Nortel DMS-100 Series Maintenance Manual page 47

The DDL facility sets equipped, active channels to available in the
inventory of the DDL facility. A TPT message causes the process to
occur.
The TPT sends a message to the A/B-bit facility. This message requests
the A/B-bit facility to scan equipped, active channels for off-hook.
Call processing sequence of events—originating end
The following sequence of events occurs during call processing at the
originating end of a call:
1 The A/B-bit facility scans for A-bit and B-bit pattern changes, that
indicate if a subscriber goes off-hook. If the A/B-bit facility detects an
off-hook, the A/B-bit facility sends a message to TPT software.
In Mode II, the DDL facility receives a message from the RCS through
the C-field of the DDL message. This message indicates an off-hook
subscriber.
2 In Modes I and III, subscribers a set DS-1 channel assignments.
Assignment of a subscriber line to a channel does not require additional
messaging.
In Mode II, the TPT decodes the message from the A/B-bit facility. The
TPT requests that the DDL facility assign a channel to the subscriber
line. The TPT indicates if a PCM looping test must occur on the DS-1
channel. The DDL facility, through the A/B-DDL message card, sends a
channel assignment message to the RCS.
If the PCM looping test fails, the DDL facility reports the failure to SMS
maintenance. The system disables transmission that uses the DS-1
channel.
3 After the DDL facility assigns a channel, the TPT connects dial tone to
the subscriber loop. The TPT sends dial tone over the DS-1 channel
assigned to the subscriber line.
4 The TPT sends a message to the A/B-bit facility. The TPT requests that
the A/B-bit facility scan for digits.
5 If the subscriber dials digits, the A/B-bit facility digit collection routine
collects the digits. The digit collection routine from the TPT sends the
digits to the TPT. The CM receives the digits from the TPT.
6 The TPT connects audible ringing tone to the subscriber loop. The TPT
sends a message to the A/B-bit facility. The TPT requests that the
A/B-bit facility scan the subscriber loop for on-hook.
DMS-100 Family SMS Maintenance Manual XPM10 and up
Maintenance overview 1-31