Fax & Modem Transport Modes; Fax/Modem Settings - 3Com VCX v7111 User Manual

the RFC 2833 payload type using local and remote SDP and sends packets using the PT
from the received SDP. The gateway expects to receive RFC 2833 packets with the
same PT as configured by the RFC2833PayloadType parameter. If the remote side does
not include telephony-event in its SDP, the gateway sends DTMF digits in transparent
mode (as part of the voice stream).
Sending DTMF digits (in RTP packets) as part of the audio stream (DTMF Relay is
3
disabled):
Note that this method is normally used with G.711 coders; with other LBR coders the
quality of the DTMF digits is reduced.
To ser this mode:
TxDTMFOption = 0 (1
RxDTMFOption = 0 (Declare RFC 2833 in SDP = No)
DTMFTransportType = 2
The gateway is always ready to receive DTMF packets over IP, in all possible
transport modes: INFO messages, NOTIFY and RFC 2833 (in proper payload type)
or as part of the audio stream.
To exclude RFC 2833 Telephony event parameter from the gateways SDP, set
RxDTMFOption = 0 in the ini file.
The following parameters affect the way the V7111 SIP handles the DTMF digits:
TxDTMFOption, RxDTMFOption and RFC2833PayloadType (described in
MGCPDTMFDetectionPoint, DTMFDigitLength and DTMFInterDigitInterval
DTMFVolume and DTMFTransportType
Fax & Modem Transport Modes

Fax/Modem Settings

Users may choose to use one of the following transport methods for fax and for each modem
type (V.22/V.23/Bell/V.32/V.34):
Fax relay: demodulation / modulation
Bypass: using a high bit rate coder to pass the signal
Transparent: passing the signal in the current voice coder
When the fax relay mode is enabled, distinction between fax and modem is not immediately
possible at the beginning of a session. The channel is therefore in Answer Tone mode until a
distinction is determined. The packets being sent to the network at this stage are T.38-
compliant fax relay packets.
252
st th
to 5 DTMF Option = Disable)
(DTMF Transport Type = Transparent DTMF)
(Table
3Com
56).
®
VCX V7111 VoIP Gateway User Guide
Table 22).
(Table 59).