Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

ES-IS is an OSI (Open Systems Interconnection) protocol that allows communication between end systems (hosts on a network) and intermediate systems (routers that are attached to other networks). The protocol is a discovery protocol similar to the Internet's ARP (Address Resolution Protocol). It allows end systems to take part in internetwork routing.

During the discovery process, the ES and IS find each other. At regular intervals, ESs generate ES Hello messages and send them to every router on the network. Likewise, ISs generate IS Hello messages and send them to every host on their attached subnetworks. The messages transmit OSI network layer and OSI subnetwork addresses. While the process is similar to what happens on IP networks, the terminology is different and beyond the scope of this work, especially in light of the fact that there are very few networks running the OSI protocol suite. Refer to "OSI (Open Systems Interconnection) Model" for more information and Web site references.

At one time, it was thought that OSI protocols would replace the Internet protocols on the government-funded Internet. There are a number of Internet RFCs from the early 1990s that discuss a transition to OSI protocols.

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