Northern Telecom Limited

Nortel Networks Corporation

Khalid Ahmad

Jan Medved

David Wright Martin

Yucheng Ye

A packet based telecommunication system, such as ATM, comprises a main data path and at least one bypass path, for bypassing a portion of the data path, the portion and the respective bypass defining a protection domain, the system comprising nodes for each of the domains, for monitoring respective domains and for issueing alarms in the form of packets, to other nodes downstream, with a domain identifier indicating the respective domain in which the alarm originated. At a given one of the nodes an alarm issued from a node upstream of the given node and a corresponding identifier, are detected. At the given node it is determined whether to trigger a rerouting of the data along one of the bypass paths which bypasses the domain monitored by the given node, on the basis of the detected domain identifier. Using the identifier, downstream nodes can determine more easily whether the alarm is caused by a domain which has a bypass path triggered by another node upstream. Thus the problem of unnecessary triggering, can be overcome without the considerable additional complexity, cost, and speed penalty of having nodes which must extract the alarm, modify it and send it on.

Protection switching trigger generation

A loopback mechanism uses frame relay OAM loopback frames which eliminate the need for location identifiers and reduces overhead and complexity. The frames replace source and destination loopback location identifiers by a loopback indicator field, a send node count field and a return node count field. The originating node of the loopback procedure sets the number of intermediate frame relay nodes to be traversed. The intermediate frame relay nodes simply increment or decrement the node count, depending on the direction of the loopback frame.

Growing community of inventors

Nepean, Canada

Khalid Ahmad