Which of the following is not a function of MTPs?
- addressing DTMF transport mismatches
- converting between IPv4 and IPv6 RTP streams
- converting digital audio from one codec to another
- delivering SIP Early Offers over SIP trunks
Converting digital audio from one codec to another is a function of a transcoder, not of Media Termination Points (MTPs). Transcoders enable communication between devices that support dissimilar audio codecs. For example, a transcoder can translate a G.729-encoded packet to a G.711encoded packet and vice versa. Transcoders translate the data stream in real time between two devices so that no audio delay is experienced by either endpoint.
In Cisco Unified Communications systems, MTPs are used to deliver Session Initiation Protocol (SIP) Early Offers over SIP trunks. There are two ways to enable Early Offers on SIP trunks in Cisco Unified Communications Manager (UCM): select the MTP Required-check box on the SIP trunk or select the Early Offer support for voice and video calls (insert MTP if needed) check box on the SIP profile that is connected to the SIP trunk. If MTP is required, all outbound calls will use MTP, as will calls operating on the same codec. If MTP is enabled as needed, it is inserted if the trunk is incapable of sending complete information about its media capabilities in the SIP Invite message.
In addition to SIP Early Offers, MTPs are used to address dual-tone multi-frequency (DTMF) transport mismatches, to convert between IP version 4 (IPv4) and IPv6 for voice Real-time Transport Protocol (RTP) streams, to act as Resource Reservation Protocol (RSVP) agents, and to act as a Trusted Relay Point (TRP).