This document is a survey of Performance Enhancing Proxies (PEPs) often employed to improve degraded TCP performance caused by characteristics of specific link environments, for example, in satellite, wireless WAN, and wireless LAN environments. Different types of Performance Enhancing Proxies are described as well as the mechanisms used to improve performance. Emphasis is put on proxies operating with TCP. In addition, motivations for their development and use are described along with some of the consequences of using them, especially in the context of the Internet.

/pdf/performance-enhancing-proxies-intended-to-mitigate-link-114ytqw0rj.pdf

Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations

Wireless access networks in the form of wireless local area networks, home networks, and cellular networks are becoming an integral part of the Internet. Unlike wired networks, random packet loss due to bit errors is not negligible in wireless networks, and this causes significant performance degradation of transmission control protocol (TCP). We propose and study a novel end-to-end congestion control mechanism called TCP Veno that is simple and effective for dealing with random packet loss. A key ingredient of Veno is that it monitors the network congestion level and uses that information to decide whether packet losses are likely to be due to congestion or random bit errors. Specifically: (1) it refines the multiplicative decrease algorithm of TCP Reno-the most widely deployed TCP version in practice-by adjusting the slow-start threshold according to the perceived network congestion level rather than a fixed drop factor and (2) it refines the linear increase algorithm so that the connection can stay longer in an operating region in which the network bandwidth is fully utilized. Based on extensive network testbed experiments and live Internet measurements, we show that Veno can achieve significant throughput improvements without adversely affecting other concurrent TCP connections, including other concurrent Reno connections. In typical wireless access networks with 1% random packet loss rate, throughput improvement of up to 80% can be demonstrated. A salient feature of Veno is that it modifies only the sender-side protocol of Reno without changing the receiver-side protocol stack.

/pdf/tcp-veno-tcp-enhancement-for-transmission-over-wireless-4v3ws0osle.pdf

TCP Veno: TCP enhancement for transmission over wireless access networks

Current TCP protocols have lower throughput performance in satellite networks mainly due to the effects of long propagation delays and high link error rates. In this paper, a new congestion control scheme called TCP-Peach is introduced for satellite networks. TCP-Peach is composed of two new algorithms, namely Sudden Start and Rapid Recovery, as well as the two traditional TCP algorithms, Congestion Avoidance and Fast Retransmit. The new algorithms are based on the novel concept of using dummy segments to probe the availability of network resources without carrying any new information to the sender. Dummy segments are treated as low-priority segments and accordingly they do not effect the delivery of actual data traffic. Simulation experiments show that TCP-Peach outperforms other TCP schemes for satellite networks in terms of goodput. It also provides a fair share of network resources.

/pdf/tcp-peach-a-new-congestion-control-scheme-for-satellite-ip-ctdf5e1ckc.pdf

TCP-Peach: a new congestion control scheme for satellite IP networks

TCP-Peach: A New Congestion Control Scheme for

We present a simple scheme which enables a TCP receiver to distinguish congestion losses from corruption losses. The scheme works in the case where the last hop to the receiver is a wireless link and has the smallest bandwidth among all links on the connection path. We added our mechanism to TCP-Reno to evaluate the performance improvement. We compared our scheme against Ideal TCP-Reno which is TCP-Reno that can perfectly (but artificially) distinguish between congestion losses and wireless transmission losses. Under favourable conditions, our scheme performs similar to Ideal TCP-Reno and can lead to significant throughput improvement.

/pdf/discriminating-congestion-losses-from-wireless-losses-using-3oqlfzjhhb.pdf

Discriminating congestion losses from wireless losses using inter-arrival times at the receiver

This document outlines possible TCP enhancements that may allow TCP to better utilize the available bandwidth provided by networks containing satellite links. The algorithms and mechanisms outlined have not been judged to be mature enough to be recommended by the IETF. The goal of this document is to educate researchers as to the current work and progress being done in TCP research related to satellite networks.

T. Henderson

Papers

Ongoing TCP Research Related to Satellites