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End System (ES) is official terminology used in the OSI reference model and by the Internet community to describe a computer or user at the end of a communication link. End systems may be at either end of a straight through point-to-point link or at the edge of a multilink, multihop packet-switched network such as the Internet.

RFC 1136 (Administrative Domains and Routing Domains, A Model for Routing in the Internet, December 1989) describes the terminology of Internet and TCP/IP-routed networks.

David P. Read, one of the people involved in the design of the TCP/IP protocols, discusses the importance of the end-to-end design for the Internet in his paper, "The End of the End-to-End Argument." By splitting the Internet protocols into two protocols (TCP and IP), the network was decentralized and turned into a basic datagram forwarding network. In this model, end systems implemented functions that were previously handled by networks, such as flow control, acknowledgements, and retransmissions. The decentralized model also allowed end-users to deploy applications on their own, so that instead of waiting for some central authority (like the phone company) to decide when a new application could be deployed, end users could run applications on their end systems that used IP's services. This was a radical departure from the network architectures of the time, and it has proved disruptive to the 100-year-old phone system. For example, you can run an Internet phone or videoconferencing application on your computer and communicate with any other Internet user running similar applications. There is no need to involve the telephone company, and the applications can have unique features that are not possible with the telephone system, such as whiteboarding. Read's paper is on the Web at http://www.reed.com/Papers/endofendtoend.html.

The most important feature of transport layer protocols like TCP is their ability to establish an end-to-end (host-to-host) communication session across a connectionless packet-switched network made up of many point-to-pint links. In connection-oriented networks like ATM and frame relay, virtual circuits are established from end to end across a network of switches.

RFC 2775 (Internet Transparency, February 2000) is an interesting read. It describes the current state of the Internet from the architectural viewpoint and concentrates on issues of end-to-end connectivity and transparency.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
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