Multiplex communications – Fault recovery – Bypass an inoperative channel
Patent
1996-10-10
1999-10-26
Vu, Huy D.
Multiplex communications
Fault recovery
Bypass an inoperative channel
370244, H04J 314
Patent
active
059740272
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a telecommunications network including a channel switching protection arrangement and in particular relates to a way of identifying a channel, section, path or the like so that it can be switched remotely in an SDH (Synchronous Digital Hierarchy) network.
Conventionally in SDH the term "section" is associated with the physical links between adjacent nodes in a network, while the term "path" is associated with a communication link between a pair of nodes, wherever they are located in the network. Each section and path is uniquely identified in SDH by a so called section or path trace signal respectively which has in the past been used as a means of checking that a traffic signal arriving at a particular node is the correct one and for raising an alarm signal if it is not. As used within the specification the term "channel" will be used to describe either a path or a section, the important factor being that each channel, path or section connecting a pair of nodes is uniquely identified by means of a trace signal.
SDH, and the similar North American SONET (Synchronous Optical Network) system, provide a number of protection strategies including Multiplex Section and Path Protection. These strategies provide an adequate means for supporting a 1+1 or 1:1 architecture (i.e. those where one protection path or section serves one working path or section). However a 1:n architecture (i.e. where one protection path or section serves n working paths or sections) is of limited use in Multiplex Section Protection and is not provided for at all by Path Protection.
Multiplex Section Protection (MSP) provides a means of protecting the STM-N (Synchronous Transport Module)/STS-n (Synchronous Transport Signal) signal against channel-associated failures within the multiplex section. A protocol is supported by the K1/K2 bytes and as such provides for either linear protection switching between two adjacent sites or ring switching where the protection between two adjacent sites has also failed.
Path Protection provides a means of protecting the VC-n (Virtual Container)VT-n (Virtual Tributary) signal against channel associated failure within the higher-order/lower-order path respectively. A protocol has been proposed that will support a 1+1 or 1:1 switching only and in its present form could never support a 1:n architecture due to the vast amount of paths present at any one node and as such in the entire network.
SUMMARY OF THE INVENTION
One method of avoiding long delays in a bidirectional multiplex section--switched self healing ring transmission system is described in EP 0573211. The switching paths to be protected are distributed to ring node other than those immediately adjacent the failure. Each node if it has been communication traffic affected by the failure can bridge and switch to and from the protection paths.
The present invention provides, in one aspect, a telecommunications network of a type operating using Synchronous Digital Hierarchy (SDH) which comprises a plurality of interconnected nodes in which working channels are defined between respective pairs of nodes, and one common protection channel is provided to serve a plurality of working channels characterised by means for detecting a fault at a first node on a working channel traffic signals passing from a first node to a second node, means for switching that working channel on to the protection channel, the first node being operative to transmit a channel trace signal along with the traffic signals which serves to identify the respective channel, the second node being operative to monitor for the presence of a channel trace signal on a protection channel for which it is the terminating node and upon detection thereof to switch traffic signals associated with that trace signal on the protection channel into the said second node for connection to an onward destination.
The present invention makes use of the channel trace signal, (i.e. Section Trace JO--previously C1 in the Section Overhead) and Path Trace (
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A Novel Passive Protected SONET Bidirectional Self-Healing Ring Architecture, Tsong Ho Wu, et al., 8317 Journal of Lightwave Technology, Sep. 10, 1992, No. 9, New York, US.
Self-Healing Rings in a Synchronous Environment, Izaz Haque, et al., IEEE Lts, Nov. 1991, pp. 30-37.
GPT Limited
Vu Huy D.
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