This question explores how to set the (configurable) link weights in link-state

Question

This question explores how to set the (configurable) link weights in link-state routing protocols like OSPF inside a single Autonomous System (AS) to achieve AS-wide goals. How should the network operators set the link weights if their goal is to minimize the number of hops each packet traverses to reach its destination? How should the operators set the link weights to minimize the end-to-end delay the traffic experiences? Assume the network is lightly loaded, so queuing delay is insignificant. In the picture below, the nodes are routers, the edges are links, and the integers correspond to the link weight on each direction of the link. (That is, the link a-b and the link b-a both have weight 10.) Put arrows on the edges to show the shortest path from every node to the destination node d. That is, show the "sink tree" leading to node d. Suppose the link f-e is overloaded with traffic. Identify a single weight change (on just one link) that would divert traffic from source f to destination d away from the f-e edge without affecting the path between any other source-destination pairs. Avoid any reliance on how routers choose between multiple paths with the same (smallest) cost.

Explanation / Answer

a) the logic is like the weight for all the link is set to the same val for eg put one

b) as the queuing delay is minimal the the only delay is propogtion delay. in that case set the weight of each link to be kept propotional to its length.

c) node a and g taking direct path to d while other nodes first try to reach a or g to reach d so other{b,e,h,c,f,i} will take left arrow .

a< - b< - c

| | |

v v v

d< - e < - f

/ | |

| v v

g< - h < -i

a and g are the adjacent node to d but after that the less weighted path is { i-h-g-d}

d) the link (h--i) changed to 2 so as for now the cost for path { f-i-h-g-d} reduced from 28 to 21 which is less as compared to the link{f-e-d}

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