Performance evaluation of the cache and forward link layer protocol in multihop wireless subnetworks

Cache aNd Forward (CNF) is a clean-slate protocol architecture for content delivery services in the future Internet. CNF is based on the concept of store-and-forward routers with large storage, providing for opportunistic delivery to occasionally disconnected mobile users and for in-network caching of content. This thesis presents the design and evaluation of a reliable link layer protocol for CNF in context of a multi-hop wireless access network scenario. The design aims to deliver files efficiently on a hop-by-hop basis as opposed to an end-to-end approach employed by TCP/IP. CNF leverages in-network storage to store an entire file before forwarding the file to the next node. If a next hop is not currently available or has low transmission quality, files may be stored at each CNF router along the path towards the destination. In addition to the link layer protocol, end-to-end transport in CNF involves packet scheduling and routing at each network node based on cross-layer observation of link speed, MAC congestion, path length, etc. An ns-2 simulation model has been developed for a multi-hop 802.11 access network with CNF routers and a reliable link layer protocol. Baseline results for first-come-first-serve (FCFS) scheduling and shortest path routing show significant capacity gains for CNF relative to TCP for a variety of network topologies and channel models. For example, for a 49 node network with a grid topology, maximum achievable throughput with CNF was found to be 12.5 Mbps as compared to 3.9 Mbps for TCP for a scenario in which the radio links experience short-term outages with a 5% duty cycle. Preliminary results showing the value of simple cross-layer scheduling in CNF are also given in the conclusion.M.S.Includes bibliographical references (p. 48-49)