Verilink FrameStart FSD (34-00291.F) Product Manual - Manual (Page 11)

G e n e r a l 5
What is LMI Sourcing and why is it important?
In the most basic implementation, Frame Relay is a simple interface that
offers bandwidth on demand with low latency and high throughput. The UNI
is the user-to-network interface and the LMI (local management interface)
enables both the user and the network to gather information about the UNI.
The LMI allows the user and frame relay network to signal each other about
several activities pertaining to the permanent virtual circuits (DLCIs) on the
link and their physical link status. The LMI provides the following services:
• A polling function to test whether the user or network machine is connected
to the interface
•
A set of operations that inform the user of the addition or deletion of virtual
circuits at the interface
• A report on the status of all virtual circuits on the interface that states whether
or not a virtual circuit is active
• A report on the availability of a new virtual circuit.
LMI information is published in ANSI T1.617, Annex D; ITU-T Q.933,
Annex A; and LMI Revision 1.0.
What is a DLCI?
A DLCI is a data link connection identifier, and is a unique number for each
permanent virtual circuit (PVC) in the frame relay network. The following
DLCI values have been designated for the frame relay network:
0 LMI Channel for ANSI and ITU
1– 15 Reserved
16– 991 For user virtual circuits
992 –1007 Layer 2 management of bearer service
1008 –1022 Reserved
1023 In-channel layer management for LMI Revision 1.0
What messages does LMI provide?
LMI provides for two message types that include a status (S) message and a
status enquiry (SE) message. The SE message is invoked based on a timer
with an upper and lower limit, and the receiving machine responds with a
status message. Depending on the timers and counters used for LMI, the
status element can be either a status request that acts as a link verification
request, or a full status (FS) request that also includes information on all
PVCs on the circuit.
User A User B
Frame Relay
Network
UNI UNI
LMI LMI LMI
UNIT UNIT