Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-10-16
2001-05-08
Zimmerman, Mark (Department: 2671)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S463000, C370S400000
Reexamination Certificate
active
06229814
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to communication systems, in particular digital loop carrier (DLC) networks, and is directed to a new and improved line card installable in a single card slot of the backplane of a digital switch serving a central office. The multi-circuit line card of the invention is configured to emulate a plurality of digital switch line cards, respectively associated with a plurality of digital subscriber circuits served by the switch, and is operative to provide connectivity between such digital subscriber circuits and a digital carrier communication link to plural digital subscriber loop circuits of a remote terminal site.
BACKGROUND OF THE INVENTION
In order to extend digital service to customer premises equipment (CPE) served by a remote terminal (RT), telephone networks customarily employ a digital loop carrier (DLC) system, such as Ti carrier system for time division multiplexed data format (e.g., Bellcore standard TR-NWT-000397) diagrammatically illustrated in FIG.
1
. In this ‘universal’ type of DLC system, opposite ends of the digital carrier communication link (the T
1
link)
10
are coupled to a central office terminal (COT)
12
and a remote terminal (RT)
14
, respectively. For multiplexing and demultiplexing digital traffic conveyed over the T
1
carrier link
10
with digital subscriber loops (DSL)s
21
of an associated switch
20
(such as an AT&T 5ESS switch), the central office terminal
12
may contain a plurality of digital loop carrier circuits
13
, such as basic rate interface transmission extender cards, commonly referred to as BRITE cards or U-BRITE cards. Each BRITE card
13
is coupled over a respective DSL
21
to one of a plurality of line cards
23
of the switch
20
. In a complementary manner, the remote terminal
14
may contain a plurality of BRITE cards
15
, respectively associated with DSLs
16
serving respective CPEs.
For digital switch applications, the digital subscriber loops
21
between the switch
20
and the COT
12
become superfluous and may therefore be eliminated by terminating the carrier link to the remote terminal with the switch. For this purpose, two Bellcore ‘integrated’ digital loop carrier systems—TR-NTW-0008 and GR-CORE-303—have been proposed. The purpose of these systems is to reduce the cost per subscriber (by eliminating the subscriber loops between the switch and the COT), and to increase bandwidth efficiency by concentration at the carrier facilities.
However, each has its shortcomings. First of all, the TR-NTW-0008 system does not provide for deployment of ISDN signalling. Secondly, the GR-CORE-303 system, which does deploy ISDN, involves a substantial modification of the configuration of the switch, requiring a substantial capital investment, that is passed on to the subscriber in the form of higher costs (which become prohibitive in areas of low subscriber density).
SUMMARY OF THE INVENTION
In accordance with the present invention, this problem is solved by a new and improved line card that is installable in a digital switch serving a central office, and is operative to emulate or ‘mimic’ the functionality of each of a plurality of digital switch line card circuits, that are respectively associated with a plurality of digital subscriber circuits served by the switch. In the course of emulating these plural line cards, the multi-circuit line card configuration of the invention provides connectivity between each digital subscriber circuit and a digital carrier communication link to plural digital subscriber loop circuits of a remote terminal site. Because it is installable in an individual one of the backplane card slots of the switch, the multi-circuit line card of the invention provides a substantial decrease in hardware, and therefore reduces the cost associated with providing ISDN service to low subscriber density areas.
As will be described, the multi-circuit line card according to the present invention comprises a card processor-controlled digital switch backplane interface, that is made up of a plurality of backplane interface circuits—one for each (replaced) line card to be emulated. As the processor steps through or scans the backplane interface circuits, each circuit is operative to interface digital subscriber loop (DSL) signals (such as ISDN signals) and control signals with the respective signalling and control bus portions of the switch backplane.
For outgoing DSL signals from associated subscriber loops, a respective backplane interface circuit extracts the DSL data signals from the backplane and supplies a response to the switch over the backplane control bus. In the incoming direction, DSL signals for associated subscriber loops from the T
1
carrier link are controllably placed onto the backplane data bus.
To link DSL signals to and from the (T
1
) digital carrier link, each backplane interface circuit is coupled to a respective data format circuit of a data format interface. Each data format circuit formats DSL data in accordance with a prescribed time division multiplexed data format (such as the above-mentioned Bellcore standard TR-NWT-000397) for application to the digital carrier link by a digital carrier interface (multiplexer—demultiplexer). At the remote terminal, the respective ISDN subscriber channels transported by the carrier data stream are converted into plural ISDN subscriber loops for delivery to their associated CPE circuits. In the incoming direction from the T
1
link, each data format circuit extracts the DSL signals from the (TR 397) formatted data from the digital carrier interface and couples the DSL signals to an associated backplane interface circuit.
In order to create the appearance of the presence of a network or customer interface to tip and ring leads of a metallic test bus, the multi-circuit line card of the present invention further includes selectively connectable network and subscriber circuit-associated metallic link impedance simulation circuits. Each impedance simulation circuit may comprise a resistor-capacitor network, that is controllably configured by the card's control processor to provide a prescribed test bus termination impedance. The metallic link simulation circuits serve to replicate loop impedance signatures that would normally be presented by each replaced or phantom subscriber loop circuit between the switch and the central office terminal. This feature enables the multi-circuit line card of the invention to appear to the switch as a plurality of subscriber loops that had been extended through the conventional use of a universal digital loop carrier system containing central office terminal and remote terminal hardware.
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patent: 4852160 (1989-07-01), Kiko et al.
patent: 5202919 (1993-04-01), Kiko
patent: 5680391 (1997-10-01), Barron et al.
patent: 5940388 (1999-08-01), Nahar et al.
patent: 5943404 (1999-08-01), Sansom et al.
patent: 5999725 (1999-12-01), Barbier et al.
patent: 6018529 (2000-01-01), Toth
McMillian Lonnie S.
Sansom Michael Scott
Venters W. Stuart
Adtran Inc.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Santiago Enrique L
Zimmerman Mark
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