Improving TCP performance during soft vertical handoff

With the help of Mobile IP/IPv6, on-going TCP sessions can remain active when the mobile node hands over from one network to another. In particular, in a soft vertical handoff, packet loss due to the switching of networks can be avoided. However, TCP still faces several performance degradation issues due to the change of network bandwidth and propagation delay. During vertical handoff, some undesirable phenomenon may erroneously trigger TCP congestion control operations and thus degrade the TCP performance. In this paper, we study the TCP behaviors during soft vertical handoff from fast link to slow link. In particular, we focus on TCP timeout problem caused by increased network round-trip time, and propose three schemes (fast response, slow response and ACK delaying) to solve this problem. These schemes require only minor modifications on network layer of the end hosts, without any change on TCP and intermediate network routers. Simulation results show that these schemes can effectively improve the TCP performance during soft vertical handoff.