TCP Prairie: a sender-only TCP modification based on adaptive bandwidth estimation in wired-wireless networks

Abstract

This paper presents a new TCP (Transmission Control Protocol) variant called TCP Prairie which is a sender-only TCP modification based on dynamic bandwidth estimation in wired-cum-wireless networks. The key idea here is to continuously measure the bandwidth used by a TCP flow via monitoring the rate of returning acknowledgements (ACKs) and the round-trip time (RTT) values. The estimated bandwidth is then used to set the congestion window ( cwnd) and the slow-start threshold ( ssthresh) after a slowdown event (i.e. after three duplicate ACKs or after a timeout). The distinguishing feature of TCP Prairie (compared to other TCP variants such as TCP Westwood which also uses bandwidth estimation-based congestion control) is that it exploits the burstiness pattern of ACK arrivals and estimates the available bandwidth more accurately. For the proposed bandwidth estimation mechanism, the bandwidth sample is calculated by distributing a burst of ACKs over an off period based on degree of congestion and burstiness in the network. The estimation technique is robust against burstiness of ACK arrival and type of loss (e.g. wireless loss, congestion loss). Due to a more accurate bandwidth estimation, during congestion control the TCP Prairie sender sets the slow-start threshold to a value which is consistent with the available bandwidth for the corresponding TCP flow. Simulation results obtained using ns-2 reveal that TCP Prairie provides significant throughput performance improvement over TCP New-Reno and TCP Westwood under congestion and/or wireless loss scenarios. Also, compared to TCP Westwood, TCP Prairie is observed to be more friendly towards TCP New-Reno.