Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-11-12
2003-06-24
Chin, Wellington (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C379S093060
Reexamination Certificate
active
06584117
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to communication systems, and is particularly directed to a new and improved embedded operations channel (EOC)-based signalling mechanism, that is incorporatable within transceiver interface (U-BR1TE) components of an integrated services digital network (ISDN) telecommunication system, for effecting a relatively fast, warm start reactivation of a deactivated extended ISDN link between an ISDN switch and customer premises equipment.
BACKGROUND OF THE INVENTION
Integrated services digital network (ISDN) communication systems enable telecommunication service providers to supply multiple types of signalling channels from a central office over a signal local loop twisted pair to a network termination interface at a customer premises site. ISDN signalling channels, for example, typically include digital data and/or digitized voice (bearer B1/B2) channels, as well as a separate administrative (D) channel that conveys call control information.
FIG. 1
shows a reduced complexity example of a non-extended distance ISDN communication system, in which ISDN communications are provided over a local (two-wire metallic) loop
13
directly connecting a central office site (CO)
10
to a customer premises site
20
.
FIG. 2
diagrammatically illustrates a typical extended distance ISDN communication system, wherein ISDN connectivity between the CO site
10
and a remotely located customer premises site
20
is provided over an extended (PCM) communication link (such as a fiber optic link)
30
.
In each of these two ISDN networks, the central office site
10
includes a central office switch
11
(such as a 5ESS switch manufactured by AT&T), which contains a plurality of ISDN transceiver circuits (ISDN U-interface circuits), one of which is shown at
12
. For the non-extended distance ISDN system of
FIG. 1
, the ISDN U-interface circuit
12
terminates one end of a local loop (twisted tip/ring pair)
13
, a second end of which ported to a network termination interface (NT-1) circuit
21
serving customer premises equipment, such as ISDN data terminal equipment (DTE)
22
.
In the extended distance system of
FIG. 2
, a U-interface circuit
12
of the central office site
10
, located at a ‘west’ end of extended (PCM) communication link
30
, is coupled over the local loop
13
to what is termed in the telephone industry as a U Basic Rate-One Transmission Extension (U-BR1TE) transceiver card
14
(also referred to as a Basic Rate Interface Transmission Extension (U-BRITE) card).
A respective U-BR1TE (or U-BRITE) card contains an ISDN U-interface circuit and an associated PCM bus interface which are operative to transmit and receive standard 2B+D ISDN data traffic over a PCM digital data link, such as a T1=1.544 MB/s link, and to interface the ISDN signals via the local loop to and from loop termination equipment. Namely, the U-BR1TE card
14
at the ‘west’ end of the link
30
interfaces the local loop
13
with a digital data link
30
for PCM signalling transport to another U-BR1TE transceiver card
24
at an ‘east’ end of the link
30
, serving the customer premises equipment (CPE) site
20
. The ‘east’ U-BR1TE transceiver card
24
is coupled, in turn, over a local loop (twisted two-wire tip/ring pair)
23
to the network termination interface (NT-1) circuit
21
, to which customer premises ISDN data terminal equipment
22
is coupled.
A typical ISDN U-interface circuit is capable of operating in what is commonly referred to as a ‘warm’ start mode, which allows the loop to be deactivated and then, relatively quickly reactivated at a later time, by using an abbreviated training sequence that customarily requires up to 300 msec, rather than up to as many as fifteen seconds in what is commonly referred to as ‘cold start’ mode. Only the ISDN switch can command deactivation of the link, while either the ISDN switch or the customer premises NT-1 can initiate reactivation of a previously deactivated loop (by the transmission of a 10 kHz wake-up tone).
In order to initiate a warm start deactivation sequence, the ISDN switch
11
sets a specific ‘downstream only’ maintenance bit in an overhead channel to the NT-1 circuit
21
. While this procedure is straightforward forward in the non-extended network of
FIG. 1
, it becomes a problem in the extended network of
FIG. 2
, as there is no defined scheme to signal reactivation across an extended interface between the ISDN switch and the NT-1. To address this problem, Bellcore publication TR-NWT-000397 proposes waking up, or reactivating, an extended link by toggling the state of the ACT bit within the M4 out-of-band maintenance channel alternately between opposite logic levels.
In particular, the ACT bit is transmitted low for three sequential superframes, high for the next three superframes, and then low for the next three superframes. Upon detecting this ACT bit toggling sequence, the U-BR1TE card
24
at the receiving end of the extended link supplies the 10 Khz wake-up tone over the local loop
23
to the NT-1. A problem with this approach is the significant delay involved (nine superframes×twelve msec per superframe=108 msec of additional delay in bringing up both loops), which may cause layer two and layer three signaling errors.
SUMMARY OF THE INVENTION
In accordance with the present invention, this multiple superframe-based delay problem in reactivating an extended ISDN link is successfully addressed by means of a communication control software mechanism, which utilizes the embedded operations channel (EOC) to convey a relatively fast ‘wake-up the loop’ message (that consumes only six msec of delay) between U-BR1TE circuits terminating the extended distance loop. In response to such a ‘wake-up the loop’ message, the receiving U-BR1TE card proceeds to provide a 10 Khz wake-up tone to its associated termination equipment (either to the NT-1 in the case of a switch-sourced reactivation, or to the ISDN switch in the case of an NT-1 sourced wake-up request), thereby waking up the loop.
REFERENCES:
patent: 5260970 (1993-11-01), Henry et al.
patent: 5852630 (1998-12-01), Langberg et al.
patent: 5896390 (1999-04-01), Williams
patent: 5943404 (1999-08-01), Sansom et al.
Adtran Inc.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Chin Wellington
Pham Brenda
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