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NT8D14 Universal Trunk card Page 561 of 894
Circuit Card Description and Installation
provides the means for analog loop terminations to establish, supervise, and
take down call connections.
Signaling interface
All trunk signaling messages are three bytes long. The messages are
transmitted in channel zero of the DS-30X in A10 format.
Configuration information for the Universal Trunk card is downloaded from
the CPU at power-up or by command from maintenance programs. Eleven
configuration messages are sent. Three messages are sent to the card to
configure the make/break ratio and A-Law or µ-Law operation. One message
is sent to each unit to configure the trunk characteristics.
Operation
Administrators can assign optional applications, features, and signaling
arrangements for each unit on the NT8D14 Universal Trunk card through the
Trunk Administration LD 14 and Trunk Route Administration LD 16
programs or jumper strap settings on the card.
Loop start operation
Loop start operation is configured in software and implemented in the card
through software download messages. When the card is idle, it provides a
high impedance toward the CO for isolation and ac (ringing) detection.
Incoming calls
The alerting signal into the System is 20 Hz (nominal) ringing sent by the CO.
When an incoming call is answered, ringing is tripped when the System
places a low-resistance dc loop across the tip and ring leads toward the CO.
See Figure 112 and Figure 113 on page 563.
Outgoing calls
For outgoing calls, the software sends an outgoing seizure message to place
a low-resistance loop across the tip and ring leads toward the CO. See
Figure 114 on page 564 and Figure 115 on page 565. When the CO detects
the low-resistance loop, it prepares to receive digits.When the CO is ready to