Reliability (computer networking)

This definition was formerly listed for connection-oriented, but was refactored due to inaccuracies.

In computer networking, a reliable protocol is one that ensures data arrival via some internal method, as opposed to an unreliable protocol, which does not guarantee than all the data will arrive (or indeed, at all).

Reliable protocols are slightly slower and have more overhead than an unreliable protocol, but often this isn't an issue. TCP, the main protocol used in the Internet today, is a reliable protocol. UDP, often used in computer games or other situations where speed is an issue and the loss of a little data is not, is unreliable.

Most often, a reliable protocol is also connection-oriented. However, this is not always so. For example, TCP is a connection-oriented protocol, with the virtual circuit ID consisting of source and destination IP addresses and port numbers. However, there are also unreliable protocols that are connection-oriented as well. Among these include ATM and Frame Relay, on which 90% or more of all Internet traffic is passed.