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248 CHAPTER 17: CONFIGURING FRAME RELAY
When the Frame Relay interface type is DCE or NNI, the default type of LMI
protocol of interface is Q933a. When the Frame Relay interface type is DTE, the
default LMI protocol of interface is null.
4 Configure the Related Parameters of Frame Relay LMI Protocol
The procedure of the LMI protocol is as follow:
■ DTE sends out a status enquiry message, and the timer T391 starts. T391 is set
with the polling interval. In other words, DTE will send a status enquiry
message at each interval of T391. Simultaneously, the counter V391 at the DTE
side will start. If V391 < N391, The status enquiry message sent by DTE will
only inquire the “link integrity”. If V391 = N391, it will clear all. In this case,
besides inquiring the “link integrity”, the status enquiry sent by DTE will inquire
the statuses of all the PVCs, which is called “Full Status Message Polling”.
■ Upon receiving the enquiry message, DCE respond to the status enquiry
message by sending the status message. Simultaneously, the polling
authentication timer T392 at the DCE side starts, and DCE waits for the next
status enquiry message. Upon the timeout of T392, if DCE receives no status
enquiry messages, it will record this error and add 1 to the number of errors.
■ Upon receiving the status response message, DTE knows the link status and
PVC status. When DCE responds to the status enquiry message, it should
respond the status message of all the PVCs if the PVC status on the network
changes or there is PVC added or deleted, irrespective of DTE inquires for the
PVC status or not,. Thereby, DTE can know the changes on DCE side, and
update the record based on that information.
■ If the timer T391 times out, but no status message is received yet at the DTE
side to respond to that, this event error will be recorded and 1 will be added to
the number of errors.
■ If the number of errors in N393 events exceeds N392, DTE or DCE will assume
that the path is usable but all the virtual circuits are unusable. N393 represents
the total number of observed events, and N392 represents the error threshold.
You can configure the various counters and thresholds of the frame relay LMI
protocol, to optimize the running efficiency of equipment at the DTE and DCE
sides.
Perform the following configurations in synchronous interface view.
Table 277 Configure the related parameters of Frame Relay LMI protocol
Operation Command
Set the counter on PVC status enquiry messages
(N391 DTE)
fr lmi n391dte [ n391-value ]
Restore the default value of the counter on the
PVC status enquiry messages
undo fr lmi-n391dte
Set the LMI error threshold (N392 DCE) fr lmi n392dce [ n392-value ]
Restore the default value of the LMI error
threshold
undo fr lmi n392dce
Set the LMI error threshold (N392 DTE) fr lmi n392dte [ n392-value ]
Restore the default value of the LMI error
threshold
undo fr lmi n392dte
Set the LMI event counter (N393 DTE) fr lmi n393dte [ n393-value ]
Restore the default value of the LMI event
counter
undo fr lmi n393dte
Set the LMI event counter (N393 DCE) fr lmi n393dce [ n393-value ]