Importance

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Abstract

In the event of a failure on a transmission line, a sender, or a terminal node of the failed line, broadcasts CONTROL packets to each of all adjacent tandem nodes, containing a hop count and node trace data. In response to a CONTROL packet, each tandem node increments the hop count of the packet, updates its node trace data, makes a record of all arriving CONTROL packets, and broadcasts copies of each arriving CONTROL packet to adjacent nodes if the hop count is smaller than a prescribed value. A chooser, which is the other terminal node of the failed line, responds to CONTROL packets from a given node for sending back to the given node as many RETURN packets as there are failed channels. Each tandem node makes a record of all arriving RETURN packets, checks the node trace data of each RETURN packet against that of the CONTROL packets in the record to detect if there is a spare channel to an adjacent node on a route to the sender with a least hop count, transmits each RETURN packet to it if a spare channel is detected, or causes retransmission of a RETURN packet from the chooser to another tandem node if no spare channel is detected. The sender responds to each RETURN packet by switching a link from a failed channel to a spare channel indicated by the packet. An END packet is sent back from the sender to each tandem node along which the RETURN packet travelled between the chooser to the sender. On reaching the chooser, the END packet is used to switch a link from a failed channel to a spare channel indicated by the received END packet.

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First Claim