Improving TCP Performance by Packet Buffering in Mobile IP Based Networks

It is well–known that TCP often experiences severe performance degradation in mobile networks since due to host mobility, packet losses not related to network congestion occur frequently. In this paper, we propose a buffering of packets at a base station to resolve such a problem. Our method can be used without sacrificing the scalability in Mobile IP based networks. For this purpose, we first investigate the performance of TCP without considering packet buffering through simulation experiments. Our results show that in most cases, the smooth handoff by the route optimization extension of the Mobile IP standard cannot prevent degradation of TCP performance in evens of handoffs, although it was originally intended to reduce the number of packets dropped during the handoff. It is also shown that in utilizing the route optimization extension, the TCP performance sometimes becomes worse even than the case of the base Mobile IP, if its smooth handoff fails to avoid losses of four or more packets during the handoff. Such results indicate that for TCP, the smooth handoff is not useful unless the route optimization extension supports a buffering method, which makes handoffs be transparent to transport layer protocols by recovering lost packets during the handoff. We next investigate the impacts of packet buffering on TCP performance. We modify the route optimization extension in order to support packet buffering at the base station, which only requires minor changes. Finally, we discuss some problems occurring when recovering the packets dropped during the handoff by the buffering method, and propose our solution.