Nortel Networks Corporation

Northern Telecom Limited

Mark Bentall

Brian Charles Hargrave Turton

Brian Charles Turton

Philip Charlesworth

Christopher William Lewis Hobbs

In a cell-based transmission protocol such as ATM, a Cyclic Redundancy Check code is used for error detection at a frame level, and a Hamming code is used for error correction at the cell level, to improve error protection, and reduce the need for retransmission. The method can be used as a modification to ATM Adaption Layers.

Cell based data transmission method

Data packets are transmitted over a communications link in an interleaved manner. The link comprises a series of time-division multiplexed (TDM) frames, each frame comprising a plurality of time slots, a time slot being shorter than a data packet. Data packets are transmitted over a series of the TDM frames, one time slot in each of the series of frames being used to transmit a portion of that data packet. Different ones of the data packets begin in different TDM frames. Received data packets are allocated a modified header for use over the communications link. The modified header has a shorter address than the address in the received packet header and the modified header can be split into a plurality of parts which are distributed across the length of the transmitted packet. Error protection for the modified header can also be distributed across the length of the transmitted packet and is preferably spaced, within the transmitted packet, from the other parts of the modified header by payload parts of the packet.

Data interleaving method

Following failure of part of the network, a restoration process is carried out. A restoration route around the failed part is selected, and at least a portion of the capacity of links along the restoration route is allocated. The restoration route may be completed without delay. If it can be optimised subsequently, it will be changed, to eliminate any loops, or to use routes further away from the failed part, to avoid congestion close to the failed part.

Network restoration routing optimization

For restoration of a network a plurality of possible alternative routes are determined. Messages are passed between nodes along the alternative routes to determine a spare capacity of each link in the alternative routes. An alternative route is selected from the possible alternative routes on the basis of a database of the determined link spare capacities for each of the possible alternative routes, built up at a chooser node at one side of the failed part of the network.

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Gwent, United Kingdom

Mark Bentall