A Comparative Performance Evaluation of DCCP

Interest continues to grow in alternative transport protocols to the Transmission Control Protocol (TCP). These alternatives include protocols designed to give greater efficiency in high-speed, high-delay environments (so-called high-speed TCP variants), and protocols that provide congestion control without reliability. For the former category, along with the deployed base of 'vanilla' TCP - TCP NewReno - the TCP variants BIC and Cubic are widely used within Linux: for the latter category, the Datagram Congestion Control Protocol (DCCP) is currently on the IETF Standards Track. It is clear that future traffic patterns will consist of a mix of flows from these protocols (and others). So, It is important for users and network operators to be aware of the impact that these protocols may have on users. We assess the performance of DCCP CCID2 relative to TCP NewReno, and variants BIC and CUBIC, all in "out-of-the box" configurations. We use a testbed and end-to-end measurements to assess overall throughput, and also to assess fairness - how well these protocols might respond to each other when operating over the same end-to-end network path. We find that DCCP CCID2 shows good fairness with NewReno under our test conditions, while BIC and CUBIC show unfairness above round-trip times of 25ms.