In Key Press Markup Language, which SIP request is used to deliver the actual DTMF digits?
KPML procedures use a SIP SUBSCRIBE message to register for DTMF digits.
The digits themselves are delivered in NOTIFY messages containing an XML encoded body.
In Key Press Markup Language (KPML), which is used for transmitting Dual Tone Multi-Frequency (DTMF) signaling information over Session Initiation Protocol (SIP) networks, the SIP request used to deliver the actual DTMF digits is the INFO request.
The INFO method is an extension method for SIP that is used to carry non-SIP related information, including KPML messages. It is defined in RFC 6086 and is used to transmit signaling information, such as DTMF digits, from the sender to the receiver.
The KPML message, which contains the DTMF digits, is encapsulated within the body of the INFO request. The receiver of the INFO request is responsible for extracting the KPML message from the body and translating it into the appropriate DTMF tones.
In contrast, the SUBSCRIBE and NOTIFY requests are used for event notification in SIP, while the INVITE and ACK requests are used for session initiation and acknowledgment, respectively. Therefore, neither of these methods is used for delivering DTMF digits via KPML in SIP.