Supported Voice Compression Features - 3Com SuperStack II PathBuilder S330 Reference Manual

268 A B: P B
PPENDIX ATH UILDER
Supported Voice
Compression Features
S330/S310 M A
ODULE AND PPLICATION
The VCM supports the following features:
G. 165, G. 711, G. 726, and G.729A, 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 "The following subsections describe the VCM
configuration tasks in greater detail. For details about configuring virtual
circuits for the VCM, see "Configuring Virtual Circuits" later in this chapter." 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/Modem detection — Fax and modem signals are detected by the DSPs.
After a DSP informs the host CPU of the start of a fax or modem signal, the
host commands the DSP to switch to either 64kbps PCM or 40kbps ADPCM.
The DSP remains in this mode as long as the fax or modem call is still active.
The DSP informs the host of the end of the fax or modem call, and the host
then commands the DSP to switch back to regular voice mode with the
configured Voice Coding scheme. For details about configuring the voice
coding scheme, see "Configuring VCM DS0 Channels" in Chapter 4.
Fax Relay was supported in PathBuilder S330/S310 Release 2.03, but it is not
supported in Release 2.04.
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.
O
VERVIEW