A Study Of Active Network Based Stream Media Multicast Congestion Control Algorithm

Internet has been being in explosive development in the recent years, especially due to the use of optical fibles as a commom way in telecommunication field.Many new applications,especially large-scale multimedia systems like distant learning applications ,which are mostly UDP based ,are being more widely deloyed. The congestion control for these application has become one of the most important issues in network researchs so that the fairness and stability of future network could be ensured.Although classic TCP congestion control algorithm plays an important role in the current lnternet, it is not suitable for the IP multicast for stream media. so it needs a new multicast congestion control mechanism for a reliable stream-media multicast.Due to it's own features, stream media applications require a raletively stable rate and can't tolerate a high delay.Congestion control in stream media applications has it's own challenge.Nevertheless fairness and extendiblity remain multicast's main challenges.TFMCC algorithm, which proposed the equation of TCP average rate and a new rate based control strategy, provides a new useful approach but with weakness to congestion control for reliable multicast . Active network provides a programmable network interface in network nodes. Active networks not only have the basic capability of forward packets toward their destination as of a traditional packet network, but alse have the capability to support dynamic modification of the network's behavior as seen by user. A novel scalable architecture of active network in network simulation environment is given an implementd. On the base of analyzing Active network and TFMCC scheme, this dissertation provides a multicast congestion algorithm on active network(ARMCC). It realizes the idea of TFMCC based on the combination of TFMCC's rate control mentality and the programmable mechanism of active network, Our algorithm includes five mechanisms: hierarchical RTT measurement, congestion detection, rate adjusting, and congestion smoothing buffer management. With flexible use of the resources in active router, ARMCC can not only let multicast flows have an adjustable share of bandwidth of bottleneck links with TCP flows, achieve inter-protocol fairness, but also limit the effect of congestion on a specific link to a small region, achieve intra- protocol fairness. It solves the drop-to-zero problem, and has good scalability. In addition, ARMCC adopts TCP throughput formula to provide smooth transmit rate, and make the rate in network never under minimum rate, which guarantees the efficiency of streaming media.This dissertation designs and analyse the algorithm, and implements it in OPNET modeling language. The experiment results reval thar this algorithm is an effectivemulticast congestion algorithm and has some practical use.