Rfc2833 Dtmf Digit Transmission; Info-Based Dtmf Digit Transmission - Alcatel-Lucent 7302 Information Manual

5 — VoIP overview

RFC2833 DTMF digit transmission

Inband transmission of DTMF tones only occurs when digit collection is not being
performed. This inband transmission provides a way for a server to independently
collect dialed digits, allowing the ONT to pass them transparently. By comparison,
RFC2833 transmission of DTMF is an alternative method of transmitting DTMF
digits.
In VoIP processing, the use of RFC2833 is a negotiated item in the Session
Description Protocol (SDP). The SDP Offer/Answer negotiation is used to determine
if the two endpoints should actually use RFC2833 transmission or not.
When using the RFC2833 transmission method, digits are encoded in
RFC2833-defined packets so the server does not have to decode RTP packets in
order to process DTMF tones. When RFC2833 packets are used for DTMF
transmission, the DTMF tones are not sent in the encoded RTP data.
The 7360 ISAM FX provides a provisioning option to enable or disable this feature
so the ONT knows whether or not to initiate offers with RFC2833 or not. See the SIP
provisioning parameter enable_rfc2833 in Table 5-13.

INFO-based DTMF digit transmission

As an alternative to RFC2833 DTMF transmission, the ONT supports sending and
receiving DTMF digits in SIP INFO messages. The digit is represented in the body
of the INFO messages following a content type header of
application/telephone-event as follows:
Content-Type: audio/telephone-event
Content Length: 4
xxyyyyyy
Where xxyyyyyy is a 32-bit value. xx is the top-most 8 bits, and yyyyyy is the next 24
bits. xx represents one of the 16 possible DTMF event values specified in RFC2833
(0 through 15). yyyyyy is not used, it will be ignored in INFO messages received, and
set to 0 for INFO messages generated by the ONT.
As with RFC2833 DTMF transmission, a digit sent with this method will not be sent
in the encoded RTP voice data. INFO based DTMF transmission is enabled with the
enable_info_based_dtmf parameter from Table 5-13.
5-80 November 2013
Note —
This feature does not change how pulse dialing is handled,
and applies to DTMF only. INFO-based DTMF digit transmission
does not apply to Package D or I-240W-S ONTs
Note —
This feature does not change how pulse dialing is handled,
and applies to DTMF only.
Alcatel-Lucent 7302 ISAM | 7330 ISAM FTTN | 7360 ISAM FX ONT R04.06.02
Edition 01 3FE 55873 AAAA TCZZA
ONT Product Information Guide