<abstract>This specification defines an XML format for encapsulating Dual Tone Multi-Frequency (DTMF) events in informational messages sent within the context of Jingle audio sessions, e.g. to be used in the context of Interactive Voice Response (IVR) systems.</abstract>
<remark><p>Removed negotiation flow so that this specification describes only the XMPP transport of DTMF events; added error flows to be used if the code is not understood or if a non-XMPP method is preferred.</p></remark>
</revision>
<revision>
<version>0.8</version>
<date>2008-03-20</date>
<initials>psa</initials>
<remark><p>Clarified negotiation flow; added payload-types per RFC 4733.</p></remark>
<remark><p>Updated syntax to use action and code attributes rather than tone element in order to provide real-time interaction; specified how to negotiate use of the RFC 4733 format via content-info messages.</p></remark>
<p>Traditional telephony systems use Dual Tone Multi-Frequency (DTMF) events for dialing and to issue commands such as those used in Interactive Voice Response (IVR) applications. Internet telephony systems also use DTMF tones for interoperability with the public switched telephone network (PSTN).</p>
<p>If XMPP application use &xep0166; for voice chat (see &xep0167;) and wish to exchange DTMF events, they MUST support the protocol described in this document. However, they MAY also support non-XMPP methods of communicating DTMF information, such as the "audio/telephone-event" and "audio/tone" media types as sent over the Real-time Transport Protocol (&rfc3550;).</p>
<p>The <dtmf/> element SHOULD possess an 'action' attribute, the value of which MUST be either "button-up" or "button-down" (specifying whether the button is being depressed or released). This enables DTMF tones to be reconstructed in real time. If the 'action' attribute is not included, the recipient MUST assume that the action is a "button-down" event.</p>
<p>Unless the 'action' attribute has a value of "button-up", the <dmtf/> element MUST possess a 'code' attribute that specifies the tone to be generated. The value of the 'code' attribute SHOULD be one the following characters: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, #, and * (however, the characters A, B, C, and D MAY be sent as well <note>Although A, B, C, and D were originally defined as part of DTMF, they were never deployed to telephony consumers and were used only for control purposes at private branch exchanges (PBXs) and central office operator stations; however, they are used in certain non-telephony applications of DTMF, such as ham radio.</note>).</p>
<p>The OPTIONAL 'duration' attribute specifies indicates the duration of the event, in milliseconds, expressed as an unsigned integer. The receiver SHOULD ignore the event if the 'duration' value is zero. If the 'duration' attribute is not included and the event is explicitly or implicitly a "button-down" event, the recipient MUST assume that the event expires after a reasonable timeout (100 milliseconds is RECOMMENDED) or when a "button-up" event is received, whichever comes first.</p>
<p>The OPTIONAL 'volume' attribute specifies the power level of the tone, expressed in dBm0 after dropping the sign. Power levels range from 0 to -63 dBm0. Thus, larger values denote lower volume.</p>
<p>If the receiving entity is using or wishes to use a different method for exchanging DTMF events (e.g., the methods specified in &rfc2833; or its successor &rfc4733;), it MUST return a ¬acceptable; stanza error.</p>
<p>If an entity supports Jingle DTMF (i.e., sending of DTMF in the XMPP signalling channel as specified herein), it MUST return a &xep0030; feature of "urn:xmpp:tmp:jingle:dtmf" in response to service discovery information requests. Naturally, support MAY also be determined via the dynamic, presence-based profile of Service Discovery defined in &xep0115;.</p>
<p>Until this specification advances to a status of Draft, its associated namespace shall be "urn:xmpp:tmp:jingle:dtmf". Upon advancement of this specification, the ®ISTRAR; shall issue a permanent namespace in accordance with the process defined in Section 4 of &xep0053;. The following namespace is requested, and is thought to be unique per the XMPP Registrar's requirements: "urn:xmpp:jingle:dtmf".</p>
