AFEC: an adaptive forward error correction protocol for end-to-end transport of real-time traffic

This paper presents an adaptive protocol for packet-level forward error correction in dynamic networks. The objective is to facilitate end-to-end transport of real-time traffic whose timing constraints rule out the use of retransmission-based congestion control and quality of service (QoS) provision schemes. The degree of redundancy injected into the network is adjusted as a function of the network state, decreasing when the network is well-behaved and increasing when it is not. The control problem is nontrivial due to the fact that increased redundancy, beyond a certain point, can backfire resulting in self-induced congestion which impedes the timely recovery of information at the receiver. First, we give a comprehensive analysis of the control problem associated with adaptive forward error correction, concentrating on the dynamics of a particular protocol called adaptive forward error correction (AFEC). We show that instabilities can arise from two distinct sources-the desired operating point and network delay-and we give solutions to handle them. The first factor is determined by the stringency of the application´s QoS requirements, making its achievement potentially perilous. Second, we present simulation results showing the dynamics of AFEC and comparing its performance against static FEC. We study the efficacy of AFEC under structural perturbations and bursty traffic conditions, and we quantitatively estimate the redundancy recovery rate function which relates redundancy to the QoS rendered at the receiver. We show that the curve is unimodal, its curvature being determined by whether a connection is packet loss or delay dominated