Link Management protocols are used by a node in a nework to monitor individual connections ie. Private Virtual Circuits (PVC's). Other changes are also communicated using LMI.
The end device in a network (DTE) sends Status Enquiry message to the network node every polling interval (heartbeat). The node responds with a status message that verifies the link integrity.
After a set number of these exchanges (usually 6), the DTE equipment requests a full update. This includes the status of all PVC's (new, deleted and exisiting) terminating at the DTE.
With the Annex protocols (discussed below) the full updates occur randomly. There are three main parameters for this operation: a) heartbeat, b) timeout and c) status rate.
There are three main types of LMI:
- LMI Protocol
- Annex D Protocol
- Annex A Protocol
LMI Protocol
Also known as Strata LMI - developed by the "Group of Four".
LMI protocol will support both LMI user interface termination and LMI network where the interface terminates on an end user device.
The LMI protocol is essential in that it will provide a heartbeat signal to ensure PVC is functional, it informs end user devices of new and deleted PVC's and it tells the nodes of the status of each PVC (end to end) ie. circuit is up or down.
Strata LMI uses DLCI 1023
Annex D Protocol
This protocol is the result of ANSI (American National Standards Institute) work. As usual, in this industry, all the players couldn't get their act together to come up with one standard.
There are three Annex protocol types: user, network and bi-directional.
Annex A Protocol
This protocol comes to us from CCITT's link management specs.
Like Annex D, it uses DLCI 0. It also has the same three protocol types.
Back
Forward
