Hierarchical cache design for enhancing TCP over heterogeneous networks with wired and wireless links

TCP is a reliable transport protocol tuned to perform well in traditional networks made up of links with low bit-error rates. Networks with higher bit-error rates, such as those with wireless links and mobile hosts, violate many of the assumptions made by the transmission control protocol (TCP), causing degraded end-to-end performance. We propose a two-layer hierarchical cache architecture for enhancing TCP performance over heterogeneous networks with both wired and wireless links. A new network-layer protocol, called new snoop (NS), is designed. The main idea is to cache the unacknowledged packets at both the mobile switch center (MSC) and base station (BS), to form a two-layer cache hierarchy. If a packet is lost due to transmission errors in the wireless link, the BS takes the responsibility to recover the loss. When a handoff occurs, the packets cached at the MSC can help to minimize the latency of retransmissions due to temporal disconnection. NS can preserve the end-to-end TCP semantics and is compatible with existing TCP applications. Its implementation only requires code modification at the BS and MSC. Simulation results show that NS is significantly more robust in dealing with unreliable wireless links and handoffs as compared with the original snoop scheme, as well as some other existing TCP enhancements.