Light-weight congestion control for the DCCP: Implementation in the linux kernel

Abstract

The DCCP complements the UDP with three TCP-friendly congestion control modes. The most important are the CCID 2 mode, which uses the TCP’s congestion control mechanism, and the CCID 3 mode, which implements the TFRC congestion control. The CCID 3 is intended for general multimedia transmission, although the authors of the DCCP specification notes that it may caused problems in the case of high-bandwidth video transmissions. This paper presents a prototype implementation of the modified TFRC congestion control, designed for multimedia transmission, that uses the RTP linear throughput equation (instead of the TCP one, originally used by the TFRC). This solution was introduced by the Authors in their previous work. The prototype implementation in the Linux kernel includes both a new congestion control module and updates to the DCCP kernel API. The proposed solution causes the DCCP to be not fully TCP-friendly, but still remains TCP-tolerant and does not cause unnecessary degradation of competing TCP flows. As a result, this method of congestion control can be used wherever it is necessity to use a TCP-tolerant protocol and when the rate of the media stream cannot be limited in a way typical for the TCP.