242 APPENDIX B: P ATH BUILDER S330/S310 MODULE AND A PPLICATION O VERVIEWSupported VoiceCompression FeaturesThe VCM supports the following features:n G.729A, G.726, and G.711 compression algorithms—You must configurethe voice coding (compression) for each DS0 channel. The decompression runsin the same mode as the compression. In addition, the remote end must be setup to run the same mode as the local end—there is no auto-switching for thevoice 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 receiveand transmit directions:n From T1/E1 line to packet network, the host CPU constantly polls the DSPpacket buffers for voice data. When it detects a voice packet, itencapsulates the packet into an FRF.11 subframe and forwards it to anoutput 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 PCIinterface.n Fax relay—Fax data is transferred using FRF.11 Fax Relay Transfer. The DSPdetects if the fax preamble is a single frequency tone or a non-single frequencytone.n If the DSP detects a single frequency preamble, it modulates the fax usingmodulation type V.21 and transfers the fax data at 300bps using T.30 faxpayload format.n If the DSP detects a non-single frequency preamble, it modulates the faxusing various modulation types and transfers the fax data at 300bps to14400 bps using T.4 payload format.n DTMF relay—Dialed digits are detected by the DSP and transported usingFRF.11 Dialed Digit Payload format. The dialed digit frame is transported onlywhen a DTMF tone is detected. The DTMF tone is generated by the DSP whendialed digits are received through the packet network.
