d hoc networks consist of a set of mobile hosts communicating among themselves using wireless links, without the use of any other communication support facilities (e.g., base stations). They are also called mobile radio networks or multihop wireless networks. Two mobile hosts (MHs) are said to be within range and neighbors of each other if each can receive the other's transmission. Every MH behaves in a cooperative fashion by acting as a router, allowing packets destined to other MHs to pass through it.The topology of an ad hoc network changes every time an MH's movement results in the establishment of new wireless links (an MH moves within range of another) or link disconnections (an MH moves out of range of another which was within its range). The rate of topology change is dependent on the extent of mobility and transmission range of the hosts. Routes are heavily dependent on the relative location of MHs. Hence, routes may be repeatedly invalidated in an unpredictable and arbitrary fashion due to the mobility of hosts. The mobility of a single node may affect several routes that pass through it.In this article, we consider the problem of maintaining reliable end-to-end communication in ad hoc networks, similar to that provided by TCP over the Internet. It is desirable to use TCP directly even in ad hoc networks in order to provide seamless portability to applications like file transfer, e-mail, and Web browsers written using standard TCP libraries.Hence, it is of interest to study the behavior of TCP in the context of ad hoc networks and evaluate the effect of dynamic topology on TCP performance. Our studies and simulation results indicate that as a result of frequent and unpredictable route disruptions, TCP's performance is substantially degraded. We propose a feedback mechanism for overcoming this problem. Simulation experiments show that the use of feedback mechanisms along with TCP can result in substantial performance improvements.The rest of the article is organized as follows. We describe existing work in related areas. We describe the ad hoc network model and assumptions. We discuss the behavior of TCP in ad hoc networks and explain the proposed approach for improving TCP performance. The simulation model, experiments, and observations are presented and discussed, followed by conclusions. Related WorkThe dynamic nature of topology in ad hoc networks poses many interesting problems in the domain of routing protocols. As a result, ad hoc networks have been studied extensively in the context of routing (i.e., at the network layer). In these networks, it is necessary to have a routing protocol that:• Quickly provides relatively stable, loop-free routes • Adapts to the mobility of the network Conventional protocols like link state and distance vector do not match these requirements because they do not converge quickly enough or scale well as mobility increases. A number of alternative protocols have been proposed, including a dynamic sequenced distance vector (DSDV) AbstractAd hoc networks are completel...

d hoc networks consist of a set of mobile hosts communicating among themselves using wireless links, without the use of any other communication support facilities (e.g., base stations). They are also called mobile radio networks or multihop wireless networks. Two mobile hosts (MHs) are said to be within range and neighbors of each other if each can receive the other's transmission. Every MH behaves in a cooperative fashion by acting as a router, allowing packets destined to other MHs to pass through it.The topology of an ad hoc network changes every time an MH's movement results in the establishment of new wireless links (an MH moves within range of another) or link disconnections (an MH moves out of range of another which was within its range). The rate of topology change is dependent on the extent of mobility and transmission range of the hosts. Routes are heavily dependent on the relative location of MHs. Hence, routes may be repeatedly invalidated in an unpredictable and arbitrary fashion due to the mobility of hosts. The mobility of a single node may affect several routes that pass through it.In this article, we consider the problem of maintaining reliable end-to-end communication in ad hoc networks, similar to that provided by TCP over the Internet. It is desirable to use TCP directly even in ad hoc networks in order to provide seamless portability to applications like file transfer, e-mail, and Web browsers written using standard TCP libraries.Hence, it is of interest to study the behavior of TCP in the context of ad hoc networks and evaluate the effect of dynamic topology on TCP performance. Our studies and simulation results indicate that as a result of frequent and unpredictable route disruptions, TCP's performance is substantially degraded. We propose a feedback mechanism for overcoming this problem. Simulation experiments show that the use of feedback mechanisms along with TCP can result in substantial performance improvements.The rest of the article is organized as follows. We describe existing work in related areas. We describe the ad hoc network model and assumptions. We discuss the behavior of TCP in ad hoc networks and explain the proposed approach for improving TCP performance. The simulation model, experiments, and observations are presented and discussed, followed by conclusions. Related WorkThe dynamic nature of topology in ad hoc networks poses many interesting problems in the domain of routing protocols. As a result, ad hoc networks have been studied extensively in the context of routing (i.e., at the network layer). In these networks, it is necessary to have a routing protocol that:• Quickly provides relatively stable, loop-free routes • Adapts to the mobility of the network Conventional protocols like link state and distance vector do not match these requirements because they do not converge quickly enough or scale well as mobility increases. A number of alternative protocols have been proposed, including a dynamic sequenced distance vector (DSDV) AbstractAd hoc networks are completel...

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