Consider the three way hand shaking process followed during TCP connection establishment between two hosts A and B . Let S and R be two random 32 -bit starting sequence numbers chosen by A and B, respectively. Suppose A sends a TCP segment having SYN bit =1, SEQ number = S and ACK bit =0 and B accepts the connection request. Which one of the following choices represents the information present in the TCP segment header that is sent by B to A ?

1. ASYN bit =1, SEQ number =S+1, ACK bit =0, ACK number =R, FiN bit =0
2. BSYN bit =0, SEQ number =R, ACK bit =1, ACK number =S+1, FiN bit =0
3. CSYN bit =1, SEQ number =R, ACK bit =1, ACK number =S+1, FiN bit =0
4. DSYN bit =1, SEQ number = R, ACK bit =1, ACK number =S, FiN bit =0

Pick an option to check yourself, or open the answer below.

Show answer & explanation

Correct answer: C. SYN bit =1, SEQ number =R, ACK bit =1, ACK number =S+1, FiN bit =0

Explanation

B replies with SYN-ACK: SYN = 1, its own initial sequence number R, ACK = 1, and acknowledgement number S + 1 (the SYN consumes one sequence number).