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2013_Midterm_1_Exam_Solution

# Answer server can send at the max of the bottleneck

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Unformatted text preview: , each client is connected by a separate pair of wires to the DSLAM. Problem 2: Delays, Throughput and Caches (24 Points, 20 minutes) Consider the scenario shown in Figure 1 in which a server is connected to a router by a 100Mbps link with a 50ms propagation delay. Initially this router is also connected to two routers, each over a 50Mbps link with a 200ms propagation delay. A 1Gbps link connects a host and a cache (if present) to each of these routers and we assume that this link has 0 propagation delay. All packets in the network are 20,000 bits long. Server 100 Mbps 50 ms 50 Mbps 200 ms 50 Mbps 200 ms 1 Gbps 0 ms 1 Gbps 0 ms Client Cache Client Figure 1 Cache a. (4 Points) What is the end- to- end delay from when a packet is transmitted by the server to when it is received by the client? In this case, we assume there are no caches, there’s no queuing delay at the routers, and the packet processing delays at routers and nodes are all 0. Answer: If all packets are 20,000 bits long it takes 200 usec to send the packet over the 100Mbps link, 400 usec to send over the 50Mbps link, and 20 usec to send over the 1Gbps link. Sum of the three- link transmission is 620 usec. Thus, the total end- to- end delay is 250.62 msec. ECE374: First Midterm 4 b. (4 Points) Here we assume that client hosts send requests for files directly to the server (caches are not used or off in this case). What is the maximum rate at which the server can deliver...
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