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An example of the use of the terms (dBm0 and TLP) would be as follows:
Picture yourself at a TMS-3000 location, about to test a voice circuit with
someone else at the other end of the voice circuit. He may ask you to in-
ject a 1004 Hz tone at a 0 dB level, so he can check his receive level. The
level that you should inject would be a level that will provide a 0 dBm
signal into the CODEC chip of your voice channel module. You would
then refer to the information about the terminal equipment and obtain the
nominal output level. You would then determine what the coarse and fine
attenuation/gain option settings are on the Voice channel module. The
tone would be injected at a level that corresponds to the nominal input
level (or TLP). The injected VF signal would be at the 0 dBm0 level.
Bridge
A device used for the interconnection of two or more
full duplex voice circuits in such a way as to allow
simultaneous transmission and reception to/from all
termination points on the circuit. The bridge is used to
insure proper level control and impedance matching.
CELP
Codebook Excited Linear Predictive. A module manu-
factured for use in General DataComm Multiplexers.
CODEC
A circuit which creates a PCM code signal from an
analog or VF waveform.
dB
The logarithmic unit of signal ratio expressed as a di-
mensionless
absolute value but instead a related loss or gain
between two points.
dBm
The actual power level of the VF signal. A power ratio
expressed in dB referred to one milliwatt; employed in
communication work as a measure of absolute power
values. 0 dBm = 1 milliwatt. This value needs to be
evaluated with reference to the TLP of the point which
is being measured.
dBm0
dB measured relative to the TLP. VF signal power ex-
pressed in dB referred to a zero transmission level
point (TLP). The VF signal, in dB after adjustment
for the TLP; dBm minus the TLP is the dBm0.
Dealer Desks
One of many types of
Dealer desks most often have
telephone
microphones.
DEMARC
The point of demarcation between the telephone
company
interconnection between any two pieces of equipment.
quantity.
This
does
voice
key
system
equipment,
and customer equipment. The point of
APPENDIX D
not
imply
any
terminal
equipment.
a
combination
of
speakers
and
D-5
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