Best Effort

A "Best Effort" service is one which does not provide full reliability. It usually performs some error control (e.g. discarding all frames which may have been corrupted) and may also provided some (limited) retransmission (e.g. CSMA/CD). The delivered data is not however guaranteed. A best effort service, normally requires reliability to be provided by a higher layer protocol.

Examples of best effort services are:

Link Layer - HDLC (UI frames); Ethernet

Network Layer - IP (Datagrams)

Transport Layer - UDP and UDP-Lite.

Services may be better than best effort, for example provide service guarentees or better expectations of the service. The Differentiated Services (diffserv) and Integrated Services (intserv) frameworks provide this type of service at the network-layer.

There has also been work on less than best effort services, specifically services that are designed to operate in the background. The IP Scavenger service is an example network-layer service that allows file transfers to safely operate in the background without impacting other network users. This service has as yet not been widely used.

See also Reliability.