SUBSCRIBE and NOTIFY Method for DTMF Detection


The CSP supports the SUBSCRIBE and NOTIFY methods.

If the remote SIP end points cannot multi-unicast the RFC 2833 stream, you can use the SIP SUBSCRIBE/NOTIFY method. This feature supports sending DTMF notifications via signaling.

The CSP is a subscriber and the remote end point is a notifier.

Pertinent Specification

RFC 3265


This feature works as follows:

1. When the host application issues a DTMF detection request in the DSP Service Request (0x00BD) message for a SIP call, the CSP tries to initiate a subscription for telephone events with the remote end point using the SUBSCRIBE method.

2. When the SIP remote end point accepts the subscription, the end point starts to report the digits in the SIP NOTIFY request.

3. The CSP reports these digits to the host application in the Call Processing Event (0x002E) message.

4. The host application can terminate a subscription by sending a DSP Service Cancel Request (0x00BE) message or by releasing the call.

5. At any time, a remote SIP endpoint can terminate an active subscription by sending a NOTIFY method with the "Subscription-State" header set to "terminated."

Subscribe and Notify Call Flow