Sequential Use of Block Codes and Convolutional Codes in a Real-Time Multi-Hop Network

Real-time streaming of audio and video have tight constraints on the delay allowed at each step in the distribution chain. In this paper, we focus on the transport layer. That is, we investigate the effect of imposing a maximum allowable delay on the symbol loss probability for a set of rate 1/2 erasure correcting codes. We define the effective symbol loss probability to be the probability that a symbol is received too late or not at all, given some maximum allowable delay. We consider networks where the source and sink communicate via a relaying node, and that this intermediate node performs recoding. The erasure correcting code used between the source and relay need not be the same as the erasure correcting code used between the relay and sink. Moreover, on the first link, we use both a block code and on the second link we use a convolutional code. In order to do a fair comparison, we also include the case where both links use the same code type. Our results show that in order to minimize the effective symbol loss, the first link should use a triangular block code. Whereas, the second link should use a convolutional or triangular code, with little to no gain of using the former over the latter.