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242 APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW
Supported Voice
Compression Features
The VCM supports the following features:
n 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.
n Voice activity detection—Voice packets are handled differently in the receive
and transmit directions:
n 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.
n 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.
n 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.
n 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.
n 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.
n 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.