Frame Relay

Frame Relay:
Frame Relay has the following characteristics:
• successor to X.25
• has less overhead than X.25 because it relies on upper layer protocols to perform error checking.
• Speed in between the range of 56 Kbps to 2.078 Mbps.
• uses Data Link Connection Identifiers(DLCI) to identify virtual circuits, with DLCI number between 16 and 1007.
• uses Local Management Interfaces(LMI) to provide info on the DLCI values as well as the status of virtual circuits. Cisco routers support Cisco(Default), ANSI and Q933a.
• to set up frame relay, we need to set the encapsulation to frame-relay in either the Cisco(Default) mode or the IETF mode, although Cisco encapsulation is required to connect two Cisco devices.
• LMI type is configurable, but by default it is being auto-sensed.
• generally transfer data with permanent virtual circuits (PVCs), although we can use switched virtual circuits (SVCs) as well.
• SVC is for transferring data intermittently.
• PVC does not have overhead of establishing and terminating a circuit each time communication is needed.
• Committed Information Rate(CIR) is the guaranteed minimum transfer rate of a connection

Cisco has a web page that describes the configuration and troubleshooting of Frame relay at http://www.cisco.com/warp/public/125/13.html