SIP DTMF Transmission

Last Updated : Apr 27, 2022 |

DTMF key presses can be transmitted either in-band as audio tones or signaled using DTMF over RTP (RFC 2833)

When using DTMF over RTP (RFC 2833), the IP Office supports asymmetric dynamic payload negotiation when it is necessary to bridge SIP endpoints that do not support payload negotiation. The value used for an initial offer is configured on the System | Codecs tab. The default value is 101. Upon receipt of an offer with an RFC2833 payload type, IP Office automatically uses the proposed value rather than its own configured value. This helps to support networks that do not negotiate payload types.

Direct Media Calls

There are cases in which direct media is desirable between SIP trunks and endpoints that do not support RFC2833. To allow for this, if a key presses is indicate from the extension, the IP Office temporarily switches the call back to indirect media. It then injects the digits in-band using the negotiated dynamic payload and, after fifteen seconds of no further key presses, the call is switched back to direct media.

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