Performance evaluation of the cache and forward routing protocol in multihop wireless subnetworks.

摘要

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, opportunistic delivery to occasionally disconnected mobile users and in-network caching of content. The CNF architecture uses a storage-aware routing protocol (which can choose to store rather than forward data), along with a reliable hop-by-hop transport protocol in place of end-to-end TCP for reliable delivery of media files. This thesis presents the design and experimental evaluation of the routing protocol for CNF in context of a multihop wireless access network scenario. The protocol is designed to transmit files only when the end-to-end path quality is considered to be acceptably high. The aim here is to optimize a social metric such as the overall network throughput through opportunistic transmission during periods of good path quality. If the routed path is determined to be temporarily degraded, either due to poor channel conditions or mobility, the protocol may decide to store the file. This decision is based on a two-dimensional routing metric which considers the value of both short-term and long-term path metrics such as ETT (expected transmission time) to determine whether to forward or store. In addition to path quality, storage capacity in the downstream routers to the destination is also considered while making the store or forward decision. The CNF protocol stack over multihop 802.11 access networks with CNF routers has been implemented as a real-time proof-of-concept prototype on the ORBIT testbed. Baseline results for the storage aware routing with hop-by-hop transport show significant throughput gains for the CNF stack over the TCP/IP stack for a variety of topologies and network conditions. For example, for a 5-node multihop topology under varying loss conditions, the throughput achieved by CNF is 2X that of TCP. Moreover, as the loss conditions worsen, TCP tends to fail completely, while a graceful degradation of the CNF protocol stack is observed.