Routing in Ad Hoc Networks for Processing Many Short-lived TCP Connections

Ad hoc wireless networks are self-organized networks built with wireless terminals, which communicate with each other and exchange the network information. They can also relay data packets for another terminal to construct a wide area multi-hop wireless network. The ad hoc networks need neither a wired backbone network nor a base station. As a result, network installation, expansion and removal can be performed easily and quickly. Such a wireless infrastructure covers a wide range of applications, e.g., distributed computing systems, disaster recovery networks, and sensor networks. Accordingly, many studies have been dedicated to analyze its characteristics and/or propose new routing methods (see, e.g., [1]). Some other studies have considered the use of TCP over ad hoc networks (e.g., [2, 3]). However, most of them 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 [4] that the average size of Web documents at several Web servers is about 10 [KBytes]. Furthermore, 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 the TCP connection is persistent, the above problems do not affect the performance even in highmobility and high traffic load environment. In this paper, we propose a new routing protocol that resolves the above problems and achieves low latency for the short-lived connections. We call it as the Low-latency Hybrid Routing (LHR) protocol that combines the on-demand route search and the proactive route maintenance. LHR adopts a quick route re-search method against a link disconnection. This is an advantage of LHR over the existing proactive and on-demand hybrid routing like ADV [5]. As a result LHR can process more TCP connections within a given time period.