Interactive end-of-chapter exercises


Supplement to Computer Networking: A Top Down Approach 8th Edition


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Textbook Cover

End to End Throughput and Bottleneck Links

Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 200 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 60 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 20 Mbps.





You might want to review Figure 1.20 in the text before answering the following questions



Question List


1. What is the maximum achievable end-end throughput (in Mbps) for each of four client-to-server pairs, assuming that the middle link is fairly shared (divides its transmission rate equally)?

2. Which link is the bottleneck link? Format as Rc, Rs, or R

3. Assuming that the servers are sending at the maximum rate possible, what are the link utilizations for the server links (RS)? Answer as a decimal

4. Assuming that the servers are sending at the maximum rate possible, what are the link utilizations for the client links (RC)? Answer as a decimal

5. Assuming that the servers are sending at the maximum rate possible, what is the link utilizations for the shared link (R)? Answer as a decimal




Solution


1. The maximum achievable end-end throughput is the capacity of the link with the minimum capacity, which is 20 Mbps

2. The bottleneck link is the link with the smallest capacity between RS, RC, and R/4. The bottleneck link is Rc.

3. The server's utilization = Rbottleneck / RS = 20 / 60 = 0.33

4. The client's utilization = Rbottleneck / RC = 20 / 20 = 1

5. The shared link's utilization = Rbottleneck / (R / 4) = 20 / (200 / 4) = 0.4



That's incorrect

That's correct

The answer was: 20

Question 1 of 5

The answer was: Rc

Question 2 of 5

The answer was: 0.33

Question 3 of 5

The answer was: 1

Question 4 of 5

The answer was: 0.4

Question 5 of 5

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