Experimental performance of DCCP over live satellite and long range wireless links

We present experimental results for the performance over satellite and long range wireless (WiMax) links of the new TCP-Friendly Rate Control (TFRC) congestion control mechanism from the Datagram Congestion Control Protocol (DCCP) proposed for use with real-time traffic. We evaluate the performance of the standard DCCP/CCID3 algorithm and identify two problem areas: the measured DCCP/CCID3 rate is inferior to the rate achievable with standard TCP and a significant rate oscillation continuously occurs making the resulting rate variable even in the short term. We analyse the links and identify the potential causes, i.e. long and variable delay and link errors. As a second contribution, we propose a change in the DCCP/CCID3 algorithm in which the number of feedback messages is increased from the currently standard of at least one per return trip time. Although it is recognised that the increase in control traffic may decrease the overall efficiency, we demonstrate that the change results in higher data rates which are closer to what is achievable with TCP on those networks and that the overhead introduced remains acceptable.