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...
View Full Document
- Fall '13