Information Technology Reference
In-Depth Information
Media Termination Points
An MTP can bridge together two full-duplex voice streams, and (if necessary) convert between G.711 mu-law and a-law as well as
different sample sizes. An MTP can also be used for dual-tone multifrequency (DTMF)
conversion and for other specific protocol
uses such as H.323 supplementary services, H.323 outbound fast connect, and SIP early offer.
Each of the voice streams that the MTP bridges together are set up and torn down independently of each other, thus allowing the
H.323 supplementary services to be supported. If CUCM attempts to allocate an MTP but cannot, it attempts to directly connect the
endpoints.
MTP can be used to provide supplementary service capabilities, such as hold, transfer, Call Park, and conferencing to H.323v1
devices that otherwise would not be able to support these features. H.323v1 devices cannot support these supplementary services
natively because they lack support for the H323v2 OpenLogicalChannel and CloseLogicalChannel requests with Empty Capabilities
Set (ECS).
Note that CUCM 4.x needs an RFC 2833-compliant MTP to make SIP calls using DTMF call signaling tones. An RFC
2833-compliant MTP translates between the out-of-band DTMF tones used by SCCP and SIP in-band (payload type) DTMF tones.
CUCM 5.x and later remove the requirement for an MTP when supporting RFC 2833 DTMF. CUCM supports software MTPs using
the Cisco IP Voice Media Streaming Application, Cisco IOS software MTPs, and hardware MTPs.
Software MTPs that are based on Cisco IP Voice Media Streaming Application support RFC 2833 DTMF relay and G.711; Cisco IOS
software MTPs support G.711, G.729, G.729a, G.729b, G.729ab, and GSM, but with only one of these codecs configured at a time;
and hardware MTPs support (depending on the specific hardware) G.711, G.729, and G.729b.
Software MTPs using the Cisco IP Voice Media Streaming Application support 48 MTP resources (by default), Cisco IOS software
MTPs support 500 streams (250 transcoded sessions), and hardware MTPs support a variety of session totals, depending on specific
hardware.
