Avoiding spurious TCP timeouts in wireless networks by delay injection

Abstract

-The transmission control protocol (TCP) has been designed to provide reliable transport of packets by adjusting the transmission rate to the network congestion level. While TCP can adapt to small fluctuations in the delay between the sender and the receiver, adverse affects (most importantly spurious timeouts) have been observed under large delay variability. In this paper, we exhibit the presence of such delay spikes in wireless networks and discuss their possible origins. We then investigate a new methodology for avoiding spurious TCP timeouts by appropriately injecting additional random delay along the communication path. Different algorithms for the delay injection are presented and we assess their relative performances and merits through simulations. In particular we show by numerical examples that the delay injection methodology can significantly decrease the number of timeouts and increase the achieved TCP throughput by about 8% in the network scenario considered in this paper. One of the attractive features of the new methodology is that it does not require any changes to the TCP protocol and can be applied independently of the TCP version used.

Spurious TCP Timeouts in 802.11 Networks

“…Both actually identify a low rate of spurious timeouts in live networks. Techniques have been proposed to reduce spurious timeouts, such as [6] where random delay was artificially added by the network to the RTT was explored as a way to increase the timeout. In [7] this technique was explored in the context of 802.11 networks with bursty outages simulated by dropping n consecutive packets out of every 100, and found to be sometimes beneficial.…”

PAQ: A Starvation-Resistant Alternative to Proportional Fair

“…2) Natural Channel Variations: The second scenario in which PF can induce starvation occurs due to natural variations in the achievable rate (also, see [9]). For instance, consider a system with 2 ATs -AT1 and AT2.…”

“…We start by using prior work [2], [9] and simulations to show that PF-induced starvation is due to one of two reasons -"on-off" traffic patterns and certain types of natural channel variations. For each of these, we identify the reason why PF can induce starvation and propose mechanisms to prevent it.…”

Techniques for Throughput Enhancement in Wireless Networks

“…For further enhancement, delay-jitter algorithm has been proposed and studied in [9] and [10]. With clear knowledge that delay causes spurious timeouts, one way of maintaining throughput performance is to absorb the delay variability by a large timeout value.…”

“…Furthermore, the TCP sender at the proxy server can be modified once the need arises for split-TCP solution in a network by increasing the m value. More so the objective of both methods is to avoid spurious timeouts as a solution to sustaining throughput performance, the jitter-algorithm [9,10] achieves an increased RTO value through injection of extra delay to RTTs as a way of increasing the mean deviation (Equation 3), while the increase of smoothed average RTT is kept minimal. Although the proposed method in this paper is to increase the m value in equation 3 and thereby achieve the increase in RTO.…”