Nortel DMS-100 Series Maintenance Manual page 45

The DDL facility maintains an inventory of available DS-1 channels. When
DDL facility receives TPT messages that request channels assignments and
deassignments (Mode II), the DDL facility updates this inventory.
Subscriber lines that connect to a Mode I or Mode III RCS have set DS-1
channel assignments. The state of these channels is open in the inventory.
Software areas, like the A/B-bit facility, use this inventory to find channels
available for work related to these channels.
The A/B-bit facility software module
The A/B-bit facility carries out the following operations associated with A-
and B-bits:
transmission of signaling information to an RCS that requests the
following RCS functions:
— scan subscriber lines
— perform ANI or coin operations
— ring subscriber lines
— stop ringing on subscriber lines
reception of A-bit signaling information from the RCS. The A/B-bit
facility checks the bit patterns for:
— origination
— answer
— flash
— disconnect
— dial pulses for digit collection
— ANI or coin responses
processing of information related to the start or cancellation of the
forward disconnect pattern on a channel
The UP ringing task software module
The UP ringing task and the A/B-bit facility initiate or cancel ringing on a
P-side channel. These components initiate or cancel ringing to respond to a
TPT message.
DMS-100 Family SMS Maintenance Manual XPM10 and up
Maintenance overview 1-29