41 distance vector protocol advertisements the

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ork. In this section, we explain these two steps for a simple distance-vector protocol that achieves minimum-cost routing. ￿ 18.4.1 Distance-vector Protocol Advertisements The advertisement in a distance-vector protocol is simple, consisting of a set of tuples as shown below: [(dest1, cost1), (dest2, cost2), (dest3, cost3), ...] Here, each “dest” is the address of a destination known to the node, and the corresponding “cost” is the cost of the current best path known to the node. Figure 18-3 shows an example of a network topology with the distance-vector advertisements sent by each node in steady state, after all the nodes have computed their routing tables. During the 3 The actual costs may have nothing to do with physical distance, and the costs need not satisfy the triangle inequality. The reason for using the term “distance-vector” rather than “cost-vector” is historic. 7 SECTION 18.4. A SIMPLE DISTANCE-VECTOR PROTOCOL ,-!1201&quot;-\$1*01&quot;-%1/01&quot;-&amp;.'(01-#.604&quot; !&quot; '(&quot; ,-!1601&quot;-\$1(01&quot;-%1'01&quot;-&amp;.)01-#.204&quot; #&quot; )&quot; *&quot; ,-!1'(01&quot;&quot; -\$1501&quot;&quot; -%1301&quot;&quot; -&amp;1201&quot;&quot; -#1)04&quot;&quot; '&quot; &amp;&quot; *&quot; \$&quot; ,-!1*01&quot;-\$1201&quot;-%1+01&quot;&quot; -&amp;1501&quot;-#1(04&quot;&quot; +&quot; %&quot; ,-!./01&quot;-\$.+01&quot;-%.201&quot;-&amp;.301&quot;-#.'04&quot;&quot; Figure 18-3: In steady state, each node in the the topology in this picture sends out the distance-vector advertisements shown near the node,along each link at the node. process of computing the tables, each node advertises its current routing table (i.e., the destination and cost ﬁelds from the table), allowing the neighbors to make changes to their tables and advertise updated information. What does a node do with these advertised costs? The answer lies in how the advertisements from all the neighbors are integrated by a node to produce its routing table. ￿ 18.4.2 Distance-Vector Protocol: Integration Step The key idea in the integration step uses an old ob...
View Full Document

Ask a homework question - tutors are online