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3-6 D-channel handler
format, but only one D-channel (either primary or secondary) can be active
in layer 3 at any one time. The other D-channel is active in layer 2.
Figure 3-2 shows the basic nonassociated signaling of a PRI interface that
contains three DS-1 facilities. It also shows the primary D-channel (D1), and
a secondary D-channel (D2).
Figure 3-2
Nonassociated PRI interface with D-channel backup
MAP commands for D-channel maintenance
PRI D-channel backup extends the existing MAP terminal PRADCH-level
commands to handle the backup D-channel maintenance functions in both
The command function under PRADCH-level handles primary and
secondary D-channel maintenance. The SWACT command supports the
manual switch of activity of D-channels.
D-channel back-up interactions
The following features interact with the D-channel backup:
297-2521-106 Standard 23.01 March 2001
User
Primary D-channel (D1)
Secondary D-channel (D2)
the ISDN central controller
the ISDN multiprocessor system extended peripheral module (XPM)
universal tone receiver on PRI—calls in the digit receiving state are
cleared
basic PRI calls—calls not in the active state are cleared
PRI interface
DS-1
DS-1
DS-1
Network
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