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Voice Modules (VCMs & DPVs)
The ADPCM or VLBRV echo canceller may be enabled or disabled by a pair of switches on the
VCM basecard. The CELP echo canceller is always enabled. The switches also allow an external
control signal to enable or disable the echo canceller when needed on a per-call basis. Either an open
or short on the external echo canceller control leads may be selected to enable the echo canceller.
The residual echo suppressor may also be enabled or disabled by means of a switch. Generally, it
should be enabled when the echo canceller is enabled.
The ADPCM echo canceller can cancel echoes with a maximum delay of 16ms. This delay is not
the circuit round-trip delay, but the delay from the echo canceller to the source of the signal
reflection - the 2W/4W hybrid. The echo canceller adapts to any echo or series of echoes in a 0-16
ms window. The delay window may be increased to 7-23 or 14-30 ms by means of the bulk delay
switches on the VCM basecard. The 0 ms setting is suitable for almost all applications.
The DPV echo canceller can cancel echoes with a maximum delay of 8ms. This delay is not the
circuit round-trip delay, but the delay from the echo canceller to the source of the signal reflection
- the 2-wire to 4-wire hybrid. Echo cancellation is designed to eliminate near-end, local loop echoes,
but also cancels any echo present within the 8 ms window.
VCM Options
The onboard options are typically set at the factory to match your network operation. Check these
settings when you first install the unit. You need not repeat the procedure unless you change your
network. The figures listed below show option switches and headers in their normal or default
(factory shipped) positions.
the Voice Channel modules.
1. Examine the module by checking the option switches and/or headers on the modules.
2. When you are satisfied that the option settings are correct, install the modules in the shelf
following the directions below.
VCM Module Installation
With the exception of the power supply modules, all plug-in modules have an insertion and
extraction tab on the bottom of the front panel.
1. To install a plug-in module, insert the module into its slot with the GDC logo on top, then slide
it in until it makes contact.
2. Pull down the insertion/extraction tab and firmly push the module in until it seats in the rear
connectors.
3. To remove a plug-in module, pull down the insertion/extraction tab to unseat the module, then
pull on the tab.
VCM Installation Restrictions
Any module may be installed in any slot, with the following restrictions:
•
Assignment of modules to slots must be that of the configuration on the TMS Controller or
OCM-1000 Point-to-Point Controller.
•
Rear panel Zone 1 (top) and Zone 3 (bottom) connector panels must meet the module
requirements.
•
The number and type of modules must not exceed the power rating of the installed power
supplies.
•
For maximum system reliability, we recommend that a module be removed from the currently
active TMS configuration before it is extracted from its slot.
036R340-000
Issue 16
Figure 6-1
shows the location and function of switches and headers on
Office Connunications Manager OCM-1000/OCM-2000
Installation & Operation
VCM Overview
6-3
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