3com S330 Manuale Utente

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PPENDIX

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ATH

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UILDER

 S330/S310 M

ODULE

 

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PPLICATION

 O

VERVIEW

The VCM supports the following features:

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G.729A, G.726, and G.711 compression algorithms—You must configure 
the voice coding (compression) for each DS0 channel. The decompression runs 
in the same mode as the compression. In addition, the remote end must be set 
up to run the same mode as the local end—there is no auto-switching for the 
voice compression mode. For details about configuring VCM channels, see 
“Configuring VCM DS0 Channels” in Chapter 4.

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Voice activity detection—Voice packets are handled differently in the receive 
and transmit directions:

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From T1/E1 line to packet network, the host CPU constantly polls the DSP 
packet buffers for voice data. When it detects a voice packet, it 
encapsulates the packet into an FRF.11 subframe and forwards it to an 
output interface.

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From packet network to T1/E1 line, FRF.11 packets are decoded, 
demultiplexed, and sent to the DSP as soon as they are received on the PCI 
interface.

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Fax relay—Fax data is transferred using FRF.11 Fax Relay Transfer. The DSP 
detects if the fax preamble is a single frequency tone or a non-single frequency 
tone.

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If the DSP detects a single frequency preamble, it modulates the fax using 
modulation type V.21 and transfers the fax data at 300bps using T.30 fax 
payload format.

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If the DSP detects a non-single frequency preamble, it modulates the fax 
using various modulation types and transfers the fax data at 300bps to 
14400 bps using T.4 payload format.

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DTMF relay—Dialed digits are detected by the DSP and transported using 
FRF.11 Dialed Digit Payload format. The dialed digit frame is transported only 
when a DTMF tone is detected. The DTMF tone is generated by the DSP when 
dialed digits are received through the packet network.