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Suppose two hosts use a TCP connection to transfer a large file. Which of the following statements is/are FALSE with respect to the TCP connection?

  1. If the sequence number of a segment is $m,$ then the sequence number of the subsequent segment is always $m+1.$
  2. If the estimated round trip time at any given point of time is $t$ sec, the value of the retransmission timeout is always set to greater than or equal to $t$ sec.
  3. The size of the advertised window never changes during the course of the TCP connection.
  4. The number of unacknowledged bytes at the sender is always less than or equal to the advertised window.
  1. III only
  2. I and III only
  3. I and IV only
  4. II and IV only
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35 votes

Option B

III. False. It is the size of the receiver's buffer that's never changed. RcvWindow is the part of the receiver's buffer that's changing all the time depending on the processing capability at the receiver's side and the network traffic.

http://web.eecs.utk.edu/~qi/teaching/ece453f06/hw/hw7_sol.htm

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This problem is taken from tanenbaum exercise .

I is directly taken , see 2 d) here http://web.eecs.utk.edu/~qi/teaching/ece453f06/hw/hw7_sol.htm

II is also in above link but indirectly , see  2 f) 

III  it is also direct from tanenbaum, see above link 2 b) 

IV Indirectly taken , see question number  2 c) 

13 votes
13 votes
1.False : because in tcp every byte is numbred and header contains the sequence number of 1st byte so sequence number in 2nd packet will be the next sequence number of last bit in 1st packet.

2. true:consider either the basic algorithm or jacobsn algorithm the value of timeout is always set > rtt for next transmission.

3.false: adv value in tcp header is dynamically changed by receiver each time.

4.true: window size at the receiver is always less than or equal to re1ceiver window size and thus the number of unacknowleged bytes can never exceed advertized window at that time.
11 votes
11 votes

Option B.
Reason for I to be wrong: The sequence number of the subsequent segment depends on the number of 8-byte characters in the current segment. Transfer in TCP is byte ordered.

Answer:

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