Frame Relay is a connection-oriented data-link technology that defines single-link virtual circuit multiplexing by assigning connection identifiers.
Cisco routers support the following five Frame Relay serial connections:
- EIA/TIA-232
- EIA/TIA-449
- V.35
- X.21
- EIA/TIA-530
Frame Relay has numerous operation compontents and terms associated with it, such as local access rate, virtual circuit, PVC, SVC, Data-Link connection identifier, CIR, Inverse ARP, LMI, FECN, and BECN.
In a Frame Relay virtual circuit connection, the local DLCI destination Network Layer address can be mapped dynamically with Inverse ARP or manually, by configuring a static Frame Relay map in the map table.
Local Management Interface (LMI) is a signaling standard between the router and the Frame Relay switch that is responsible for managing the connection and maintaining status between the devices, and is available in three central types for Cisco routers: cisco, ansi, and q933a.
The Local Management Interface (LMI) signaling works in the following process:
- Router connects to Frame Relay switch.
- Router sends message to Frame Relay switch.
- Frame Relay switch receives the request and responds.
- Router sends Inverse ARP packet introducing itself.
- Router creates map entry in Frame Relay table or table is configured.
- Router exchanges LMI information with switch.
Frame Relay is configured on a router using the encapsulation frame-relay, frame-relay lmi-type, and frame-relay inverse-arp commands.
The IOS command sequence encapsulates Frame Relay, sets the LMI connection, and enables Inverse ARP on a router.
Frame Relay configuration and implementation information can be displayed using the various show frame-relay and the debug frame-relay commands.
Static maps that define the address-to-DLCI table statically are configured using the frame-relay map command.
The three WAN topologies used to interconnect remote sites are star, partial mesh, and full mesh.