Local management interface type (LMI) for Frame Relay

The LMI (Local management interface, locally Management Interface) is the signaling standard between the CPE device (router) and the frame switch, adding extensions to the Frame Relay protocol for managing complex interconnection networks. The main Frame Relay LMI extension includes global addressing, virtual circuit state messages, and multicast.
Note: There are in fact 3 LMI criteria. In addition to the Cisco LMI (developed in 1990 by Cisco System, StrataCom, Northern Telecom and Digital Equipment Corporation), there are ANSI and Q.933A standards.
The LMI global addressing extension makes the Frame relay DLCI value Global rather than local significance. The DLCI value becomes the only DTE address in the Frame Relay WAN. Global addressing extensions add the functionality and manageability of the Frame Relay interconnect network. For example, you can use standard address resolution and discovery techniques to identify each network interface and end node that is connected to an interconnected network.
In addition, the entire Frame relay network (for routers) looks like a typical LAN.
The LMI virtual Circuit status message provides communication and synchronization between the frame relay DTE and DCE devices. These messages are used to periodically report the state of the PVC, preventing data from being sent into the black hole (i.e. no longer exists on the PVC).
An LMI multicast extension allows multicast groups to be allocated. Broadcast technology allows routing updates and address resolution messages to be sent only to specific router groups, and multicast saves bandwidth. The extension also transmits reports about the status of multicast groups in the update message.
Cisco LMI, ANSI, and q.933a have multiple versions. Cisco LMI, ANSI, and q.933a all provide information about the ISDN configuration and the status of the virtual circuit. The LMI type configured on the router must match the LMI type used by the service provider. In addition, the LMI types must be the same at both ends of the connection.