The Design And Realization Of An Opportunistic Routing Mechanism For Wireless Channel Instability

The subject comes from Ministry of Education project of Broadband Communication Network Laboratory:The Research and Realization of Adhoc Network Test-bed. The routing mechanism proposed by this paper is for Adhoc network. Adhoc is a kind of wireless network. It is multi-hop, temporary, and no center. This kind of mobile network could be quickly established at any time and any place. It does not rely on the support of the existing fixed network facilities.Routing Protocol is one of the key technologies that affect the performance of Adhoc network. Adhoc network typically uses routing techniques similar to those in wired networks. After deep research, it is realized that this kind of routing techniques could not adapt to the volatility of wireless channel and the dynamics of topology. Random routing proposed first by MIT is proved to be an effective solution for this problem. Research organizations proposed all kinds of opportunistic routing mechanism. Now most research of opportunistic routing protocol remains in the stage of simulation and could not support multi-streaming in the network.The core idea of opportunistic routing protocol is that the source node does not choose the next hop before sending packet, instead the source node broadcasts the packet, and chooses the best next hop dynamically among nodes which really receive the packet. The process continues until the destination. This paper proposed a new opportunistic routing mechanism. The mechanism uses RREQ message and RREP message to establish forward list. Only nodes among forward list could forward the packet. The nodes in the list are set priority by their hop to destination. The mechanism chooses the best node to forward packet. The forward list is established and maintained by source node. The intermediate nodes do not have to maintain routing information." In comparison with other opportunistic routing mechanisms, the new mechanism proposed could support multi-stream in the network and the overhead of creating forward list is much lower.The main part of this paper is the realization of opportunistic routing mechanism on Linux platform as a loadable kernel module. The implementation of the protocol is divided into two parts:system interaction and protocol algorithm. The system interaction part takes full advantage of the open interface of Linux network stack. The realization involves the registration of handlers of network layer and transport layer, in addition, the mechanism registers a new virtual NIC. The protocol algorism part analyzed the operation of RREQ module, RREP module and packet-forwarding module, and then gave detailed code process of different modules. In the end, the paper compared the performances of opportunistic routing and AODV from time-delay and packet delivery.