Education Assignment 2CR

1, True or false? Please explain your answers. (10 points) a, Host A is sending Host B a large file over a TCP connection. Assume Host B has no data to send Host A. Host B will not send acknowledgements to Host A because Host B cannot piggyback the acknowledgements on data.

b, The size of the TCP RcvWindow never changes throughout the duration of the connection.

c, Suppose Host A is sending Host B a large file over a TCP connection. The number of unacknowledged bytes that A sends to B cannot exceed the size of the receive buffer in Host B.

d, Suppose Host A is sending a large file to Host B over a TCP connection. If the sequence number for a segment of this connection is m, then the sequence number for the subsequent segment must be m+1.

e, The TCP segment has a field in its header for RcvWindow.

2, (6 points) Suppose Host A sends two TCP segments back to back to Host B over a TCP connection. The first segment has sequence number 400 and the second has sequence number 1000. a, How much data is in the first segment? b, Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgement that Host B sends back to Host A, what will be the acknowledgement number?

3, (8 points) UDP and TCP use 1s complement for their checksums. Suppose you have the following three 8-bit bytes: 01011111, 01110000, 11001001. What is the 1s complement of the sum of these 8-bit bytes? (Note that although UDP and TCP use 16bit words in computing the checksum, for this problem you are being asked to consider 8bit sums.) Show all work. Why is it that UDP takes the 1s complement of the sum; that is. Why not just use the sum? With the 1s complement schema, how does the receiver detect errors? Is it possible that a 1-bit error will go undetected? How about 2-bit error?

4, (12 points) Consider the following plot of TCP window size as a function of time. Assume TCP Reno is the protocol experiencing the behavior shown above, answer the following questions. In all cases, you should provide a short discussion justifying your answer.

a, Is TCP Congestion avoidance operating in interval [6, 16]? Why or why not? b, Is TCP congestion avoidance operating in interval [23, 26]? Why or why not? c, After the 16th transmission round, is segment loss detected by a triple duplicate ACK or by a timeout? Why?

d, After the 22nd transmission round, is segment loss detected by a triple duplicate ACK or by a timeout? Why? e, What is the value of Threshold at the 25th transmission round? f, What is the value of Threshold at the 20th transmission round?

5, What is the difference between routing and forwarding? (4 points)

6, What is the role of the forwarding table within a router? What is meant by destinationbased forwarding? How does this differ from generalized forwarding? (4 points)

7, What is HOL blocking? Does it occur in input ports or output ports? (4 points)

8, Do routers have IP addresses? If so, how many? How many IP addresses does a computer have? (4 points)

9, Is it necessary that every autonomous system use the same Intra-AS routing algorithm? Why or why not? Name two intra-AS routing algorithms. (4 points)

10, Consider the following network topology:

Assume the original routing table in D is as below.

Now suppose that D receives from A the following advertisement:

Will the table in D change? If so how? (4 points)