3.1 Common Details

In [RFC4733], out-of-band negotiation of telephony signal information is required to establish a session. During this negotiation, both payload types and the clock rate of the telephony signals are negotiated as described in [RFC4733] section 2.5.1.1 using SDP for out-of-band negotiation. While dynamic payload type binding is required, both the sender and receiver of message blocks conforming to RTPDT MUST fix the telephony signaling information at 8,000 Hertz. Dynamic negotiation of the clock frequency of the DTMF payload MUST NOT be used.

[RFC4733] allows a "zero" duration in the payload of an RTP packet for state events. Endpoints using RTPDT MUST NOT send telephony events with a "zero" duration. Telephony events include the state and nonstate events.

All event duration values MUST NOT exceed the maximum duration expressible in the duration field of the payload format as described in [RFC4733] section 2.3.5.

Redundancy support as described in [MS-RTPRAD] MUST NOT be used. Integrity for the payload is not defined by this specification; see [MS-RTPRAD] section 2.2 for payload integrity information.

Multiple payload type binding for different telephony events MUST NOT be used. There MUST be only one telephony event binding for a payload type. The payload type binding MUST be symmetrical. This means the receive payload type and send payload type MUST be the same. Asymmetrical payload type information MUST NOT be used.

RTPDT supports only the telephony event. An in-band telephony tone transmission MUST NOT be used.

All clock frequencies for DTMF signals, tones, and digits MUST be fixed at 8,000 Hertz.