Nortel NT1R20 Description page 69

During outgoing calls from the terminal equipment, a
Outgoing Calls
channel is seized when the terminal equipment goes off-hook, simulating a
ground to the ring lead toward the line-side T1 card by causing the line-side
T1's receive B bit to change from 1 to 0. In turn, the line-side T1 card
simulates grounding its tip lead by changing the transmit A bit to 0. The
terminal equipment responds to this message by removing the ring ground
(line-side T1's receive B bit is changed to 1) and simulating open loop at the
terminal equipment (line-side T1's receive A bit is changed to 0).
Call disconnect from far end (PSTN, private network or local station
While a call is in process, the far end may disconnect the call. If the line-side
T1 port has been configured with the supervised analog line (SAL) feature,
the line-side T1 will respond to the distant end disconnect message by
opening tip ground. This causes the line-side T1 card to change the transmit
A bit to 1. When the terminal equipment sees the transmit A bit go to 1, it
responds by simulating open loop causing the line-side T1's receive A bit to
change to 0. The call is terminated and the interface is once again in the idle
condition.
For the line-side T1 card to support distant end disconnect in ground start
mode, the following configuration parameters must exist:
— X11 software release 21 or later is required and the Supervised Analog
Line (SAL) feature must be configured for each line-side T1 port.
Note: By default, the SAL feature opens the tip side for 750 m/s in loop
start operation. This is configurable in 10 m/s increments.
— In order to detect distant end disconnect for calls originating on the
line-side T1 card, the "battery reversal" feature within the SAL software
must be enabled. Enabling the "battery reversal" feature will not provide
battery reversal indication when a call is answered; it will only provide
battery reversal indication when a call is disconnected.
— In order to detect distant end disconnect for calls terminating on the
line-side T1 card, the "hook flash" feature within the SAL software must
be enabled.
— In order to detect distant end disconnect for calls originating and
terminating on the line-side T1 card, both the "battery reversal" and
"hook flash" features within the SAL software must be enabled.
Description Page 45 of 290
Line cards Description