Question
Consider the network fragment shown below. x has only two attached neigh- bors, w and y. w has a minimum-cost path to destination u (not shown) of 5, and y has a minimum-cost path to u of 6. The complete paths from w and y to u (and between w and y) are not shown. All link costs in the network have strictly positive integer values.
a. Give x’s distance vector for destinations w, y, and u.
b. Give a link-cost change for either c(x,w) or c(x,y) such that x will inform its neighbors of a new minimum-cost path to u as a result of executing the distance-vector algorithm.
c. Give a link-cost change for either c(x,w) or c(x,y) such that x will not inform its neighbors of a new minimum-cost path to u as a result of executing the distance-vector algorithm.
Answer
a)
Consider the diagram:
Minimum cost path from node w to node u= 5.
Minimum cost path from node w to node y =6.
Distance-vectors from node x are as follows:
Vx(w)=2
Vx(y)=5
Vx(u)=
Considering the neighbors of node y and node w from x in the first iteration completed
Vx(w)=2
Vx(y)=4
Vx(u)=7
b)
Give a link-cost change for either c(x,w) or c(x,y) such that x will inform its neighbors of a new minimum-cost path to u.
The result of executing the distance-vector algorithm is node x again informs its neighbors of the new cost.
c)
Give a link-cost change for either c(x,w) or c(x,y) such that x will not inform its neighbors of a new minimum-cost path to u.
The result of executing the distance-vector algorithm is not cause x to inform its neighbors of a new minimum-cost path to u.