Digital Voice Systems Net-2000-P25, Руководство пользователя

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Net-2000™ Voice Codec Unit
User’s Manual
Page 12
Section 3 – Net-2000™ VCU Control
DVSI Confidential Proprietary
Half-Rate Vocoder Mode
Net-2000™- P25 VCU Half-Rate Mode offers built-in Soft Decision Forward Error Correction (FEC)
detection, DTMF / Knox Tone Detection and generation and DTX Comfort Noise Insertion.
The Half-Rate Vocoder is DVSI’s new low data rate vocoder technology. The Half-Rate vocoder in
the Net-2000™- P25 VCU has a total data rate of 3600 bps. This new Half-Rate includes 2450 bps
of data and 1150 bps of FEC. It is designed to be particularly robust and perform exceptionally well
even under the presence of bit errors and acoustic background noise conditions.
Bit Stealing Half-Rate Vocoder Mode
This mode is identical to Half-Rate Vocoder Mode except that 300 bps of the channel data stream
can be used to transmit user data in-band.
Half Rate Vocoder Additional Features
As part of Half-Rate vocoder mode the Net-2000™ VCU offers the ability to decode up to 8 bits of
Soft Decision Forward Error Correction. This feature is ideal for testing and evaluating degraded
channel conditions and/or significant bit errors.
In addition to the enhanced FEC capability the Net-2000™ VCU Half-Rate vocoder provides voice
activity detection and DTMF Knox Tone detection and regeneration. See Section 4 Protocol for
more information.
Communication Channel Selection
The Net-2000™-P25 can be configured to encode / decode speech from either one of two
communications channel sources. The default channel is loopback. Only one communication mode
may be selected at a time. After switching from one communications mode to the other it is
necessary to select the start button in order to initiate the change.
Figure 9 Communications Menu
Loopback (Local)
In loopback communications mode the Net-2000™- P25 VCU will encode speech received on the
selected voice source input (4-Wire or Handset) and play out the encoded/decoded speech on the
handset and Line-Out interface. This channel selection is useful when encoding / decoding
recorded voice samples as a quick analysis of the selected vocoder. This selection enables VOIP
mode on the VCU.
When Loopback communications mode is selected the Net-2000™ VCU sends data over the
internal loopback Ethernet address of 127.0.0.1. Loopback can also be accessed by entering in the
IP or host name of the Net-2000™ VCU in the Target IP address box.