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rangement). Each station handsets should be used adjacent to the speaker
which is muted by its "press to talk'' button. Other live speakers connected
to the same network may provide a feedback path (an echo).
In any network it is necessary that you put into place a Loss Plan. A Loss
Loss Plan
Plan is the design of the TLPs in the network. The Loss Plan is one
method by which you may limit the effects of echo and other line related
problems. The Loss Plan also assures that all parties using the system
are assured quality lines.
Each of the devices in the network has some nominal operating TLP.
Most equipment is adjustable, but many have fixed TLPs. It is important
that you set up pieces of equipment to compatible levels.
The Loss Plan records the levels at each interface when a 0 dBm0 tone is
being sent from one end to the other. The levels may be different in either
direction.
An example of a Loss Plan for a very simple circuit is two 4-wire
telephones connected back to back via a CELP link:
(0)
0
PHONE
A
0
(0)
The figures at each interface indicate the signal level relative to a 0 TLP
at each telephone output. The figures in parentheses indicate the gain
through each section in dB.
If, in our example, Phone B was connected via a long "tail'' circuit with 1
dB of signal loss in each direction, then +1 dB of gain would need to be
added either at the telephone or at the CELP to compensate for this loss. In
the following example we have chosen to add the 1 dB of gain at the CELP
transmit and receive sections. The Loss Plan is modified as follows:
(0)
0
PHONE
A
0
(0)
(0)
0
CELP
MUX
A
NETWORK
0
(0)
(0)
0
CELP
MUX
A
NETWORK
0
(0)
(0)
(0)
0
CELP
B
(0)
0
(0)
036R480DE
(+1)
+1
(–1)
CELP
B
(+1)
–1
(–1)
APPENDIX D
0
PHONE
B
0
0
PHONE
B
0
036R480DF
D-13
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