TCP Socket API: From socket() to accept()

Prerequisites: know that TCP provides a reliable ordered byte stream between endpoints and that a port identifies an application endpoint at a host. Review [TCP flow and congestion control](/notes/computer-networks/tcp-connection-and-congestion-control) if needed.

The socket API is the programming interface used by an application to ask the operating system for network communication. A server's usual passive-open sequence is socket → bind → listen → accept; a client's active-open sequence is socket → connect. After connection setup, both sides use send/recv (or equivalent operations) and close their endpoint when finished.

Each TCP connection is identified by its local and remote IP addresses and port numbers. accept() returns a new connected socket for one client; the original listening socket can continue accepting additional connections. A successful send may transmit fewer bytes than requested, and recv may return a partial application record, so application protocols need framing (for example, a fixed length or explicit length prefix).

UDP is a datagram service and can be contrasted with TCP, but it is not a named transport requirement in the current GATE 2027 CS/IT list. This note introduces only enough UDP semantics to distinguish socket types; it does not present UDP as GATE-core coverage.