3 hybrid routing this method combines the first two

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Unformatted text preview: tion node because the time taken for each packet depends on the route chosen for that packet, along the with volume of data being transferred along that route. ROUTING TECHNIQUES When multiple paths exist between the source and destination nodes of a packet, any one of the paths may be used to transfer the packet. For example, in the network configuration of Figure 17.17, there are two paths between nodes A and B: 1-5-4 and 1-2-3-4 and any one of the two may be used to transmit a packet from node A to B. The selection of the actual path to be used for transmitting a packet is determined by the routing technique used. An efficient routing technique is crucial to the overall performance of the network. A good routing algorithm should make routing decisions as fast as possible and should be easily implementable in hardware. Furthermore, the decision process usually should not require global state information of the network because such informal gathering is a difficult task and creates additional traffic in the network. Routing algorithms are usually classified based on the following two attributes: 1. Place where routing decisions are made, and 2. Time constant of the information upon which the routing decisions are based. Note that routing techniques are not needed in LANs (described later in this chapter) because the sender of a message simply puts the message on the communication channel and the receiver takes it off from the channel. There is no need to decide the path to be used for transmitting the message from the sender to the receiver. Place Where Routing Decisions are Made Based on this attribute, routing algorithms may be classified into the following three types [Reprinted, with permission, from the book titled Distributed Operating Systems: Concepts and Design by Pradeep K. Sinhi ©1997 IEEE]: 1. Source routing. In this method, the source node selects the entire path before sending the packet. That is, all intermediate nodes via which the packet will be transferred to its destination are decided at the source node of the packet, and this routing information is included along with the packet. The method requires that t...
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