Improving TCP Performance over Ad-hoc Mobile Networks
Xuanming Dong, Duke Lee, Jin Wang · 2000
TCP connections in Ad-hoc mobile networks are plagued by problems such as high bit error rates, frequent route changes, and temporary network partitions, etc. The throughput of TCP over such connections is extremely poor because TCP misinterprets the packet loss or delay as congestion and invokes congestion control. In this paper we explore to use ERN (Explicit Route Notification) mechanism to inform the TCP sources when the packet can’t be delivered due to route re-computation or temporary network partitions. Therefore TCP source can distinguish between temporary route failure and real network congestion so that TCP source can handle them independently to avoid throttling the transmission rate due to TCP’s implicit assumption that most packet losses are due to congestion. In our scheme, TCP source has two states: the normal state and the frozen state. When TCP source receives the ERFN (Explicit Route Failure Notification) messages from the routers, it switches to the frozen state from the normal state by freezing timers and stops sending further packets. Once the route is recovered or the temporary partition disappears, the router informs the TCP source by sending the ERRN (Explicit Route Recovery Notification) messages, which cause TCP source return to the normal state and behave as a usual TCP source. The routers can buffer packets temporarily when sending out the ERFN messages and forward buffered packets when sending out the ERRN messages. We have implemented the ERN mechanism in ns-2 and done some preliminary experiments. In this report, we present several simulation results and compared them with those obtained using TCP Reno.