Tradeoffs between retransmission and forward error correction in the RTP stack

Abstract: Video conferencing applications has reached worldwide usage in recent years by the help of the improvements in network infrastructures for public services. Media data covers a significant ratio of data traffic over IP networks. However, it is challenging to ensure a decent quality of service (QoS) on public networks in terms of video and audio quality. The main factor that may cause degradation in media playback quality is packet losses. There are various techniques available to conceal packet losses in lossy channels. According to the application needs and channel characteristics such as loss patterns and round trip times, retransmission or forward error correction techniques may be applied at application level. These two techniques have different challenges which lead to tradeoffs between them, thus one might be chosen over the others. In this thesis work, retransmission’s worst case performances under considered packet loss patterns and various round trip times are compared to performances of forward error correction schemes. In addition, implementation details with respect to the relevant RFCs are provided as an example to give a better judgement on the obtained results. Results obtained under the packet loss patterns that are generated with a simple Gilbert-Elliot 2-state model shows that forward error correction techniques are a reasonable choice of error concealing in the real-time transport protocol (RTP) stack where round trip time in the channel is greater than 200 ms. In addition, bandwidth overhead revealed by forward error correction stays higher than retransmission’s bandwidth overhead in all sample runs. In cases where round trip times are high, then the choice of forward error correction scheme is bound to the packet loss pattern. In the results section, it is obtained that ReedSolomon performs well in terms of residual packet losses, which are the packets not being recovered, and bandwidth overhead when losses occur in long bursts.