GATEverse — GATE CSE previous year questions

Consider a simple graph with unit edge costs. Each node in the graph represents a router. Each node maintains a routing table indicating the next hop router to be used to relay a packet to its destination and the cost of the path to the destination through that router. Initially, the routing table is empty. The routing table is synchronously updated as follows. In each updated interval, three tasks are performed.

Continuing from the earlier problem, suppose at some time $t$ , when the costs have stabilized, node $A$ goes down. The cost from node $F$ to node $A$ at time $(t + 100)$ is : $>100$ but finite $\infty$ $3$ $>3$ and $\leq 100$

(A)

A node determines whether its neighbors in the graph are accessible. If so, it sets the tentative cost to each accessible neighbor as $1$ . Otherwise, the cost is set to $∞$ .

(B)

From each accessible neighbor, it gets the costs to relay to other nodes via that neighbor (as the next hop).

(C)

Each node updates its routing table based on the information received in the previous two steps by choosing the minimum cost.