01-07-2013, 04:15 PM
supporting efficient and scalable multicasting over mobile
supporting efficient.doc (Size: 41 KB / Downloads: 13)
INTRODUCTION
Conventional MANET multicast protocols can be ascribed into two main categories, tree-based and mesh based. However, due to the constant movement as well as frequent network joining and leaving from individual nodes, it is very difficult to maintain the tree structure using these conventional tree-based protocols (e.g., MAODV, AMRIS, MZRP, and MZR). The mesh-based protocols (e.g., FGMP, Core-Assisted Mesh protocol, ODMR) are proposed to enhance the robustness with the use of redundant paths between the source and the destination pairs.
Conventional multicast protocols generally do not have good scalability due to the overhead incurred for route searching, group membership management, and creation and maintenance of the tree/mesh structure over the dynamic MANET. For MANET unicast routing, geographic routing protocols have been proposed in recent years for more scalable and robust packet transmissions. The existing geographic routing protocols generally assume mobile nodes are aware of their own positions through certain positioning system, and a source can obtain the destination position through some type of location service an intermediate node makes its forwarding decisions based on the destination position inserted in the packet header by the source and the positions of its one-hop neighbors learned from the periodic beaconing of the neighbors. By default, the packets are greedily forwarded to the neighbor that allows for the greatest geographic progress to the destination. When no such a neighbor exists, perimeter forwarding is used to recover from the local void, where a packet traverses the face of the planarized local topology subgraph by applying the right-hand rule until the greedy forwarding can be resumed. Similarly, to reduce the topology maintenance overhead and support more reliable multicasting, an option is to make use of the position information to guide multicast routing. However, there are many challenges in implementing an efficient and scalable geographic multicast scheme in MANET. For example, in unicast geographic routing, the destination position is carried in the packet header to guide the packet forwarding, while in multicast routing, the destination is a group of members. A straight-forward way to extend the geography-based transmission from unicast to multicast is to put the addresses and positions of all the members into the packet header, however, the header overhead will increase significantly as the group size increases, which constrains the application of geographic multicasting only to a small group. Besides requiring efficient packet forwarding, a scalable geographic multicast protocol also needs to efficiently
manage the membership of a possibly large group, obtain the positions of the members and build routing paths to reach the members distributed in a possibly large network terrain. The existing small-group-based geographic multicast protocols normally address only part of these problems.