Layered Error - Control Coding for Ip Multicast


single retransmitted packet). For instance, a receiver subscribes to the lowest redundancy layer out of two layers. Thus, it has the protection of a pure (3, 2) parity code. If packets 1 and 2 of one block are lost, then it could request 1 or 2; alternatively it could request parity packets for packet 0 and 1, or for packets 2 and 3. The peer handling the request may have further requests from other receivers and should try to meet them with as few packets as possible. If the repeat request states explicitly which packet it should send, then it has little flexibility to coordinate responses (if packet 1 is requested by one and packet 2 by all others, it would have to send both even if packet 2 would have been equally acceptable by the receiver considered in the example). To allow a peer most flexibility in issuing repair packets, we let the repeat request contain the indices of the incorrigible columns of the decoding structure it uses (states the number of layers it receives). Thus, the peer can decide on the best response whether it is retransmission of data packets or additional redundancy packets. All repeat requests as well as the responses are issued at the data layer. A remaining issue to determine is the duration to keep a packet at a receiver in order to answer all repeat request it may get. We can consider two cases: first, a receiver which never received and answered repeat requests is not known by any other receiver and does not need to keep past packets. If it receives a request, it will therefore not be able to handle it and the receiver issuing the request will continue to increase the scope until it gets an answer. If the receiver which did not answer should answer future requests then it can determine the length of needed history, as in the following case, and start accumulating it. Second, a receiver which occasionally answers requests will need to keep past packets in anticipation of further requests. Since an incorrigible loss leads instantaneously to a repeat request, the peer can determine the length of the needed history that it should keep by comparing the requested packet number with the current packet number. Note that repeat requests and their responses are not counted in the total session rate; it is only enforced by the transmitter …

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Cite this paper

@inproceedings{Bolot1997LayeredE, title={Layered Error - Control Coding for Ip Multicast}, author={J F Bolot and Andr{\'e}s Vega-Garc{\'i}a}, year={1997} }