3Com S330 manual VCM supports the following features

242APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW

Supported Voice Compression Features

The VCM supports the following features:

■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.

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

■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.

■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.

■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.

■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.

■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.

■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.