A vector protocol that advertises such costs is also

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Unformatted text preview: cost of the link from the node to the neighbor) known to the recipient, to calculate its own cost to the destination. A vector protocol that advertises such costs is also called a distance-vector protocol.3 Routing protocols in the second category are called link-state protocols. Here, each node advertises information about the link to its current neighbors on all its links, and each recipient re-sends this information on all of its links, flooding the information about the links through the network. Eventually, all nodes know about all the links and nodes in the topology. Then, in the integration step, each node uses an algorithm to compute the minimum-cost path to every destination in the network. We will compare and contrast distance-vector and link-state routing protocols at the end of the next chapter, after we study how they work in detail. For now, keep in mind the following key distinction: in a distance-vector protocol (in fact, in any vector protocol), the route computation is itself distributed, while in a link-state protocol, the route computation process is done independently at each node and the dissemination of the topology of the network is done using distributed flooding. The next two sections discuss the essential details of distance-vector and link-state protocols. In this lecture, we will assume that there are no failures of nodes or links in the network; we will assume that the only changes that can occur in the network are additions of either nodes or links. We will relax this assumption in the next lecture. We will assume that all links in the network are bi-directional and that the costs in each direction are symmetric (i.e., the cost of a link from A to B is the same as the cost of the link from B to A, for any two directly connected nodes A and B ). ￿ 18.4 A Simple Distance-Vector Protocol The best way to understand any routing protocol is in terms of how the two distinctive steps—sending advertisements and integrating advertisements—w...
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