Handoff and System Support for Indirect TCP/IP

Over the past few years, Transmission Control Protocol (TCP) has become the most widely used transport layer protocol on the Internet. TCP performs poorly however, if one of the communicating hosts is a mobile wireless computer . One way to address this performance problem is to modify TCP to make it aware of host mobility. Such an approach is infeasible because of the sheer number of hosts on the Internet using TCP. Another way is to build a separate transport layer protocol for mobile hosts but this raises interoperability problems with the existing stationary hosts.

An indirect transport layer protocol such as I-TCP allows using a separate transport protocol for the wireless link between a mobile host and its Mobile Support Router (MSR) without causing interoperability problems with the fixed network. Experiments with I-TCP have shown significant improvement in throughput over regular TCP . Use of indirect protocols requires additional functionality at the MSRs. In this paper we describe the implementation of such functionality for I-TCP. We also present measurements for the time needed for handoffs in case a mobile host with an active connection switches cells.