Implementation And Performance Evaluation And Also Optimization Of DYMO Protocol Based On Opnet Platform

Wireless network has attracted more and more attention in the field of communication science since 1970s. It can be categorized into two kinds:one is center-controlled network such as cellular network; the other is self-organized wireless network without center such as Ad Hoc network.The Ad Hoc network is receiving increasing attention and application due to its mobility and convenience it can provide to people. But its specificity makes it impossible to adopt the technologies utilized in traditional networks. So some new protocols and technologies need to be developed specially for the Ad Hoc network. The promotion and relevant performance analysis of routing protocols for Ad Hoc network have become a research hotspot in academia.During the study, we find that route discovery mechanism has become steady for on-demand routing protocols, so in this paper, we mainly study the link maintenance mechanism in routing protocol. Only the link maintenance mechanism can help routing protocol sense the variance of network topology, so its performance affect routing protocol's performance directly. It's very important to evaluate its performance. We choose DYMO as Ad Hoc's routing protocol relevant to the link maintenance in the protocol stack. There is no big difference between DYMO and AODV, but DYMO doesn't make a detailed specification about its link maintenance, so we choose DYMO.During the study, we find two shortages about hello mechanism as traditional link maintenance. One is big delay to find broken link; the other one is that hello mechanism often makes wrong judgments if MAC is not well supporting the broadcasting frame. We promote that MAC layer feedback should be the link maintenance mechanism when the network load is light, it can help reduce the delay to sense the broken link and save the packets which shouldn't be dropped; use the uni-cast hello mechanism as the link maintenance mechanism when the network load is heavy, it can help avoid the MAC shortage about broadcasting frame, help routing protocol more accurately sense the connectivity with its neighbor. Both data packet and controlling packet of routing protocol must flow into MAC layer; so many controlling packets may be dropped when congestion appears in MAC layer. This worse the performance of the link maintenance mechanism, and also the routing protocol's performance further. So we suggest that EDCA can be used to transmit the routing protocol's controlling packet more reliably when congestion appears, and the routing protocol can sense the variance of network topology more accurately.