3.1 Network Services
3.1.1 Reliable vs. unreliable services
In general, networking protocols and the data traffic they support can be characterized as being either connection-oriented or connectionless. Connection-oriented data handling involves using a specific path that is established for the duration of a connection. Connectionless data handling involves passing data through a permanently established connection. Advantages and disadvantages of each are addressed in the following sections.

A reliable protocol is one that has error correction, flow control, and retransmission capabilities built into it. Unreliable protocols do not have these mechanisms, and they depend on upper-layer protocols to provide reliability. Most connection-oriented protocols are reliable (with some exceptions) and most connectionless protocols are considered to be unreliable.