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System Overview
2-3
The Voice II/CVSD channel module uses Continuously Variable Slope Delta (CVSD) modula-
tion techniques to perform voice-to-data and data-to-voice conversions. The term CVSD is used
in all supervisory port inter-face displays to refer to the Voice II/CVSD module. The Voice II/
CVSD Channel can operate using a range of data rates from 14.4 kbps to 64.0 kbps.
The Voice II/PCM and Universal Voice Card/PCM modules use standard Pulse-Coded Modula-
tion for voice-to-data and data-to-voice conversions. The modules provide G.711 coding and
comply with CCITT G.712 performance specifications. These modules operate at a fixed rate of
64 kbps (66 kbps of aggregate bandwidth is actually used by a PCM channel to allow for trans-
mission of synchronization and overhead bits). A PCM channel provides slightly better voice re-
production than a CVSD channel, and is therefore more reliable when used in a tandem TDM
network (up to 10 sequential TDM links).
The Voice II/ADPCM module is the PCM module with an ADPCM piggyback card mounted on
the PCM card. The term ADPCM is used in all supervisory port interface displays to refer to the
Voice II/ADPCM Voice Channel module. Standard ADPCM (Adaptive Differential Pulse-Coded
Modulation, as described by CCITT Specification G.721) techniques allow a data rate of 32 kHz
(34 kHz of aggregate bandwidth is actually used by the module). The ADPCM channel provides
slightly better voice reproduction than a CVSD channel operating at 32 kHz, and is therefore
more reliable when used in a tandem TDM network (up to 4 sequential links).
Either the Voice II/PCM or the Voice II/ADPCM Voice Channel module may also include an
EAM (E and M) piggyback card. This card allows the module to support E and M signaling (for
applications outside of the United States, a version of the PCM or ADPCM Voice Channel will
support British Telecom DC5 signaling). The EAM piggyback card also supplies diagnostic ca-
pabilities not provided by the Voice II/PCM or Voice II/ADPCM modules alone.
The fixed rate Voice II/ASP Channel module is an analog basecard with a piggyback card. Two
modes are used by the supervisory port interface display to refer to the Voice II/ASP Channel
module. They are ASP and PCM-T. The ASP mode converts 64 kbps PCM voice data to 16 kbps
ASP voice data for insertion into the aggregate stream. The PCM-T mode bypasses the ASP al-
lowing 64 kbps PCM voice data into the aggregate stream.
The Voice II/ASP (Variable rate version), when installed in conjunction with the Universal
AUTO FRAME module, provides variable rate ASP at rates of 10 kbps, 11 kbps, 12 kbps and 16
kbps.
The Universal Voice Card/ADPCM used in conjunction with the Universal AUTO FRAME mod-
ule includes integral E and M circuitry and provides variable rate ADPCM. The data rate and the
voice encoding scheme are software selectable.
036R660-000, Issue 10
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