Skip to Main Content
Cache and forward (CNF) Architecture is a novel architecture aimed at delivering content efficiently to potentially large number of intermittently connected mobile hosts. It uses a reliable hop-by-hop transport mechanism where in-network storage is leveraged to store the entire file in each node, before forwarding it towards the destination(s). Links between nodes may be wired, or wireless, 802.11 a/b/g, cellular, or satellite, or some other upcoming wired/wireless technology. A key aspect in the CNF architecture is to choose the link-layer protocol with parameters such that it optimizes the performance of the link between two CNF nodes. In this paper we propose cross-layer aware transport protocol (CLAP) as a potential candidate for a reliable link-layer protocol between two CNF nodes connected by 802.11 a/b/g link. Leveraging upon MAC layer status information, CLAP quickly adapts its flow control rate to bandwidth fluctuations and maximizes link utilization efficiency. Due to the self-interference problem in wireless links, where ACK packets corresponding to a given flow interfere with the DATA packets of the same flow, CLAP's error control algorithm is based on aggregate negative acknowledgements (NACKs) which reduce the reverse traffic and hence the interference with the data traffic. Since CLAP performs transport layer functionality, we compare it with TCP-SACK -a popular variation of TCP. CLAP significantly outperforms TCP-SACK in both noise-free and noise-prone wireless environments, with throughput gains upward of 150%. For multiple flows, CLAP leverages the fairness characteristics of the underlying MAC layer to achieve fair bandwidth sharing among flows.