An evaluation of RTP circuit breaker performance on LTE networks

Real-time multimedia comprises a large, and growing, fraction of mobile data traffic. An important subset of such flows are from interactive conferencing applications using RTP on UDP/IP to reduce latency. UDP has no congestion control, and while the IETF is developing RTP-level congestion control algorithms as part of the WebRTC standards, these will take time to finalise and deploy. In the interim, we proposed an RTP circuit breaker to the IETF. This can detect and stop RTP flows that cause excessive network congestion, acting as an envelope within which a congestion control algorithm can operate. We briefly review the design of the RTP circuit breaker, then present an initial evaluation of its performance on LTE networks. Our results show that the algorithm is conservative in overload situations with low delay and high loss. Such situations can occur due to active queue management in LTE networks. We propose changes to the RTP circuit breaker to better suit such networks, by using a different TCP throughput model that is more sensitive to the observed packet loss patterns.