I. Introduction
Layered coding (LC) and multiple description coding (MDC) have been proposed as source coding schemes that can offer robust communication over packet loss channels. In contrast to traditional coding schemes that generate a single bitstream, LC and MDC generate two or more bitstreams. In LC, one bitstream is sent as a base layer and the other bitstreams are successive enhancement layers. The base layer has higher priority than the enhancement layers as the loss of the base layer makes the information received from the enhancement layers useless. An enhancement layer can be decoded only if the base layer and all previous enhancement layers have been correctly received. Automatic repeat request (ARQ) or forward error correction (FEC) is generally employed for error control in the base layer. In the rest of this paper, unless otherwise noted, the base layer of LC is transmitted using ARQ (and requisite error detection coding). The multiple bitstreams (descriptions) of MDC, however, are equally important. Any subset of the bitstreams is decodable, and reconstruction quality improves with the size of the subset. One means of realizing MDC is using FEC codes [1].