TCP has been designed and tuned to perform well under the assumption that all losses are an indication of congestion. When a TCP connection traverses a wireless link, packets may be lost due to wireless transmission errors, in addition to congestion losses. TCP implicitly assumes that all packet losses are due to congestion, and triggers congestion control mechanism when a packet loss is detected. It has been previously demonstrated that this feature of TCP affects performance adversely when packets are lost due to transmission errors. To avoid the performance degradation, techniques to distinguish between corruption and congestion losses without any explicit information from the network (routers or switches) are of interest.

TCP is a popular transport protocol used in present-day internet. When packet losses occur, TCP assumes that the packet losses are due to congestion, and responds by reducing its congestion window. When a TCP connection traverses a wireless link, a significant fraction of packet losses may occur due to transmission errors. TCP responds to such losses also by reducing congestion window. This results in unnecessary degradation in TCP performance. We define a class of functions named loss predictors which may be used by a TCP sender to guess the actual cause of a packet loss (congestion or transmission error) and take appropriate actions. These loss predictors use simple statistics on round-trip times and/or throughput, to determine the cause of a packet loss. We investigate their ability to determine the cause of a packet loss. Unfortunately, our simulation measurements suggest that the three loss predictors do not perform too well. 1. Introduction TCP is a popular protocol for reliabl...

this paper will touch on current topics in many areas of networking. From cryptography to routing, from billing to expanded techniques for automatic configuration, mobility changes the way we think about computing, and invalidates some of the design assumptions upon which current network protocols and products have been built

The explosion of the e-community has spurred the need for a more global communication paradigm. Today, more people than ever are using mobile ad hoc networks to fulfill their communication needs. In particular, LEO satellite access networks are gaining popularity as an alternative or a complimentary way to get connected. Being both wireless and mobile, these networks have a unique set of link errors including bit corruption, handoff and limited connectivity. Unfortunately, most transport protocols, like the standard TCP, are only designed to handle congestion-related errors common in wired networks. This inability to handle multiple kinds of errors results in severe degradation in effective throughput and energy saving, which are relevant metrics for a mobile ad hoc environment. A recent study proposed a new transport protocol for satellites called STP that addressed many of the unique problems of satellite networks. However, there was no explicit attempt to implement a differentiating error control strategy in that protocol. This thesis proposes grafting a new probing mechanism in STP to make it more responsive to the prevailing error conditions in the network. The mechanism works by investing some time and transmission effort to deduce the cause of error. However, this overhead is recouped by handsome gains in both the connection's effective throughput and its energy efficiency. This sender-only mechanism leverages many unique features of STP, making it simple, scalable and easy to deploy. The mechanism's unique semantics make it quick to start and finish, yet efficient by its ability to self-terminate if it has prematurely started. Most importantly, the mechanism also preserves the end-to-end semantics of STP. The simulation compares the STP protocol both with and witho...

The success of the Internet can be attributed directly to the large number of useful applications running on it. TCP/IP has been the underlying communication protocols enabling these applications. Despite the widespread deployment of the protocols, TCP/IP continues to be a hot research topic among R&D teams in the academia as well as the industry. Much of the recent work has been centered on adapting the protocols for use in wireless environments because of its ease of deployment, convenience to users, and high bandwidth brought about by maturing of advanced technologies (e.g., 3G and IEEE802.11 LAN). The next big wave -- mobile Internet, in which wireless will play a necessary part of the Internet infrastructure -- is around the corner. The original TCP design assumes packet loss is always induced by congestion. This assumption can lead to significant performance degradation in wireless networks where random loss due to environmental noise is rampant. The detrimental effect of random loss on TCP performance is a well-known outstanding problem that remains to be unsolved. This dissertation proposes and studies a novel end-to-end congestion control mechanism called TCP Veno that is able to deal with random loss effectively. Veno differs from the conventional TCP in a major way: it monitors the congestion level using an end-to-end estimation algorithm and uses that knowledge to refine the congestion control algorithm of TCP. Specifically, 1) it refines the multiplicative decrease algorithm of Reno by setting the congestion threshold -- a key control parameter in TCP - according to the perceived congestion level of the network instead of a fixed drop factor when packet loss is detected; 2) it vi refines the linear increase algorithm by attempting to stay longer in an op...

A number of designs have been proposed for complementing TCP’s treatment of packet loss as an implicit signal of congestion, with a signal derived from measurements of round-trip times (RTT). The premise of such delay-based congestion estimators (DBCEs) is that congestion is reflected in queueing delays that can be detected by measuring changes in RTT. We conduct a large-scale empirical analysis of real-world TCP connections to evaluate the effectiveness and limitations of five prominent DBCEs. Our findings are that none of the five perform well (correctly indicate congestion before a loss is experienced) for a large percentage of real-world TCP connections. They also often perform poorly by having high rates of false-positive and false-negative estimates of congestion. Further, we find that the connection characteristics that most influence the performance of these DBCEs are so diverse that designing an effective DBCE for all types of connections is still an open research problem. 1 1

Keywords: Wireless network, explicit congestion notification, TCP/IP, congestion control Abstract: TCP was designed for wireline networks, where loss events are mostly caused by network congestion. The congestion control mechanism of current TCP uses loss events as the indicator of congestion, and reduces its congestion window size. However, when a lossy link is involved in a TCP connection, non-congestion random losses should also be considered. The congestion window size should not be decreased if a loss event is caused by link corruptions. To improve TCP performance over lossy links, in this paper, we first present that zero congestion loss could be achieved by appropriately setting the ECN marking threshold in the RED buffer. Secondly, we propose a new TCP algorithm, called Differentiation Capable TCP (Diff-C-TCP). Diff-C-TCP makes an assumption that packet losses are caused by link corruptions, and uses ECN (Explicit Congestion Notification) to determine any loss that may occasionally happen due to network congestion. We have shown that Diff-C-TCP performs very well in the presence of a lossy link. 1

Being both wireless and mobile, low Earth obiting (LEO) satellite access networks have a unique set of link errors including bit corruption, handoff, and limited connectivity. Unfortunately, most transport protocols are only designed to handle congestion-related errors common in wired networks. This inability to handle multiple kinds of errors results in severe degradation in effective throughput and energy saving, which are relevant metrics for a wireless and mobile environment. A recent study proposed a new transport protocol for satellites called STP that addresses many of the unique problems of satellite networks. There was, however, no explicit attempt to implement a differentiating error control strategy in that protocol. This paper proposes grafting a new probing mechanism in STP to make it more responsive to the prevailing error conditions in the network. The mechanism works by investing some time and transmission effort to determine the cause of error. This overhead is, however, recouped by handsome gains in both the connection’s effective throughput and its energy efficiency. Manuscript received January 16, 2004; revised September 27, 2004; released for publication November 18, 2004.

draft-ietf-pilc-error-00.txt This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Comments should be submitted to the PILC mailing list at

this document, we survey the different solutions available or under investigation, and issue the corresponding recommendations. The subsequent sections include solutions: unrelated to IP built on top of IP built on top of UDP built on top of TCP (modifying TCP) The latter solutions constitute the most numerous group, as it is very desirable to make TCP, the most widely used protocol in the internet, perform well over wireless networks. There is a large body of work on the subject of improving TCP performance over satellite links. The documents that the tcpsat working group of the IETF is working on [AG98, AGGHSSTT98] are very relevant. In both cases, it is essential to start by improving the characteristics of the medium by using forward error correction (FEC) at the link layer to reduce the BER (bit error rate) from values as high as 10