Connection-Oriented and Connectionless Network Services

Transport protocols are characterized as either connection-oriented or connectionless:

• Connection-oriented services must first establish a connection between the two end-points (sending/receiving) before passing any data traffic between them. An example of a connection-oriented service is Frame Relay, where a VC (virtual connection) is required between both end-points before data traffic can be exchanged. Connection-oriented service involves three phases:

  - Connection establishment

  - Data transfer

  - Connection termination

  During connection establishment, the end-points can reserve resources and negotiate traffic parameters for the connection; for example, to ensure Quality of Service (QoS), further discussed in Chapter 13, “Quality of Service Introduction.”

• Connectionless services can send data without requiring an established connection. Connection-oriented services provide some level of delivery guarantee, whereas connectionless services do not. An example of a connectionless service is any IP service, such as the Internet. No established connection is made between a web browsing user and the home page being viewed.