High errors and high delays create well-known problems with TCP. One established approach to solve this problem involves dividing TCP connections into segments, or splitting the connection. This paper takes this approach one step further by exploring the use of a TCP proxy on board a satellite for the purpose of enhancing end-to-end TCP performance. We show that this approach yields a number of important advantages, especially for small, mobile terminals, multi-segment systems, and multicast applications. As part of this architecture, we introduce a method of TCP backpressure using the advertised window, which optimizes memory usage on the satellite. Using simulation, we demonstrate that performance may improve by as much as three-fold.

TCP performance can be significantly affected when the buffer capacity at routers is small. This is possible when either many flows share the network or the bandwidth-delay product is large (e.g. satellite links). The behavior of various versions of TCP with respect to buffer capacity issues has not been studied in much detail. We investigate the behavior and performance of different TCP variants under small buffer capacity conditions. We recognize TCP pacing as a potential solution. However, instead of using TCP's sending rate as the dictating metric, we make use of the bandwidth-share estimate (BSE), maintained by TCP Westwood, to set the pacing interval. We call this newly proposed protocol paced-Westwood. We also show the need to scale BSE further to mitigate the effects of positive feedback in BSE. For this, we propose a further enhancement that we call /spl alpha/-paced Westwood that uses a scaling parameter /spl alpha/ to enforce convergence of BSE and the pacing interval. The proposed /spl alpha/-paced Westwood uses its BSE to space the packet bursts during the slow-start phase, resulting in a superior throughput in the troublesome low buffer capacity cases. With the help of simulations, we show that our enhanced TCP Westwood outperforms both unpaced as well as paced TCP NewReno under low buffer capacity networks.

We study the performance metrics associated with TCP-regulated traffic in multi-hop wireless networks that use a common physical channel (e.g., IEEE 802.11). In contrast to earlier analyses, we focus simultaneously on two key operating metrics - the energy efficiency and the session throughput. Using analysis and simulations, we show how these metrics are strongly influenced by the radio transmission range of individual nodes. Due to tradeoffs between the individual packet transmission energy and the likelihood of retransmissions, the total energy consumption is a convex function of the number of hops (and hence, of the transmission range). On the other hand, the TCP session throughput decreases supra-linearly with a decrease in the transmission range. In certain scenarios, the overall network capacity can then be a concave function of the transmission range. Based on our analysis of the performance of an individual TCP session, we finally study how parameters such as the node density and the radio transmission range affect the overall network capacity under different operating conditions. Our analysis shows that capacity metrics at the TCP layer behave quite differently than corresponding idealized link-layer metrics.

Emerging technologies such as Bluetooth are expected to become a ubiquitous solution for providing short range, low power, low cost, pico-cellular wireless connectivity. Bluetooth is a master driven time division duplex (TDD) system that supports an asynchronous channel for data traffic as well as synchronous channels for voice traffic. Data applications running over Bluetooth such as http, ftp and real audio will need transport layer protocols such as TCP and UDP to send packets over the wireless links. In this paper we study several schemes designed to improve the performance of asynchronous data traffic over a Bluetooth piconet that supports multiple active slaves. We propose and compare a number of segmentation and reassembly policies and MAC scheduling algorithms with a view towards enhancing the performance of transport layer sessions. We investigate the effect of different FEC and ARQ schemes at the baseband level, using a two-state Markov channel model for the Bluetooth RF link. We also study how the presence of circuit-switched voice impacts the performance of data traffic.