Enterasys Networks Security Router X-PeditionTM - Manual (Page 215)

Link Management Information (LMI)
XSR User’s Guide 9-7
Link Management Information (LMI)
A FR UNI-DCE device communicates with an attached FR 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 are listed in Table 9-1 below:
The protocol defined for the LMI provides a status enquiry message which 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. A 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. ILMI and AUTO mode can support only 190 DLCIs per interface due to Status message size
limitations. Annex D and A can support up to 300 DLCIs per interface.
Each version includes a slightly different use of the management protocol. The XSR implements
UNI-DTE and UNI-DCE for all three LMI types as well as auto, which is the default option for the
frame-relay lmi-type command. Auto is the fastest LMI type to discover and activate DLCIs.
Sub-interfaces
The XSR implements FR as a multi-access media in which one interface to the network - the
physical link - has one or more destinations, namely, virtual connections which are grouped with
their corresponding physical link. For this purpose, the XSR groups one or more PVCs under
separate sub-interfaces, which in turn are associated with a single physical interface.
FR sub-interfaces are created with the interface serial <multi-point | point-to-point>
command. The frame-relay interface-dlci command assigns a DLCI to a sub- interface and
the class command assigns a map class to a DLCI on a sub-interface.
Table 9-1 LMI Specifications
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
Note: Be sure the same version of the management protocol resides at each end of the FR link
except for Auto.