The main functions of LMI process are:
To determine the operational status of the various PVCs that the router knows about
To transmit keepalive packets to ensure that the PVC stays up and does not shut down due to inactivity
To tell the router what PVCs are available

In addition to the basic Frame Relay protocol functions for transferring data, the Frame Relay specification includes LMI extensions that make supporting large, complex internetworks easier. Some LMI extensions are referred to as common and are expected to be implemented by everyone who adopts the specification. Other LMI functions are referred to as optional.
LMI extensions
Virtual circuit status messages (common)
Multicasting (optional)
Global addressing (optional)
Simple flow control (optional)
In addition to the common LMI features, several optional LMI extensions are extremely useful in an internetworking environment. The first important optional LMI extension is global addressing. With this extension, the values inserted in the DLCI field of a frame are globally significant addresses of individual end-user devices (for example, routers).