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Voice Modules (VCMs & DPVs)
Chapter 6:
VCM Overview
On the transmission side, Voice Channel Modules (VCMs) convert voice grade signals to digital
data for transmission through the system and convert the digital data to voice signals on the receive
side. FXO, FXS, and E&M signaling can be provided by separate plug-in cards. FXS and FXO
modules are 2-wire interfaces, while E&M modules can be either 2-wire or 4-wire.
Several versions of the Voice Channel Module are available
respect to compression algorithms and signaling. Some choices for signaling are 4-wire E&M, 2-
wire E&M, 2-wire FXS and 2-wire FXO. The analog 2-wire voice capability is used to support 2-
wire to 4-wire (loop start and ground start) interconnections.
Voice Channel Modules support PCM, ADPCM and VLBRV encoding algorithms. ADPCM rates
are the same as those supported by the UVC, for example, 64 kbps PCM, and 32 kbps, 24 kbps and
16 kbps ADPCM. Each ADPCM voice channel includes 800 Hz of signaling overhead. The
VLBRV supports the same operating rates (9.6/4.8 kbps) as the existing TMS VLBRV card. FAX
Bypass remains an option. The OCM VLBRV module requires no additional bandwidth for
signaling, which is done in-band.
Voice Channel Modules provide the following additional features:
•
Compliance with FCC part 68 requirement
•
End-to-end compatibility with UVC/ADPCM, UVC/VLBRV, and CELP terminations in
TMS
•
ADPCM encoding compatible with ITU-T G.721 at 32 kbps, and GDC proprietary
ADPCM encoding at 32, 24, and 16 kbps
•
Programmable transmit and receive levels
•
Internally generated ringing and battery for short loops
•
Optionally, external battery and ringing for long loops
036R340-000
Issue 16
Office Connunications Manager OCM-1000/OCM-2000
Installation & Operation
(Table
1-1). These versions differ with
6-1
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