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(COMP361)Midterm2_Fall02.pdf
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COMP 361 Computer Communications Networks
Fall Semester 2002
Midterm Examination 2
Date: November 14, Time 16:30pm : 17:50pm



Instructions:
1. This is a closed book exam

2. This examination paper consists of 5 pages and 7 questions

3. Please write your name, student ID and Email on this page.

4. For each subsequent page, please write your student ID at the top of the page in the space provided.

5. Please answer all the questions within the space provided on the examination paper. You may use the back of the pages for your rough work.

6. Please read each question very carefully and answer the question clearly and to the point. Make sure that your answers are neatly written, readable and legible.

7. Show all the steps you use in deriving your answer, where ever appropriate.

8. For each of the questions assume that the concepts are known to the graders. Concentrate on answering to the point what is asked. Do not define or describe the concepts.



Question
Points
Score

1
10


2
15


3
10


4
10


5
20


6
15


7
20



TOTAL
100







1. Answer the following true/false questions by circling either T or F (10 points)

(a) Host A is sending host B a large file over a TCP connection. Assume host B has no data to send to A. Host B will not send acknowledgements to host A because host B cannot piggyback the acknowledgements on data.

(b) The size of 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 cannot exceed the size of the receive buffer.

(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 will necessarily be m+1.

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

(f) Suppose that the last SampleRTT in a TCP connection is equal to 1sec. Then Timeout for the connection will necessarily be set to a value >= 1 sec.

(g) Suppose host A sends host B one segment with sequence number 38 and 4 bytes of data. Then in this same segment the acknowledgement number is necessarily 42.

(h) Consider congestion control in TCP. When a timer expires at the sender, the threshold is set to one half of its previous value.

(i) Every autonomous system uses the same intra-autonomous system routing algorithm.

(j) Hierarchical organization of the Internet has helped to scale to millions of users.

2. Consider a general topology and a synchronous version of distance vector algorithm (in one iterative step all the nodes compute their distance tables at the same time and then exchange them ). Suppose that