID monitor 100 and even parity insertion unit 108 monitor and modify the telecommunications data.

Digital matrix multiplexer 54 receives 16-bit, 32 MHZ outbound PCM data after it has been switched from digital matrix cards 62 and transmits the data to elastic store unit 112. Path ID monitor 100 and parity monitor 88 monitor the path ID of each telecommunications data channel prior to transmission to elastic store unit 112. Elastic store unit 112 is used to control the delay of the data transmission time in order to synchronize data transmission with the local system data transmission rate.

Demultiplexer 114 receives the 16-bit 32 MHZ signal and demultiplexes it into six 16-bit, 5 MHZ signals. Parity monitor 111 and path ID monitor 100 monitor the demultiplexed signals for correct path ID and parity. The demultiplexed signals are transmitted to outbound PCM connections through output interfaces 116. Output interfaces 116 couple to unit controllers in unit shelves 44 of FIGURE 2.

In operation, digital matrix multiplexer/ demultiplexers 54 are used to multiplex two or more low speed telecommunications data streams into a single high-speed telecommunications data stream for switching through the digital cross-connect matrix, and to demultiplex the high speed telecommunications data signals that have been switched through the digital cross-connect matrix to lower speed telecommunications data channels for subsequent transmission through unit shelves 44 to the telecommunications network. Digital matrix multiplexer/demultiplexers 54 receive control data from administration system 45 and are operable to controllably multiplex and demultiplex the telecommunications data in response to the control data.

FIGURE 6 is an exemplary schematic diagram of digital matrix card 62 embodying concepts of the present invention. As previously mentioned, digital matrix cards 58, 60, and 62 may be identical, or may comprise different components that are modified to perform specialized tasks. Digital matrix cards 58 and 60 are identical to digital matrix card 62 with the modifications described below.

Digital matrix card 62 includes differential receivers 122, which are digital data transmission system components that receive N input signals and output N/2 signals. Differential receivers 122 are operable to transfer a signal carrying digitally encoded data from a two-conductor pair to a signal on a single conductor. Administration circuitry 124 couples to differential receivers 122 and processes the data signal to perform parity testing, frame alignment, and signaling collection. Differential receivers 122 also couple to elastic store units 128, which couple to time-slot interchange random access memories 126 (TSI RAMs) .

Elastic store units 128 are data buffers that are used to synchronize local telecommunications traffic with telecommunications traffic received from remote digital cross connect systems. For example, the transmission delay caused by the length of the telecommunications media between the local and remote digital cross connect systems may require local telecommunications data to be temporarily stored in order to synchronize that data with remote data. This function is performed by elastic store units 128.

Time slot interchange RAMs 126 are digital data transmission system components that are operable to store and retrieve digital data. Time slot interchange RAMs 126 are operable to function as a switch having M data inputs and N data outputs. For example, time slot interchange RAMs 126 may have a total of M input ports and N output ports, and may read data from the M input ports and write data to the N output ports.

Data is switched through time slot interchange RAMs 126 by controlling the time slot from which data is read for any given data output channel. Thus, any data written to time slot interchange RAMs 126 from the M input ports may be read from the N output ports. Time slot interchange RAMs 126 are further grouped into bridge row and column 130 and switching fabric 132.

In operation, digitally-encoded data is transmitted through differential receivers 122 to time slot interchange RAMs 126. The digitally-encoded data is stored by writing to time slot interchange RAMs 126, and is then encoded onto a time division multiplex bus at a predetermined time slot. The time- slot encoded data is transmitted to differential drivers 134 for external transmission. Data is switched through time slot interchange RAMs 126 by controlling the time slot that the data is encoded into.

When the digital matrix card of FIGURE 6 is applied to digital matrix cards 58 and 60, elastic store units 128 and bridge row and column 130 are not included in the circuit. Digital matrix cards 58 and 60 do not perform any of the bridging functions described above. The buffering function for digital matrix bridge cards 58 and 60 is performed by digital matrix interface cards 52.

FIGURE 7 is an exemplary schematic diagram of a outbound digital matrix interface 56 embodying concepts of the present invention. Digital matrix interface/output card 140 receives digitally-encoded telecommunications data in the form of 16-bit words at 32 MHZ at parity monitors 88 from digital matrix cards 60 in PCM network 10 or from digital matrix multiplexers/demultiplexers 54 in PCM network 23. Path ID monitor 82 monitors administration and control data that may be encoded into predetermined data locations within the data format. The digitally encoded telecommunications data is multiplexed by multiplexer 142 into a 16 bit word, 64 MHZ signal. Parallel to serial converter 144 converts the parallel telecommunications data transmitted from multiplexer 142 into serial telecommunications data for input to electrical to optical converter 146. Electrical to optical converter 146 transmits the digitally encoded serial telecommunications data over counterclockwise data transmission medium ring 20 to other digital cross-connect systems that comprise PCM network 10, or over counterclockwise data transmission medium ring 20a to a remote digital cross connect system in PCM network 23.

FIGURE 8 is an exemplary flow chart 160 for a method for interconnecting two or more digital cross- connect systems into a single PCM network embodying concepts of the present invention. At step 162, telecommunications data is received at a digital cross-connect system. This telecommunications data may comprise destination data, routing data, and the telecommunications data that is being transmitted between two telecommunications system interfaces. In addition, the digital cross-connect system may comprise two redundant parallel planes.

At step 164, it is determined whether the telecommunications data is a local signal for switching from an input port of the switching matrix of the local digital cross-connect system to an output port of the local digital cross-connect system, such as by receiving address or path ID data from administration system 45. If the telecommunications data is a local signal, the method proceeds to step 166. If the telecommunications data is not a local signal, it may be a remote signal for switching from an input port of the local digital cross-connect system to an output port of a remote digital cross- connect system in PCM network 10. If the telecommunications data is a remote signal, the method proceeds to step 170.

At step 166, the telecommunications data is routed through the switching matrix of the local digital cross-connect system by forming a connection between the input port which is coupled to the source of the telecommunications data and the output port that couples to the destination of the telecommunications data. Once the connection is made between the source and the destination for the telecommunications data, the method proceeds to step 168 and terminates.

At step 170, the telecommunications data is routed to at least two counter-rotating rings that comprise at least two data transmission media that couple all digital cross-connect systems that comprise the single PCM network 10. For example, the single PCM network may include four digital cross-connect systems. These four digital cross-connect systems may be interconnected by two counter-rotating rings of data transmission media, as shown in FIGURE la.

Furthermore, each digital cross-connect system may comprise two redundant parallel planes as taught in Read, such that two independent paths may be formed to connect the input port to the output port for the purpose of transmitting the telecommunications data. If each digital cross-connect system comprises two redundant parallel planes, then the first redundant parallel plane may be coupled to the first counter- rotating data transmission medium ring, and the second redundant parallel plane may be coupled to the second counter-rotating data transmission medium ring. The step of routing the telecommunications data may include converting electrical signals carrying the encoded data into light signals carrying the encoded data. This electrical to optical conversion is accomplished with an electrical to optical converter that may be contained within the ring interface that couples the digital cross-connect system to the data transmission media.

At step 172, the telecommunications data are received at the remote digital cross-connect systems that are coupled to the counter-rotating data transmission media rings. The telecommunications data may be converted from optical to electrical signals at this step. The remote digital cross-connect system then proceeds to step 164, where the telecommunications data is processed in a manner that is similar to processing of local signals at the remote. If the telecommunications data that has been transmitted to the remote digital cross-connect system is to be routed to an output port of the remote digital cross-connect system, the method proceeds to step 166 and the telecommunications data is routed to the appropriate output port. Otherwise, in PCM network 10 the method proceeds to step 170, and the remote digital cross-connect system proceeds to transmit the telecommunications data to the next remote digital cross-connect system on the counter- rotating data transmission media rings.

In operation, the method shown in FIGURE 8 would function as follows when applied to the system shown in FIGURE la. Telecommunications data would be received at an input port of one of the digital cross- connect systems shown in FIGURE la, such as digital cross-connect system 12. This step corresponds to method step 162. The method would then determine at step 164 whether the telecommunications data should be routed to an output port of digital cross-connect system 12, or whether the telecommunications data needs to be routed to an output port of one of digital cross-connect systems 14, 16, and 18.

If the telecommunications data is local, i.e. is to be routed to an output port of digital cross- connect system 12, then the method proceeds to step 166. Otherwise, the method proceeds to step 170, and the telecommunications data is transmitted to the other digital cross-connect systems over counter- rotating data transmission media rings 20 and 22 in PCM network 10.

In PCM network 10, the method proceeds until the telecommunications data has been routed to the digital cross-connect system having the appropriate output port, such as digital cross-connect system 18. Thus, the telecommunications data will be transmitted over counterclockwise data transmission media ring 20 to digital cross-connect system 14, 16 and 18, and over clockwise data transmission media ring 22 to digital cross-connect system 18. If each digital cross- connect system is comprised of parallel planes, as taught in Read, then counterclockwise data transmission media ring 20 may be coupled to the first parallel plane of each digital cross-connect system, and clockwise data transmission media ring 22 may be coupled to the second parallel plane of each digital cross-connect system. In this manner, the transmission of data between any two digital cross-connect systems that comprise PCM network 10 of FIGURE 1 will not be prevented in the event of a physical break or similar disruption at one point around the ring formed by counter-rotating data transmission media rings 20 and 22. For example, if a physical break occurs in the data transmission media that comprises counterclockwise data transmission media ring 20 and clockwise data transmission media ring 22 between digital cross- connect system 12 and digital cross-connect system 14, an alternate path between digital cross-connect system 12 and digital cross-connect system 14 will remain via digital cross-connect systems 18 and 16.

In summary, a network, system, and method has been presented that allows multiple digital cross- connect systems to be connected into a single PCM network. The digital cross-connect systems are coupled via at least two counter-rotating fiber optic conductors, such that a signal carrying telecommunications data that is connected to an input port of any digital cross-connect system may be coupled to the output port of any other digital cross- connect system that comprises the PCM network.

The present invention provides many technical advantages. One important technical advantage of the present invention is that two or more digital cross- connect systems may be interconnected to form a single PCM network without reconfiguring the digital cross- connect switch input port and output port connections. Another important technical advantage of the present invention is that it provides a method for connecting telecommunication circuits through two or more digital cross-connect systems without requiring switching through each digital cross-connect system's network interface ports. Therefore, the present method does not consume revenue producing network interfaces when telecommunications data is routed through a digital cross-connect system to a network interface at another digital cross-connect system

Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A telecommunications network comprising: a data transmission medium; and at least two digital cross-connect systems each having M network interface input ports and N network interface output ports, where M and N are integers greater than 0, the digital cross-connect systems being interconnected by the data transmission medium and operable to connect any one of M network interface input ports of any digital cross-connect system to any one of N network interface output ports of any other digital cross-connect system.

2. The telecommunications network of claim 1 wherein the data transmission medium comprises fiber optic conductors.

3. The telecommunications network of Claim 1 wherein each digital cross-connect system further comprises: a switching matrix having M network interface input ports and N network interface output ports, the switching matrix operable to connect any of the M network interface input ports to any of the N network interface output ports; and a ring interface coupled to the switching matrix and the data transmission medium, the ring interface operable to transmit telecommunications data from the data transmission medium to the switching matrix, the ring interface further operable to transmit telecommunications data from the switching matrix to the data transmission medium.

4. The telecommunications network of Claim 3 wherein the switching matrix comprises a digital matrix card.

5. The telecommunications network of Claim 3 wherein the ring interface comprises a digital matrix interface card.

6. The telecommunications network of Claim 3 wherein each digital cross-connect system further comprises at least two redundant parallel planes, and the data transmission medium further comprises two redundant data transmission media.

7. The telecommunications network of Claim 3 further comprising a bridge circuit coupled to the switching matrix, the bridge circuit operable to transmit data from the local fabric output ports to the local fabric input ports.

8. The telecommunications network of Claim 1 wherein each digital cross-connect system further comprises : a switching matrix having M + K input ports and N + L output ports, the switching matrix operable to connect any of the M + K input ports to any of the N

+ L output ports, where K and L are integers greater than zero; a first ring interface having K output ports, the K output ports of the first ring interface coupled to K input ports of the switching matrix, the first ring interface further coupled to the data transmission medium, the first ring interface operable to transmit telecommunications data from the data transmission medium to the switching matrix; and a second ring interface having L input ports, the L input ports of the second ring interface coupled to the L output ports of the switching matrix, the second ring interface further coupled to the data transmission medium, the second ring interface operable to receive telecommunications data from the switching matrix and to transmit the telecommunications data over the data transmission medium.

9. The telecommunications network of Claim 8 wherein each digital cross-connect system further comprises at least two redundant parallel planes, and each data transmission medium further comprises two redundant data transmission media.

10. The telecommunications network of Claim 8 further comprising: the telecommunications medium further comprising X telecommunications media, wherein X is an integer greater than 0; each digital cross-connect system further comprising X first ring interfaces and X second ring interfaces; the X first ring interfaces coupled to the X telecommunications media; and the X second ring interfaces coupled to the X telecommunications media.

11. The telecommunications network of Claim 10 wherein X is equal to the number of digital cross- connect systems minus one.

12. A system for interconnecting two or more digital cross-connect systems comprising: a data transmission medium coupled to a data transmission medium interface of each digital cross- connect; and each digital cross-connect is operable to transmit data to any other digital cross-connect over the data transmission medium so as to connect any one of a plurality of network interface inputs of any digital cross-connect system to any one of a plurality of network interface outputs of any other digital cross connect system.

13. The system of Claim 12 wherein each digital cross-connect further comprises: a switching matrix having M inputs and N outputs, wherein N and M are integers greater than 0; and a ring interface coupled to the switching matrix and the data transmission medium, the ring interface operable to transfer telecommunications data from the data transmission medium to the switching matrix, the ring interface further operable to transfer telecommunications data to the data transmission medium from the switching matrix.

14. The system of Claim 13 wherein each digital cross-connect system further comprises at least two parallel planes and the data transmission medium comprises at least two redundant data transmission media.

15. The system of Claim 12 wherein the ring interface further comprises a plurality of ring interfaces, and the data transmission medium further comprises a plurality of data transmission media.

16. The system of Claim 13 further comprising a bridge circuit operable to transmit data from the N outputs of the switching matrix to the M inputs of the switching matrix.

17. The system of Claim 12 wherein each digital cross-connect further comprises: a switching matrix; and a first ring interface coupled to the switching matrix and the data transmission medium, the first ring interface operable to transfer telecommunications data from the data transmission medium to the switching matrix; and a second ring interface coupled to the switching matrix and the data transmission medium, the second ring interface operable to transfer telecommunications data from the switching matrix to the data transmission medium.

18. The system of Claim 17 further comprising: a drop fabric coupled between the first ring interface and the switching matrix, the drop fabric operable to transfer telecommunications data from the ring interface to the switching matrix; and an insert fabric coupled to the first ring interface, the second ring interface, and the switching matrix, the insert fabric operable to transfer telecommunications data from the switching matrix to the second ring interface and to transfer telecommunications data from the first ring interface to the second ring interface.

19. The system of Claim 18 wherein the drop fabric comprises a digital matrix card.

20. The system of Claim 18 wherein the insert fabric comprises a digital matrix card.

21. A method for interconnecting two or more digital cross-connect systems comprising the steps of: receiving telecommunications data at a local digital cross-connect system; determining whether a destination for the telecommunications data is at the local digital cross- connect system or at a remote digital cross-connect system; routing the telecommunications data through a local switching matrix if the destination for the telecommunications data is at the local digital cross- connect system; and transmitting the telecommunications data over a data transmission medium if the destination is at the remote digital cross-connect system.

22. The method of Claim 21 further comprising the steps of: receiving the telecommunications data at a first remote digital cross-connect system from the data transmission medium; determining whether the destination for the telecommunications data is at the first remote digital cross-connect system or at a second remote digital cross-connect system; routing the telecommunications data through a local switching matrix if the destination for the telecommunications data is at the first remote digital cross-connect system; and transmitting the telecommunications data over the data transmission medium if the destination is at the second remote digital cross-connect system.

23. The method of Claim 21 wherein the step of transmitting further comprises the steps of: encoding the telecommunications data into an optical signal; and transmitting the optical signal over a fiber optic conductor.

24. The method of Claim 22 wherein the step of transmitting further comprises the steps of: encoding the telecommunications data into an optical signal; and transmitting the optical signal over a fiber optic conductor.