# GATE Papers >> CSE >> 2015 >> Question No 23

Question No. 23

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?

 I. If the sequence number of a segment is m, then the sequence number of the subsequent segment is always m+1. II. 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. III. The size of the advertised window never changes during the curse of the TCP connection. IV. The number of unacknowledged bytes at the sender is always less than or equal to the advertised window.

##### Answer : (B) I and III only

Solution of Question No 23 of GATE 2015 CSE Paper

Statement 1 is false because, the sequence number of the subsequent segment depends on the number of byte characters in the current segment.

Statement 2 True, because RTO timer is always $\geq$ Estimated RTT.

Statement 3 False. Receiver window is used to give the sender an idea of how much free buffer space is available at the receiver.

Statement 4 is true, TCP is not permitted to overflow the allocated receiver buffer.

Hence when the sender cannot send any more data receiver window would be 0 and hence. The buffer would have unacknowledged data.

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