ISRO | ISRO CS 2015 | Question 52

An ACK number of 1000 in TCP always means that

(A) 999 bytes have been successfully received
(B) 1000 bytes have been successfully received
(C) 1001 bytes have been successfully received
(D) None of the above

Answer: (D)
Explanation: ACK number in TCP tells which byte it is expecting to receive next.

If Initial sequence number = 1, then ACK number = 1000 would mean 999 bytes delivered.

If Initial sequence number = 0, then ACK number = 1000 would mean 1000 bytes delivered.

Option (C) is never possible because Initial sequence number cannot be -1 (i.e., negative).
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