Research On QoS And Congestion Control Technology Over IP Multicast Networks

Recently, more attentions are paid to QoS of IP multicast routing. IP Multicast routing protocols use multicast trees to deliver packets, such as source trees or share trees, which depend on how a multicast tree is constructed. It has been shown that IP multicast protocols tend to construct a single minimum spanning tree for a multicast source (i.e., group), resulting in too heavy load on some IP multicast network links, too light load on other links and bottleneck effects occurring frequently. This affects and limits the network performance severely where only a few internal nodes supply multicast traffic. This leads to an inefficient utilization of network resources especially when there co-exists multiple multicast sources in the network, where bottleneck effects may occur frequently.Unfortunately, most of the researches related to multicast focused on single multicast group problems. Some greedy algorithms designed for making one of the multicast groups get its high throughput while others could not. Some algorithms were proposed to distribute multicast traffic for a session over multiple multicast trees. However, this scheme suffers from too much cost. Some other researches proposed multicast scheduling mechanism based on copy numbers of multicast packets, which can not solve the problems of load balance and congestion control. In this paper, we propose a new network utilization algorithm, called Load Distribution Algorithm (LDA), to improve the efficiency of QoS, network utilization and congestion control by balancing the load of multicast traffic when there co-exist multiple multicast sources.The LDA algorithm achieves efficient utilization of network resources through splitting the multicast traffic on candidate paths. The proposed LDA mainly consists two parts:Selecting Candidate Path (SCP) and Multicast Scheduling (MS). The LDA algorithm tends to use selecting candidate path based on ant colony algorithm and multicast scheduling to distribute the contention multicast packets onto their corresponding candidate path. At the start, all the nodes in IP multicast networks run LDA to fulfill routing based on ant colony algorithm. When there are input multicast packets contending with other input multicast packets, and in this case the network resource is limited, such as bandwidth, network storage space, the multicast node will run the LDA to route some multicast services (i.e., ones are served to less users) onto candidate path. As a result, more internal nodes are involved in multicasting and achieve balancing the network load.Simulation results show that the proposed LDA algorithm performs well and multicast protocol with LDA is able to provide better multicast services than that without LDA, esp. in the case that multicast networks have limited network resources. In other words, multicast protocol with LDA can significantly reduce the average multicast packet delay, and at the same time, intend to avoid the network congestion and improve network utilization.