What is the process used by TCP to establish a connection?

The process used by TCP to establish a connection is known as the three-way handshake, which involves the exchange of SYN (synchronize) and ACK (acknowledge) messages. This ensures reliable connection establishment between a client and a server.

Here's how the three-way handshake works:

1. SYN message sent by the client: The client sends a SYN packet to the server to initiate a connection. This packet includes a sequence number that the client will use for data transmission.

2. SYN-ACK message from the server: Upon receiving the SYN packet, the server acknowledges the client's request by sending back a SYN-ACK packet. This serves two purposes: it acknowledges the client's SYN message and includes a sequence number from the server as well.

3. ACK message from the client: Finally, the client responds to the server's SYN-ACK with an ACK packet, acknowledging the server’s response. At this point, the connection is established, and data transfer can begin.

This three-step process is vital for ensuring that both parties are ready and synchronized before beginning any data exchange, allowing TCP to provide a reliable, ordered, and error-checked delivery of bytes.

The other options do not align with TCP's connection establishment process.