Suppose the route between your host and a server has a fixed RTT of 110ms. The b

Question

Suppose the route between your host and a server has a fixed RTT of 110ms. The bottleneck link is 8Mbps. Ignore queueing delay and assume that the bottleneck simply drops once a sender's window is larger than 110,000 bytes. You may assume packets are only lost to drops on the bottleneck link. The TCP initial congestion window is 10kB (10,240 bytes). The server can process requests instantly. You are using TCP Reno. Assume this setup in all questions in this quiz.

1. Using HTTP 1.0, you request a 20kB file. How long will it take to download the last byte of the file in ms?

2. Approximately what percentage (integer 0 to 100) of the bottleneck link capacity does this use?

Explanation / Answer

1. Since the file size is 20kB, we will send with (1, 2, 4, 8, 16) totalling 31kB of data. This would take 5 RTTs. There would be another RTT for opening the TCP connection. This gives us 6 RTTs for the file to be transferred. Since one RTT is 110ms, it would take 660ms to download the last byte of the file.

2. Percentage Bottleneck Link Capacity : 100kB / 0.55s = 186kBps = 18.6%

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