Question

Given below are two statements :
one is labelled as
Assertion (A) and the other is labelled as
Reason (R).
Assertion (A) :
TCP uses sequence numbers to ensure reliable, in-order delivery of data segment.
Reason (R) :
Sequence number helps detect packet duplication and reordering in transmission.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Think of sequence numbers like page numbers in a book. If you drop the book and the pages scatter, you can only put them back in order because the numbers tell you exactly where each page belongs!

Answer 1

The Correct Option is A

Transmission Control Protocol (TCP) is a connection-oriented protocol that provides reliable delivery. 1. Evaluating Assertion (A): One of the core features of TCP is its ability to take a stream of data, break it into segments, and ensure they are reconstructed perfectly at the destination. The sequence number field in the TCP header tracks the byte stream position. This allows the receiver to put the segments back in the correct order. Thus, Assertion (A) is correct. 2. Evaluating Reason (R): IP packets (which carry TCP segments) can take different paths through the internet, leading to them arriving out of order or being duplicated by routers.
• Reordering: The receiver uses the sequence numbers as an index to sort incoming packets.
• Duplication: If a receiver gets two packets with the same sequence number, it knows the second one is a duplicate and discards it. Thus, Reason (R) is correct. 3. Final Linkage: Because sequence numbers provide the mechanism to solve reordering and duplication, they are the reason why TCP is able to provide reliable, in-order delivery. Therefore, (R) is the correct explanation of (A).