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The NFAS option provides D-channel redundancy when both the in service (IS) D-channel fails and a backup D-channel is defined for the NFAS group. This appendix provides graphic representations of the state transitions occurring on the primary D-channel and backup D-channel during channel initialization and switchover. Channel states are displayed on the NFAS Group Configuration screen described in "Non-Facility Associated Signaling (NFAS)." The figures in this appendix do not provide a complete description of D-channel backup processing. Only the typical states that appear on the NFAS Group Configuration screen are represented.
Figure C-1 represents D-channel initialization as the system attempts to establish a link with the far-end connected equipment. During initialization, the system always attempts to bring the primary D-channel (D1) into the in service (IS) state before attempting to make the backup the controlling D-channel. The solid lines in Figure C-1 indicate this preferred initialization path.
Figure C-2 demonstrates the state transitions during automatic and manual D-channel switchovers.
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Note Figure C-2 assumes that the primary D-channel (D1) is currently in service (IS) while the backup D-channel (D2) is in standby (STBY) state. Switchover processing between the IS channel and the STBY channel is the same regardless of which channel (primary or backup) is currently in IS state. |
In both figures, channels that are in IS state (supporting stable calls and allowing new call attempts) are shown in white. Channels that are unable to support new call attempts (in STBY, WAIT, MB, or OOS state) are shaded.
Posted: Fri Jan 23 12:19:49 PST 2004
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