Nortel Networks Circuit Card 311 User Manual

Page 157

Application

157

regulatory requirements as well as industry standards, they are not
designed to compensate for modified ICL designs in the connecting
facilities.

•

Nortel Networks recommends that the attenuation distortion (frequency
response) of the OPS facility be within ±3.0 dB over the frequency
range from 300 to 3000 Hz. It is desirable that this bandwidth extend
from 200 to 3200 Hz.

•

The terminating impedance of the facility at the OPS port be
approximately that of 600 ohms cable.

If the OPS line facility loss is greater than 4.5 dB but does not exceed 15
dB, line treatment using a switched-gain Voice Frequency Repeater (VFR)
extends the voice range.

The overall range achievable on an OPS line facility is limited by the
signaling range (2300 ohms loop including telephone set resistance). The
signaling range is unaffected by gain treatment; so gain treatment can
be used to extend the voice range to the limit of the signaling range. For
example, on 26 AWG wire, the signaling range of 2300 ohms corresponds
to an untreated metallic loop loss of 15 dB. Gain treatment (such as a VFR)
with 10.5 dB of gain would maintain the OPS service loss objective of 4.5
dB while extending the voice range to the full limit of the signaling range.

15 dB
–4.5 dB

= 10.5 dB

The use of dial long line units to extend signaling range of OPS analog line
cards beyond 15 dB is not recommended.

Termination transmission characteristics

The loss plan for OPS connections is designed so that a connection with an
OPS termination provides satisfactory end-to-end listener volume when the
OPS termination is a standard telephone. The listener volume at the distant
end depends on the OPS termination transmit loudness characteristics;
the volume at the OPS termination end depends on the OPS termination
receive loudness characteristics.

A feature of many (though not all) standard telephones is that the loudness
increases with decreased current. So as the line (PBX to OPS termination)
facility gets longer and loss increases, the increased loudness of the
telephone somewhat compensates for the higher loss, assuming direct
current feed from the PBX with constant voltage at the feeding bridge.
However, this compensation is not available when:

•

the termination is a non-compensating telephone

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311

01.04

Standard

Release 5.0

23 May 2008