Nortel NT1R20 Description page 97

NT1R20 Off-Premise Station Analog Line Card
Termination transmission characteristics
The loss plan for OPS connections is designed so that a connection with an
OPS termination will provide satisfactory end-to-end listener volume when
the OPS termination is a standard telephone set. The listener volume at the
distant end depends on the OPS termination transmit loudness characteristics,
and the volume at the OPS termination end depends on the OPS termination
receive loudness characteristics. With standard telephone sets, these
characteristics are such that satisfactory—if not optimum—performance is
achievable within the above noted objectives for connecting facilities.
A feature of many (though not all) standard telephone sets is that the loudness
increases with decreased current. Thus, as the line (Meridian 1 to OPS
termination) facility gets longer and lossier, the increased loudness of the set
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 following occurs:
— the termination is a non-compensating telephone set
— the OPS port is served by a line card using a constant-current feeding
bridge
— the OPS termination is to telephone sets behind a local switch providing
local current feed, such as a key telephone system
OPS line terminations with loudness characteristics designed for other
applications may also impact transmission performance. For example,
wireless portables loudness characteristics are selected for connections to
switching systems for wireless communication systems; if deployed in an
OPS arrangement without due consideration for these characteristics, the
result could be a significant deviation from optimum loudness performance.
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Line cards Description