1. Computer Network
Assignment 2
Submission Deadline : Sunday, Nov 13 Mid Night
Q1. Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then Timeout for the
connection will necessarily be set to a value >= 1 sec.
Q2. Write down the equation to calculate EstimateRTT?
Q3. For congestion control in TCP, if a timer expires, would timer value be set to one half of its
previous value? (We didn't discuss this in the class. I want you to find out the answer of this
quesiton. For reference, refer to the following book written by Douglas E. Comer, Internetworking
with TCP/IP Vol.1 4th edition, page no. 226, topic name is Timeout and Retransmission. I know
there have few copies of this book in the library)
Q4. Recall the lecture on Sequence Number in TCP Protocol? Is it represent the byte-numbered
position relative to the start of the file or the first byte of segment?
Q5. How does TCP Reno respond for a loss event detected by triple duplicate ACK
(a) cuts its congestion window to 1 Maximum Segment Size (MSS).
(b) goes to fast recovery phase.
(c) goes to slow-start phase.
(d) Both (a) and (c).
Q6. To calculate the timeout interval in TCP, which parameter(s) is/are used?
(a) Sample Round Trip Time (RTT).
(b) RTT Estimate.
(c) Average congestion window size.
(d) Both (a) and (b).
Q7. Host A wants to send a file to host B as fast as possible (as less delay as possible). Which
transport protocol is recommended?
(a) TCP.
(b) UDP.
(c) FTP.
(d) HTTP.
Q8. Which of the following is true for FTP in-context of Transport Layer.
(a) FTP usually uses more bandwidth than HTTP or SMTP.
(b) FTP uses two UDP connections simultaneously.
(c) FTP uses two TCP connections simultaneously.
(d) Both (a) and (b).
(e) Both (a) and (c).
Q9. What information, from the following, does a process running on Host A need to identify
another process running on Host B.
(a) The data rate between Host A and Host B in bits/sec.
(b) IP address of Host B.
(c) Port number of Host B.
(d) Both (b) and (c).
(e) All of the above.
Q10. Why is circuit-switched network superior to packet-switched network?
(a) It can support wireless connections.
(b) It can be implemented over fiber-optic link.
(c) It can provide the same services with less overhead.
(d) It can guarantee a certain amount of end-to-end bandwidth.
(e) All of the above.

2. Q11. Among the following, what does TCP doesnt need to keep track of?
(a) Local port.
(b) Number of open connections.
(c) Sequence numbers.
(d) Congestion window size.
Q12. Consider 2 hosts A and B sepearted by l routers, Each router has transmission rate of
R bps, refer figure below
(Fig : Note that there are l (not one, but letter L) routers.).
We assume that the links are not congested and hence there are no queuing delays.
Host A has a file of size P bits to send. Host A divides the file into n segments, each segment of size
M bits, such that P = n * M. Host A then adds X bits, as header, to each segment and makes a packet
of size M+X bits.
For what value of M, is the delay of sending the file from A to B is minimum.
(Hint: You would require to use differentiation to calculate the minimum – recall differentiation
from calculus. Also recall how do you find minimum and maximum.)
Q12. Input the sequence numbner, acknowledgment number, and segment length entries in Table 1
for the following TCP connection illustration.
You can make the following assumptions:
1.Receiver never timeouts.
2.Sender starts transmission at time t1.
3.Data flows in both direction i.e. The connection is full duplex.
4.Acknowledgemnts are not delayed.
Q13. What would be the timout value, in Fig above, for the segment with the sequence number 140.