Performance Evaluation of CoDel Queue Mechanism and TFRC Transport Protocol when Using VoIP Flows

There is an increasing demand for delivering real-time interactive voice traffic with Quality of Experience (QoE) requirements over a best-effort IP network. Therefore, the use of either TCP or UDP has become problematic since TCP is not well suited for interactive traffic and UDP is unresponsive to congestion. As a result a number of Congestion Control Mechanism (CCM) have been proposed with emphasis on achieving fair share of network resources among competing flows, but little attention has been paid to the QoE requirements of interactive applications. Furthermore, such traffic is affected by the bufferbloat phenomenon, which causes high latency and jitter. Therefore, intelligent queue management techniques need to be explored for this problem. This paper experimentally evaluates and analyses the performance benefits for VoIP using a Congestion Framework, which includes: (a) the congestion responsive transport protocol TFRC and (b) Active Queue Management (AQM) variant, called Controlled Delay (CoDel) at the network layer. The simulations were carried in network simulator, ns2, to evaluate how CoDel maintains QoE if round trip time (RTT) between source and destination is increased. The findings show that CoDel can maintain QoE for the VoIP flows under RTTs of 160 ms, however over longer RTTs the network queue size is larger compared to RED the delay experienced is greater, which impacts the overall end-to-end delay, hence loss of QoE.