Configuring The Dtmf Transport Types - AudioCodes Mediant 1000 User Manual

8.2

Configuring the DTMF Transport Types

The Mediant 1000 gateway supports several methods of conveying DTMF digits over the
IP network. Three methods are controlled by H.245 protocol and therefore use its capability
exchange mechanism to ensure coordination with the remote side. A fourth method uses
Q.931 Info messages. If neither of these methods is selected, DTMF is transferred inside
the audio stream.
The Mediant 1000 gateway supports the following DTMF transfer methods (the first three
methods use H.245 capability exchange):
RFC 2833 - DTMF digits are relayed to the remote side as part of the RTP stream
according to the RFC 2833 standard. The H.245 capability exchange coordinates the
source and destination payload types. The gateway's received packets' RFC 2833
payload type is configured by the parameter RFC2833PayloadType (default 96); the
gateway's transmitted payload type is identical to the payload type received from the
remote party.
H.245 Signal – Out-of-Band DTMF using H.245 UserInfo messages (refer to the note
below).
H.245 User Input - Out-of-Band DTMF, similar to H.245 Signal, but without DTMF
length reconstruction (refer to the note below).
Q.931 Info Message – (without H.245 negotiation): Similar to H.245 User Input but
over Q.931. This method is not included in the H.245 capabilities exchange and
therefore, when selected, is always used.
The gateway's DTMF transfer mechanism ensures that only a single DTMF digit is
generated. The mechanism erases all digits from the audio stream. This solves the
problem of double detection (caused as a result of different paths of DTMF) at the remote
side.
If none of the above transfer methods is used, DTMF digits can be sent as part of the audio
stream (in RTP packets). This is normally used with G.711 coders; with other Low Bit Rate
(LBR) coders the quality of the DTMF digits is reduced. Set the parameter
DTMFTransportType to 'Transparent' for DTMF to not be removed from the voice stream.
Note:
To configure the gateway DTMF transfer type:
Set the preferred Transmit DTMF methods using the
1.
DTMF negotiation methods are prioritized according to the order of their appearance.
Set the supported Receive DTMF negotiation method using
2.
To configure the gateway to convey DTMF digits in the audio
stream:
Ensure that neither of the following parameters is configured (set to 'not supported'):
1.
DTMFTxOptions, DTMFRxOption.
Set parameter DTMFTransportType = Transparent (2).
2.
H.323 User's Manual
When Fast Start is used the H.245 channel remains close, therefore out-of-
band signaling can't be used, unless the remote side opens the H.245
channel or the Mediant 1000 is configured to open H.245 on Fast Start.
260
Mediant 1000
table. Note that
TxDTMFOption
parameter
RxDTMFOption
Document #: LTRT-83401
.