Nortel NT1R20 Description page 96

Page 72 of 290 NT1R20 Off-Premise Station Analog Line Card
553-3001-105 Standard 5.00 June 1999
The following requirements are based on historic inserted connection
loss (ICL) objectives:
• PBX–CO trunk: 5 dB with gain; 0–4.0 dB without gain
• OPS line: 4.0 dB with gain; 0–4.5 dB without gain
In recent times economic and technological considerations have led to
modifications of these historic objectives. However, the loss provisions
in the PBX for OPS are constrained by regulatory requirements as well
as industry standards; thus, they are not designed to compensate for
modified ICL designs in the connecting facilities.
— The attenuation distortion (frequency response) of the OPS facility
should 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 should
approximate that of 600 ohm 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) will
extend the voice range.
The overall range achievable on an OPS line facility is limited by the
signaling range (2300 ohm loop including telephone set resistance). Signaling
range is unaffected by gain treatment; thus, gain treatment can be used to
extend the voice range to the limit of the signaling range. For example, on
26AWG 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:
15.0 dB
– 4.5 dB
= 10.5 dB
The use of dial long line units to extend the signaling range of OPS analog
line cards beyond 15 dB is not recommended.
(loss corresponding to the maximum signaling range)
(OPS service loss objective)
(required gain treatment)