Different Issues and Survey of Proposed Solutions in TCP over Wireless Environments

Abstract

Abstract— Computer networks have experienced an explosive growth over the past few years, which has lead to some severe congestion problems. Reliable protocols like TCP works well in wired networks where loss occurs mostly because of congestion. However, in wireless networks, loss occurs because of bit rates and handoffs too. TCP responds all losses by congestion control and avoidance algorithms, which results in degradation of TCP’s End-To-End performance in wireless networks. This paper discusses different issues and problems regarding use of TCP in wireless networks and provides comprehensive survey of various schemes to improve performance of TCP in Wireless Networks. Keywords—TCP, Mobile-IP, Wireless networks, Protocol design. I. INTRODUCTION Due to rapid advances in the area of wireless communications and the popularity of the Internet, the provision of packet data services for applications like e-mail, web browsing, mobile computing etc. over wireless is gaining importance. The TCP/IP protocol suites have number of layers, of which transport layer is used widely for mobility. It uses protocols like TCP and UDP for transferring data. While coming towards wireless environment, we must understand what wireless environment is first. Wireless environment can be broadly distinguished in three types: Cellular networks, Ad-hoc networks and Satellite networks. In Cellular Networks a mobile host is connected to the fixed network with the help of the Base Station. This is the most common form of Wireless Network currently in use. Mobile devices like cell phones, laptops use this network. Most of the proposed solutions to TCP use this model. All service providers are on the fixed network and hence we have to address the problem of wireless networks only at one end point. Ad – Hoc Networks are formed by mobile hosts which are connected to each other within a radio distance. This kind of a model is not well deployed and very few solutions have been proposed to this model. Satellite Networks are those where a satellite link is in between the sender and the receiver. These have very high BERs (Bit Error Rates) and high latency because the Satellite are at a great distance from the surface. Now going towards our main concept, Transmission Control Protocol (TCP) [1] is one of the important standards in the internet world and also a very vital element in internet protocol suite. It provides a connection oriented service with reliable data transfer over the unreliable underlying protocols. It uses sequence numbering and timers to ensure reliable transfer of packets. TCP's flow control increases the data sending rate until there are signs of congestion in the network. The basis of TCP congestion control lies in the following algorithms: slow start, congestion, avoidance, fast retransmit and fast recovery [2]. In the following we first outline the different issues of TCP in wireless networks. Then the main problem regarding TCP. Then we summarize some proposed solutions with their strengths and weaknesses. II. I