What is the purpose of the Initial Sequence Number (ISN) in TCP?

The Initial Sequence Number (ISN) in TCP plays a crucial role in ensuring the reliability and order of data transmission across networks. Its primary purpose is to randomize the starting sequence number used for a TCP connection, which helps in preventing certain types of attacks, such as session hijacking. By utilizing a random ISN, TCP provides a level of security that makes it difficult for potential attackers to predict the sequence number, thus enhancing the integrity and confidentiality of the connection.

Using a random ISN also allows for multiple simultaneous connections to be established between the same devices without confusion, as each connection can be uniquely identified by its starting sequence number. This randomization is vital in ensuring that data packets are tracked correctly and can be reassembled in the right order once received.

In contrast, identifying connection ports pertains to how devices communicate over the network and does not relate directly to sequence numbering. Establishing a secure connection generally involves encryption protocols and techniques beyond just the sequence numbers used in TCP. Lastly, confirming receipt of data is managed through acknowledgments in TCP, not through sequence numbering directly, although sequence numbers do play a role in the overall process by keeping track of data integrity and order during transmission.