6.1 Frame Relay Technology
6.1.1 What is Frame Relay?
Frame Relay is a Consultative Committee for International Telegraph and Telephone (CCITT) and American National Standards Institute (ANSI) standard that defines a process for sending data over a public data network (PDN). It is a high performance, efficient data technology used in networks throughout the world. Frame Relay is a way of sending information over a WAN by dividing data into packets. Each packet travels through a series of switches in a Frame Relay network to reach its destination. It operates at the physical and data link layers of the OSI reference model, but it relies on upper-layer protocols such as TCP for error correction. Frame Relay was originally conceived as a protocol for use over ISDN interfaces. Today, Frame Relay is an industry-standard, switched data link-layer protocol that handles multiple virtual circuits using High-Level Data Link Control (HDLC) encapsulation between connected devices. Frame Relay uses virtual circuits to make connections through a connection-oriented service.

The network providing the Frame Relay interface can be either a carrier-provided public network or a network of privately owned equipment, serving a single enterprise. A Frame Relay network can consist of computers, servers, etc. on the user end; Frame Relay network devices such as switches, routers, CSU/DSUs, or multiplexers.  As you have learned, user devices are often referred to as data terminal equipment (DTE), whereas network equipment that interfaces to DTE is often referred to as data circuit-terminating equipment (DCE), as shown in Figure   .
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