tailieunhanh - AD HOC NETWORKS Technologies and Protocols phần 5

đó là mong muốn rằng một giao thức định tuyến được năng lượng hiệu quả nhất. Điều này cũng cung cấp cũng là một lý do tại sao các chi phí phải được giữ ở mức thấp. Vì vậy, các giao thức định tuyến phải đáp ứng các mục tiêu mâu thuẫn nhau của thích ứng năng động và chi phí thấp để cung cấp hiệu suất tổng thể tốt | Introduction 93 The mobility of the nodes creates a continuously changing topology for communication. Routing paths break and new ones are formed dynamically. Unlike the wired network wireless medium is a broadcast medium all nodes in the transmission range of a node can hear the packets simultaneously. In light of the above differences the issues and challenges for intercommunication in MANETs are more complex than their wired counterpart. IP multicasting was first proposed over a decade ago 1 as an extension to Internet architecture to support multiple clients at network layer. The fundamental motivation behind IP multicasting is to save network and bandwidth resource via transmitting a single copy of data to reach multiple receivers simultaneously. A basic principle for the forwarding tree is to branch as close to the receivers as possible. In ad hoc networks we want to adhere to this requirement as closely as possible because of the severe bandwidth limitations in ad hoc networking environments. Similar to Internet multicasting it is necessary to deal with dynamic memberships in multicast groups in ad hoc networks. In both Internet and ad hoc multicasting dynamic membership refers to the fact that individual clients may join and leave multicasting sessions dynamically. As a result a multicast protocol needs to define operations of member join and leave and how to recover from routing failure. The data forwarding path is constructed either as a tree or a mesh. What makes ad hoc multicasting distinguished from Internet multicasting is that mobile nodes could move around freely and rapidly. In other words we have to deal with high network dynamics due to node mobility which makes ad hoc multicasting even more challenging. Ad hoc multicasting protocols in existing literature have either evolved from the Internet multicast protocol or designed specifically for ad hoc networks. Most of these protocols attempt to adapt to the network dynamics in ad hoc networks. The .