Low-latency Routing for Short-Lived TCP Connections in Wireless Ad Hoc Networks

A wireless ad hoc network does not require wired infrastructure or network management terminal. That is, it is self-organized only with wireless terminals that exchange network information, maintain routes, and construct a multi-hop distributed network. In the wireless ad hoc network, there is no need for wired infrastructure or network management terminal. Therefore, quickly and easily we can build a large-scale network with flexibility in adding and removing terminals. Such a wireless infrastructure is applicable to, e.g., distributed computing, disaster recovery, and military operation. A sensor network system, which collects information from many terminals, is another good example of the ad hoc network. In the past, many studies have been dedicated to analyze characteristics or to propose new routing methods of the wireless ad hoc networks. See, e.g., [1-3]. With expectation that it is integrated with wired networks by using TCP, the performance of TCP over ad hoc networks has been studied in [4-8]. However, most of those studies assume that the TCP connection is persistent; i.e., it has an infinite amount of data to transmit, and then they examine the steady-state throughput values. It is apparently inadequate because many TCP connections are short-lived. For example, it is reported in [9] that the average size of Web documents at several Web servers is about 10 [KBytes]. Especially, in the sensor network, the amount of data on each connection is small, and major of the TCP connections would be short-lived. Since TCP is end-to-end communication protocol including wireless and wired terminals, its modification dedicated to the sensor network is not adequate for protocol migration. Instead, we should consider a new routing protocol in the ad hoc network suitable for the short-lived TCP connections. To improve the performance of short-lived connections, we need to tackle the following problems, which are not resolved in the existing routing protocols; • large overhead of exchanging the routing table • large latency for an initial route search process • large latency for another route search in the case of link disconnection If we assume TCP is persistent as in the existing routing protocols, the above problems do not affect the performance even in high-mobility and high traffic load environment. However, in actual TCP is never persistent, and most connections are short-lived.