In TCP, a unique sequence number is assigned to each

Key point: TCP assigns a unique sequence number to each byte in the data stream.

Explanation: The sequence number field in the TCP header gives the number of the first data byte carried in that segment (the SYN flag consumes one sequence number). Acknowledgment numbers are cumulative and indicate the next expected byte from the sender.

• Example: If the first byte sent has sequence number 1000 and a segment carries 500 data bytes, the next sequence number will be 1500.

• Purpose: Byte-level numbering enables in-order delivery, loss detection and retransmission, and precise flow control using window fields.

• Why other interpretations are incorrect: Sequence numbers are not assigned to words, entire segments, or high-level messages. Those are units or concepts above the byte stream; TCP's reliability and ACK mechanism operate on byte positions.