Abstract

This paper presents an early experience with a CDMA 2.5G wireless network commercially deployed in South Korea. It finds that there are high signal losses and latency commonly present in packet delivery causing TCP to under-utilize the available network bandwidth significantly. In this environment, there is inherent limitation in using packet losses as congestion indicators because of lack of correlation between congestion and packet losses. To remedy this problem, a new flow control protocol that uses delay hysteresis as a congestion indicator is presented. The protocol actively manages delays to keep them within a certain bound by throttling its transmission rate when network delays tend to increase and also probing for more bandwidth when network delays tend to decrease. A variant of the protocol is currently incorporated in a cellular-phone based video-ondemand system as the main transport protocol for video file download and also for streaming. Our experiment results suggest that the protocol achieves higher and more consistent throughput than TCP, and exhibits some degree of fairness to its own flows and TCP.

Citations