What is needed to support SIP Early Media?

SIP Early Media refers to audio (such as ringback tones, error announcements, or IVR prompts) that flows before the call is answered and a 200 OK is received. CUCM requires an MTP (Media Termination Point) to support this because it acts as a media anchor, allowing CUCM to pass early media between the originating and terminating legs of the call. Without an MTP, CUCM cannot properly handle the mid-call media path changes associated with early media negotiation.

A Transcoder converts between incompatible codecs and is not specifically required to support SIP Early Media flow.

An Annunciator plays system-generated announcements but is not involved in anchoring or passing through SIP Early Media from remote endpoints.

A Conference Bridge enables multi-party conferencing and plays no role in supporting SIP Early Media between two endpoints.

A DSP is a hardware resource used by media devices such as MTPs and transcoders, but specifying a bare DSP is not sufficient - the MTP software resource specifically is what CUCM requires for SIP Early Media.

A Route List is a call routing construct that determines the order of route groups for outbound calls and has no bearing on early media processing.