packetlab's video: Frame Relay - Introduction and Concepts - Part 1

Frame Relay - Introduction and Concepts - Part 1 of 4 Frame Relay is a high-performance packet-switched WAN protocol which uses statistical multiplexing and variable length packets. Frame Relay operates at Layer 2 (Data Link) of the OSI model. Each customer gets a private line (or leased line) to a frame-relay node called a virtual circuit (VC) through the Frame Relay cloud. These VCs can either be a bandwidth-on-demand Switched Virtual Circuit (SVC) or (more likely) an always-on Permanent Virtual Circuit (PVC). DTE devices such as a router communicate with a DCE Frame Relay switch. Local Management Interface (LMI) is used to get VC information and as a keepalive between the router and the Frame Relay switch. Each Frame Relay node (DTE) uses a 10-bit data-link connection identifier (DLCI) as a Layer 2 address. These DLCIs are locally significant (although there are extensions that can make them globally significant) and are analogous to MAC addresses in Ethernet. Frame Relay has many powerful features including built-in congestion notification as well as traffic shaping (QoS) capabilities. Although Frame Relay is getting long in the tooth (it's been around since the late 1980s) and technologies like MPLS are quickly rising in popularity, it is still a vary popular WAN protocol and once which you are very likely to work with in the field.