Question

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

Answer 1

Correct Answer - Option 2 : I and III only

Statement I: FALSE:

TCP sequence number of a segment is the byte number of the first byte in the segment. For example, if the segment contains 200 bytes which are from 100 to 199, then the sequence number of the segment would be 100 and the sequence number of the next segment would be 200.

Statement II:TRUE:

To avoid frequent retransmission of a packet, the estimated round trip time at any given point of time is greater than or equal to retransmission time out.

Statement III: FALSE 

Size of the receiver’s buffer never change. Advertised window is the part of the receiver buffer which keeps changing depending upon the processing capability at the receiver's side and the network traffic.

Statement IV: TRUE

The number of unacknowledged bytes at the sender is always less than or equal to the advertised window