20200123

Page 1

Fundamentals of Communication Networks Prof. A. Pattavina I exam – 23 January 2020 Surname and name: (upper case) Signature: (your readable signature) Matricola ID: Pag. 1/10 1 - Exercise* (6 points) Consider the wired packet switching network shown below. Source H starts transmitting at time t = 0 a sequence of six packets addressed to destinations A, B, C, D, B, D. These packets are denoted, respectively, as A1, B1, C1, D1, B2, D2 . All routers (R1, R2, R3, R4) are store&forward routers and their packet processing time is negligible. Assume that all packets have a fixed size L=12 kbyte. • Draw on a time diagram the sequence of transmissions by the source H and by each router showing the arrival time at each destination • Fill up the table below indicating the initial transmission (tx) time of each packet node by node • Express the time when each packet is completely received at respective destination, indicating such times as TA1, TB1, TC1, TD1, TB2, TD2 (denote by Tx and τx the transmission time and propagation time on link x = 1,2,3,4,5,6,7,8) • Compute numerically TA1, TB1, TC1, TD1, TB2, TD2 and fill up the last column of table below Packet Start tx in H Start tx in R1 Start tx in R2 Start tx in R3 Start tx in R4 End receiving at destination A1 TA1,H= TA1,R1= TA1,R2= TA1,R3= TA1= B1 TB1,H= TB1,R1= TB1,R2= TB1,R3= TB1= C1 TC1,H= TC1,R1= TC1,R2= TC1,R4= TC1= D1 TD1,H= TD1,R1= TD1,R2= TD1,R4= TD1= B2 TB2,H= TB2,R1= TB2,R2= TB2,R3= TB2= D2 TD2,H= TD2,R1= TD2,R2= TD2,R4= TD2= * Fundamentals of Communication Networks Prof. A. Pattavina I exam – 23 January 2020 Pag. 2/10 Fundamentals of Communication Networks Prof. A. Pattavina I exam – 23 January 2020 Pag. 3/10 Fundamentals of Communication Networks Prof. A. Pattavina I exam – 23 January 2020 Pag. 4/10 2 - Exercise (6…