Reliable transport protocols such as TCP are tuned to perform well in traditional networks where packet losses occur mostly because of congestion. However, networks with wireless and other lossy links also suffer from significant losses due to bit errors and handoffs. TCP responds to all losses by invoking congestion control and avoidance algorithms, resulting in degraded end-to-end performance in wireless and lossy systems. In this paper, we compare several schemes designed to improve the performance of TCP in such networks. We classify these schemes into three broad categories: end-to-end protocols, where loss recovery is performed by the sender; link-layer protocols, that provide local reliability; and split-connection protocols, that break the end-to-end connection into two parts at the base station. We present the results of several experiments performed in both LAN and WAN environments, using throughput and goodput as the metrics for comparison. Our results show that a reliable link-layer protocol that is TCP-aware provides very good performance. Furthermore, it is possible to achieve good performance without splitting the end-to-end connection at the base station. We also demonstrate that selective acknowledgments and explicit loss notifications result in significant performance improvements.

We present the design and implementation of an end-to-end architecture for Internet host mobility using dynamic updates to the Domain Name System (DNS) to track host location. Existing TCP connections are retained using secure and efficient connection migration, enabling established connections to seamlessly negotiate a change in endpoint IP addresses without the need for a third party. Our architecture is secure---name updates are effected via the secure DNS update protocol, while TCP connection migration uses a novel set of Migrate options---and provides a pure end-system alternative to routing-based approaches such as Mobile IP. Mobile IP was

We present extensions to a traditional cellular [Ses95] handoff system to handle the simultaneous operation of multiple wireless network interfaces. This new system allows mobile users to roam in a "Wireless Overlay Network" structure consisting of room-size, building-size, and wide-area data networks. In this structure, the user can connect to the wired network through multiple wireless subnets, and offers the best possible connectivity given the user's geographic location and local wireless connectivity. We present the basic handoff system and show that the handoff latency is bounded by the amount of time that the mobile host takes to discover that it has moved in or out of a new wireless overlay. To efficiently support applications that can not tolerate these disruptions, we present optimizations to this basic scheme that assume no knowledge about specific channel characteristics. For handoffs between room-size and building-size overlays, these optimizations lead to a handoff latenc...

Abstract. Wireless networking has witnessed an explosion of interest from consumers in recent years for its applications in mobile and personal communications. As wireless networks become an integral component of the modern communication infrastructure, energy efficiency will be an important design consideration due to the limited battery life of mobile terminals. Power conservation techniques are commonly used in the hardware design of such systems. Since the network interface is a significant consumer of power, considerable research has been devoted to low-power design of the entire network protocol stack of wireless networks in an effort to enhance energy efficiency. This paper presents a comprehensive summary of recent work addressing energy efficient and low-power design within all layers of the wireless network protocol stack.

There is general belief that networks based on wireless technologies have much higher error rates than those based on more traditional technologies such as optical fiber, coaxial cable, or twisted pair wiring. This difference has motivated research on new protocol suites specifically for wireless networks. While the error characteristics of wired networks have been well documented, less experimental data is available for wireless LANs. In this

Mobile nodes of the future will be equiped with multiple network interfaces to take advantage of overlay networks, yet no current mobility systems provide full support for the simultaneous use of multiple interfaces. The need for such support arises when multiple connectivity options are available with different cost, coverage, latency and bandwidth characteristics, and applications want their data to flow over the interface that best matches the characteristics of the data. We present an architecture called Transport Layer Mobility that allows mobile nodes to not only change their point of attachment to the Internet, but also to control which network interfaces are used for the different kinds of data leaving from and arriving at the mobile node. We implement our transport layer mobility scheme using a split-connection proxy architecture and a new technique called TCP Splice that gives split-connection proxy systems the same end-to-end semantics as normal TCP connections.

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.

Due to the availability of a wide variety of wireless access technologies, a mobile host can potentially have subscriptions and access to more than one wireless network at a given time. In this paper, we consider such a multi-homed mobile host, and address the problem of achieving bandwidth aggregation by striping data across the multiple interfaces of the mobile host. We show that both link layer striping approaches and application layer techniques that stripe data across multiple TCP sockets do not achieve the optimal bandwidth aggregation due to a variety of factors specific to wireless networks. We propose an end-to-end transport layer approach called pTCP that effectively performs bandwidth aggregation on multi-homed mobile hosts. We show through simulations that pTCP achieves the desired goals under a variety of network conditions.

Mobile wireless networks pose interesting challenges for routing system design. To produce feasible routes in a mobile wireless network, a routing system must be able to accommodate roving users, changing network topology, and fluctuating link quality. We discuss the impact of node mobility and wireless communication on routing system design, and we survey the set of techniques employed in or proposed for routing in mobile wireless networks.

In this paper, we study the effects of network asymmetry on endto -end TCP performance and suggest techniques to improve it. The networks investigated in this study include a wireless cable modem network and a packet radio network, both of which can form an important part of a mobile ad hoc network. In recent literature (e.g., [18]), asymmetry has been considered in terms of a mismatch in bandwidths in the two directions of a data transfer. We generalize this notion of bandwidth asymmetry to other aspects of asymmetry, such as latency and media-access, and packet error rate, which are common in wide-area wireless networks. Using a combination of experiments on real networks and simulation, we analyze TCP performance in such networks where the throughput achieved is not solely a function of the link and traffic characteristics in the direction of data transfer (the forward direction) , but depends significantly on the reverse direction as well. We focus on bandwidth and latency asymmet...