# hw1 - EE 284 F Tobagi Autumn 2010-2011 EE284 Homework...

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EE 284 F. Tobagi Autumn 2010-2011 EE284 Homework Assignment No. 1 Topic: Switching Techniques, Network Topologies Handed out: September 21, 2010 Due: September 30, 2010 in class (Previously September 28 but now extended by 2 days) Total Points: 45 ALL WORK MUST BE SHOWN TO RECEIVE FULL OR PARTIAL CREDIT Problem 1: Packet switched Network with different link speeds (10 points) Consider a packet-switched, store-and-forward network consisting of three nodes, (two end nodes A and B and one intermediate node with unlimitted buffer capacity), and two transmission links (as shown in figure 1). The first link has bandwidth W 1 bits/sec and propagation delay τ 1 ; the second link has bandwidth W 2 bits/sec and propagation delay τ 2 . Node A has a file of M bits to be transmitted to node B . Each packet has a fixed size header of H bits and a data field of maximum size equal to P bits. Node A starts to send the file at time t = 0. Find the time at which node B recieves the entire file. A B W2, tau2 W1, tau1 Figure 1: Packet Switched Network with different link speeds Problem 2: Circuit Switching vs Packet Switching (14 points) 1

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We are interested in transmitting a fax message of length L bits from a given source location A to a given destination location B. We have two options: the telephone network and a computer network. Telephone Network: C2 = NC1 toll switch A CO C1 tau 0 B CO toll switch C2 = NC1 tau C2 = NC1 tau C1 0 hop 1 hop k Figure 2: Circuit Switching Network. The telephone network is a circuit-switched network. The source and destination nodes are connected to their respective central oﬃces (COs) by twisted pairs of capacity C 1 bits/sec (typically 64 kb/s). The propagation delay on these links is considered to be negligible. The switches in the telephone network (CO switches and toll switches) are interconnected by trunks of capacity C 2 = N C 1 . Each trunk is divided into N separate channels of capacity C 1 ; one of these channels (referred to as the control channel) is dedicated to carrying call setup and acknowledgement messages. We consider that the source and destination COs are separated by K trunks and K 1 toll switches. The propagation delay on the trunks is τ sec.
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