20190625

Page 1

Pagina 1 di 8 Fundamentals of Communication Networks Prof. G. Maier Exam – 25st June 2019 Surname Name Student ID Total time 2:15 Ex1 (6pt) Ex2 (6pt) Ex3 (6pt) Ex4 (6 pt) Ques (8 pt) 1 - Exercise (6 points) Consider the network below, where links are fiber-optics cables. At time t=0, hosts A, D, F start sending the following sequences of packets (one immediately after the other): - From A, with destinations: B, B, C, B and packet size 1500 kbyte - From D, with destination: C and packet size 2000 kbyte - From F, with destinations: B, B and packet size 1000 kbyte All the nodes R1, R2 and R3 operate in the store-and-forward mode, with FIFO queues. Using a time diagrams, compute the arrival time of each packet to destination. Pagina 2 di 8 Pagina 3 di 8 2 - Exercise (6 points) Consider the network below, in which the cost of each link is reported near the link. 1- Apply the Dijkstra algorithm to compute the shortest-path tree form node It to all the other nodes. Draw the tree on the right of the map and fill in the routing table of It node below 2- Consider the shortest path between node It and node Uk computed in the previous step. Compute the second shortest path between the same nodes which is link-disjoint with the first (write the sequence of nodes and the cost of the path). Then compute the third shortest path link-disjoint with the second and the first and so on, until possible. 3- How many different disjoint paths connect the two nodes Uk and It? How many link failures can be recovered in the worst-case scenario? It Dest. Next hop Cost Pt Sp Fr Uk Ge Ck Gr Pl Ur Sw Pagina 4 di 8 3 - Exercise (6 points) Consider a file transfer from host A to host B over a TCP connection. The size of the file is B = 37.5 kbyte. Given the following assumptions: • Segment and ACK…