EMZETT.Connection
In short: A logical or physical communication channel between two network participants over which data is exchanged.
In more detail: With connection-oriented protocols like TCP, a connection is explicitly established (handshake) and torn down, and its state is maintained for the entire duration of communication. Connectionless protocols like UDP, by contrast, have no persistent connection — each packet is sent independently.
In Depth
A TCP connection goes through a clearly defined lifecycle: establishment via the three-way handshake (SYN, SYN-ACK, ACK), data exchange with ongoing acknowledgement of every packet received, and an orderly teardown via a dedicated FIN/ACK procedure. Throughout the entire connection, both sides hold state information (open sequence numbers, receive buffers, window sizes) — that’s precisely what distinguishes a connection from a single, isolated data exchange.
For connectionless protocols like UDP, by contrast, there’s no explicit setup/teardown and no maintained state: every packet is sent independently, with no guarantee that it arrives, is in order, or even belongs to a “session” at all. This saves overhead, but shifts any needed reliability into the application itself.
In networking, a distinction is often made between the physical connection (the cable/radio link, see line) and the logical connection (the protocol state on a higher OSI layer) — a single physical line can carry many independent logical connections at the same time.
See also: Connectionless Protocol, TCP