DTMF-Relay
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There are 3 common ways of relaying DTMF: | There are 3 common ways of relaying DTMF: | ||
| − | #[http://www.ietf.org/rfc/rfc2833.txt RFC2833] | + | #[http://www.ietf.org/rfc/rfc2833.txt RFC2833] |
#SIP INFO | #SIP INFO | ||
| − | #In Band | + | #In Band<br> |
| − | + | ||
| − | <br> | + | |
== RFC2833 == | == RFC2833 == | ||
| − | + | [http://www.ietf.org/rfc/rfc2833.txt RFC2833] is the prefered method for relaying, where the in-call DTMF are removed from the in-band voice, and are sent to the peer over the RTP stream, as specially marked packet. | |
This method also offers a robustness against packet losses by using redundancy scheme. | This method also offers a robustness against packet losses by using redundancy scheme. | ||
| − | RFC2833 is usually being handled by VoIP hardware, and requires no CPU intervention. | + | RFC2833 is usually being handled by VoIP hardware, and requires no CPU intervention. |
== SIP INFO == | == SIP INFO == | ||
| − | |||
| − | |||
The SIP INFO method can be used by SIP network elements to transmit DTMF tones out-of-band as telephone-events in a reliable manner independent of the media stream. | The SIP INFO method can be used by SIP network elements to transmit DTMF tones out-of-band as telephone-events in a reliable manner independent of the media stream. | ||
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In the DTMF relay method the body of the SIP message consists of signaling information and uses the content-type application/dtmf-relay | In the DTMF relay method the body of the SIP message consists of signaling information and uses the content-type application/dtmf-relay | ||
| − | + | This method can be used where peer VoIP doesn't support RFC2833. This method relies on CPU power to relay the DTMF. | |
| + | |||
| + | == In Band == | ||
| + | |||
| + | In-band is used when the two other methods aren't available. The DTMF is relay with in-band voice, and is more likely to work on lossless codecs, like G.711. | ||
| + | |||
| + | |||
| + | |||
| + | == Toolpack DTMF-Relay == | ||
| + | |||
| + | Toolpack gateway relay scheme is: | ||
| + | |||
| + | | ||
Revision as of 08:59, 17 March 2010
Contents |
Dual-tone Multi-frequency Relay
Dual-tone Multi-frequency Relay (DTMF) is the mechanism where a VoIP gateway listens for in-call tones, and relay them to the peer according to the negotiated method.
Relaying DTMF prevents loosing its signal integrity over VoIP compressed codecs. The relayed DTMF is then being regenerated transparently on the peer side.
There are 3 common ways of relaying DTMF:
- RFC2833
- SIP INFO
- In Band
RFC2833
RFC2833 is the prefered method for relaying, where the in-call DTMF are removed from the in-band voice, and are sent to the peer over the RTP stream, as specially marked packet.
This method also offers a robustness against packet losses by using redundancy scheme.
RFC2833 is usually being handled by VoIP hardware, and requires no CPU intervention.
SIP INFO
The SIP INFO method can be used by SIP network elements to transmit DTMF tones out-of-band as telephone-events in a reliable manner independent of the media stream.
In the DTMF relay method the body of the SIP message consists of signaling information and uses the content-type application/dtmf-relay
This method can be used where peer VoIP doesn't support RFC2833. This method relies on CPU power to relay the DTMF.
In Band
In-band is used when the two other methods aren't available. The DTMF is relay with in-band voice, and is more likely to work on lossless codecs, like G.711.
Toolpack DTMF-Relay
Toolpack gateway relay scheme is:
