User`s guide

XSR User’s Guide 127
Chapter 7 Link Management Information (LMI)
Configuring Frame Relay
Link Management Information (LMI)
A Frame Relay switch communicates with another Frame Relay switch or an
attached Frame Relay DTE device (e.g., the XSR) about the status of the PVC
connections through Link Management Information protocol (LMI).
LMI monitors the status of the connection and provides the following data:
 Active/inactive interface - known as a keep alive or heartbeat signal.
 The valid DLCIs defined for that interface.
 The status of each DLCI (either New, Activate or Delete).
Three versions of the LMI specification as described below:
Protocol
Specification
ILMI, (OGOF) Frame Relay Forum Implementation Agreement (IA)
FRF.1 superseded by FRF.1.1
Annex D (ANSI) ANSI T1.617
Annex A (Q933a) ITU Q.933
The protocol defined for the LMI provides a status inquiry message which the
the XSR can send, either as a keep alive message to inform the network that the
connection to the router is still up, or as a request for a report on the status of
the PVCs on that port. The network then responds with a status message,
either in the form of a keep alive response or full report on the PVCs.
An optional status update message lets the network unilaterally report a PVC
status change. An LMI status query provides for one-way querying and one-
way response only, meaning that only the XSR can send a status inquiry
message, and only the network can respond with a status message. Using
status inquiries in this manner renders both sides of the interface unable to
provide the same commands and responses.
In contrast to the ILMI (which uses DLCI 1023), Annex D reserves DLCI 0 for
PVC status signaling. The current requirement in Annex A signaling is similar
to Annex D and also uses DLCI 0.