TCP Aware Multi-user Scheduling: Avoid Spurious TCP Timeout due to Delay Spikes

TCP Aware Multi-user Scheduling

Avoid Spurious TCP Timeout due to Delay Spikes

While other studies on TCP over wireless discuss the impact of channel instability in terms of packet losses, rate and delay variation, we performed a systematic study of interaction between scheduling algorithm and TCP performance. Conventional MAC scheduling is done by observing channel throughput at MAC layer without any consideration of the related impact on TCP performance. As users could experience potential long scheduling intervals and thus large variability in packet roundtrip time due to channel variations, TCP may interpret variability as packet losses or congestion. But packets are merely held up in MAC buffer. Hence, careless scheduling algorithm can lead to spurious TCP timeouts. While new approaches that make TCP more robust to timeouts by changing TCP procedures face the challenge of interoperating with diverse wireless characteristics, TCP-aware scheduling provides simple solutions to shield TCP from large channel variations. We modify existing scheduling algorithms to reflect system performance that TCP observes. In particular, while proportional fair scheduler is to achieve fairness at MAC layer, TCP aware proportional fair scheduler achieves proportional fairness in terms of TCP throughput. The design focus is at MAC layer who only needs information on the type of the traffic (TCP or UDP), and no alternation is done at TCP layer.

Enhanced Scheduling Algorithms for Improved TCP Performance in Wireless IP Networks
Thierry Klein, Kin Leung, Haitao Zheng
IEEE Globecom, Dallas, TX, Nov. 2004
[Abstract, PDF]
A journal version is under review.
Slides: coming soon!
Haitao Zheng, April 16, 2005