Reliable Multicast In Manets In Local Recovery And Congestion Control Design

Wireless communications environment's characteristics pose a number of constraints to providing multicast service in MANETs. How to ensure the reliability of multicast in MANETs, reduce loss recovery latency and improve the network throughput is the key issue to address for designing a reliable multicast protocol.In this paper, we analyze the effect of using reliability control and congestion control mechanisms independently and the necessity of jointly considering the two mechanisms. We first use two typical multicast transport protocols, SRM and CALM, to investigate how the loss recovery and congestion control mechanisms impact the multicast performance in MANETs, and summarize their advantage and shortage. Based on the insights from our analysis, we propose a new multicast transport model which integrates local loss recovery and congestion control mechanisms. This design avoids the unnecessary reduction of data transmission rate of the source and simultaneously prevents the congestion from getting worse. Focuing on addressing the key issues of our protocol, this thesis proposes the solution in detail which includes the idea on reducing redundancy repair packet while reducing the number of retransmissions. Furthermore we present logarithm congestion control algorithm to adjust data transfer rate during the congestion control phase.Based on the principle of joint design, we design a Reliable Multicast protocol with Joint Local Recovery and Congestion Control, (ReMLoC). The proposed protocol is based on Tree-structured multicast. We implement the proposed local recovery and congestion control mechanisms on ReMLoC and elaborate the processing procedure of the control packets on multicasting nodes and the change of packet header information. Both local recovery mechanism and congestion control mechanism are effectively combined in the transmission of all packets in ReMLoC.At last, we use ns2 simulation experiments to evaluate the performance of ReMLoC. The implementation structure of ns2 is introduced and the key issues of implementing ReMLoC in ns2, such as the design of packets and the processing procedure at sender and receiver etc., are described in detail. The numerical results show that the performance of ReMLoC can be significantly improved in terms of transmission reliability, decrease loss recovery delay and have good TCP friendliness as well. The results also demonstrate the effectiveness of the joint design to improve network performance of multicast in MANETs.