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4.51 Confi gure
>
ISDN LAPD
>
LAPD n
Link Access Protocol D (LAPD) is the protocol used for ISDN D-channel signalling and call set up.
Using the Web Page(s)
The
Confi gure
>
ISDN LAPD
folder expands to list separate pages for the LAPD 0, LAPD 1 and
LAPD 2 instances. LAPD2 is normally reserved for ISDN call control. LAPD0 and LAPD1 can be
used as required for SAPI16 traf
fi
c, i.e. D-channel X.25. The con
fi
guration pages allow you to set the
following parameters for each instance.
Enabled:
Setting this parameter to No will disable the LAPD instance. This may be necessary if you have an
installation where two or more units are connected to the same ISDN “S” bus. In this case, only one of
the units may be con
fi
gured for D-channel X.25 on TEI1, SAPI16. On each of the other units you must
disable any LAPD instance for which the TEI is set to 1 in order to prevent it from responding to X.25
traf
fi
c on that TEI that is actually destined for another unit.
DTE/DCE mode:
When the DTE/DCE mode parameter is set to DTE, the unit will behave as a DTE. This is the default
value and should not be changed for normal operation across the ISDN network. If your application
involves using two units back-to-back, one of the units should have the DTE mode value set to DCE.
Keep active:
When this parameter is set to “Yes”, the unit will try to reactivate a D-channel connection after
disconnection by the network by transmitting SABME frames. If it is unable to reactivate the
connection after retrying the number of times speci
fi
ed by the N400 counter, it will wait for 1 minute
before repeating the retry sequence.
If this parameter is set to “No”, the unit will not attempt to reactivate a D-channel link following
deactivation by the network.
Reactivate secs:
This parameter speci
fi
es the number of seconds a deactivation has to be present before the LAPD
instance will try to reactivate itself.
N400 counter:
This is the standard LAPB/LAPD retry counter. The default value is 3 and it should not normally be
necessary to change this.
RR timer (ms):
This is a standard LAPB/LAPD “Receiver Ready” timer. The default value is 10,000ms (10 seconds)
and it should not normally be necessary to change this.
Deactivation:
This parameter can be set to “Active” or “Passive”. When set to “Passive”, the unit will not deactivate
a LAPD session when an X.25 PAD session is terminated using the log command. To enable
automatic deactivation of a LAPD session the option should be set to “Active”.
T1 timer (ms):
This is the standard LAPB/LAPD timer. The default value is 1000 milliseconds (1 second) and it
should not normally be necessary to change this.
T200 timer (ms):
This is the standard LAPB/LAPD re-transmit timer in milliseconds. The default value is 1000
milliseconds (1 second) and it should not normally be necessary to change this.
