Recovery of small bursts of voice packets using RS erasure code with low decoding delay

Abstract

It is well known that packet losses in the networks are mainly due to congestion because of the finite buffer capacity of queues in routers. Forward error correction (FEC) can recover from losses without retransmissions of lost packets. However, FEC faces with two main drawbacks: firstly, the redundancy generated by the sender increases the overall load of the network resulting in an increase of loss rate and secondly, waiting for redundant information to be able to recover lost packets results in additional delay. In this paper we employ the Reed Solomon erasure (RSE (7, 4)) code to recover lost packets. We apply the adaptive differential pulse code modulation (ADPCM) compression technique to make room for the redundant packets and thus reduce the additional load due to redundancy. We further modify the recovery scheme to bring down the decoding delay from a maximum of 6 packets to a maximum of 3 packets. Results of informal mean opinion score (MOS) listening test show that the modified RSE code is capable of correcting any burst of two packets and provides a tradeoff between quality, network load and decoding delay.