Question

Assume Alice, the client, creates a TCP connection with Bob, the server. They exchange data and close the connection. Now Alice starts a new connection with Bob by sending a new SYN segment. The server responds with the SYN + ACK segment. However, before Bob receives the ACK for this connection from Alice, a duplicate old ACK segment from Alice arrives at Bob's site. Can this old ACK be confused with the ACK segment Bob is expecting from Alice?

Answer 1

TCP connections are uniquely identified by a four-tuple and a sequence number, ensuring that old ACK segments from a previous TCP connection cannot be confused with ACKs from a current connection due to the synchronization of sequence numbers during the TCP handshake process.

Step-by-step explanation:

The question concerns the Transmission Control Protocol (TCP), specifically regarding the handling of duplicate ACK segments in a new connection establishment process. In TCP, each connection is uniquely identified by a four-tuple: source IP address, source port, destination IP address, and destination port, combined with a sequence number that distinguishes new segments from old ones.When Alice initiates a new connection, a new initial sequence number is generated which prevents the old ACK from being confused with the new ACK that Bob is expecting. This mechanism is integral to TCP's reliability, ensuring that segments from old connections do not interfere with current connections. Additionally, TCP includes a handshake process with SYN, SYN+ACK, and ACK segments that serve to synchronize the sequence numbers between client and server, which further helps to distinguish between new and old segments.Therefore, the old ACK segment from a previous connection will not match the current sequence numbers and should be ignored by the server, ensuring that it cannot be mistaken for an ACK in the current connection establishment process.