Reliable Multicast Protocol In Wireless Ad Hoc Networks Optimal Caching Strategy

Ad Hoc Networks,which are characterized by complete wireless links,mobility and non-infrastructure, can be deployed under any environment and thus provide wireless communications. With the development of Ad Hoc networks, the group-oriented applications become more attractive. Further more, the applications such as file transmission, sharing of important and confidential information in battlefields, demand the Ad Hoc network provides reliable multicast guarantees.Due to the characteristics of Ad Hoc networks, reliable multicast in Ad Hoc network is difficult with a number of problems such as NAK implosion, distributed loss recovery, retransmission scoping, etc. And in the Ad Hoc network, links are different since some links are reliable while some are relatively unreliable. Reliable Multicast in Ad Hoc networks needs to deal with these problems. Caching data packets at some designated nodes such as repair servers for future possible loss recovery can efficiently decreases the sender's load and the effect of NAK explosion, which is especially important in the resource-constrained wireless networks. How to utilize the limited resources efficiently for packet loss recovery is an important issue. A"smarter"loss recovery scheme, which can manage packets according to the Ad Hoc networks'characters, could provide a better solution for reliable multicast.Buffer management is an important issue which affects the loss recovery performance. The recent design of reliable multicast protocols, including ReACT, does not address this issue. There is also only little previous research work on it. In this paper, we study the buffer management to improve the performance of loss recovery in several reliable multicast protocols. First, we formulate the caching policy design as an optimization problem, and define Caching Efficiency as the measurement of caching policy. Based on that, we propose a new scheme for buffer management——OCT (Optimal Caching Tine) caching policy, and define an OCT algorithm to adaptively configure the optimal caching time to perform the OCT caching policy. To the best of our knowledge, there are few existing buffer management schemes for reliable multicast and it is evident that most proposed reliable multicast protocols including ReACT use simple FIFO discipline. Therefore, we compare our OCT with existing caching policies by several kinds of analysis. NS2 network simulator is employed to study the performance of the proposed scheme. Numerical results reveal that OCT caching policy gives the significant performance improvement in terms of loss recovery latency, bandwidth consumption and network throughput even under heavy traffic loads.