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The Multimedia Telephony Service for IMS (MTSI), which is also referred to known as Multimedia Telephony is a standardized IMS telephone service in 3GPP. The objective of defining a service is to specify the minimum set of capabilities required in the IP Multimedia sub-system to secure multi-vendor and multi-operator inter-operability for Multimedia Telephony and related Supplementary Services.

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• MGCF providing interworking between an MTSI client and a non-MTSI client (that is, a CS UE).
• Access SBC media gateway.

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Adaptive Multi-Rate (AMR) Support

Spacevars
0 series4

SBC supports AMR Initial codec mode as per 3GPP26.114 specification. When AMR or AMR-WB is used, to avoid congestion on the link and to improve inter-working with CS GERAN, SBC limits the initial codec mode for a session to a lower mode until at least one frame-block. This feature is  configurable by ePSX flag "Initial codec mode as per 3GPP26.114". If enabled by ePSX, an AMR call starts with a lowest mode rate or second lowest mode rate until it receives a CMR request from the U.E to adapt the mode rate to a different value. If disabled, the AMR call starts with the highest mode rate within the negotiated mode-set.

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• AMR to AMR transcoding for both restricted and unrestricted mode set
• AMR to non-AMR transcoding
• AMR attributes such as mode-change-period, mode-change-capability and mode-change-neighbor.

 

Note
SBC does not support the following AMR attributes: CRC Robust-Sorting Interleaving

Note
The existing DSPs support CMR interpretation and updating the transmission rate according to peer's CMR requests.

Note
The Synchronization info attribute does not transparently pass during the transcoded and pass-through calls.

Info
For a configuration example, see Configuring AMR/AMR-WB Options.

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Real-Time Transport Control Protocol (RTCP) Support

Spacevars
0 series4

Sonus SBC supports RTCP bandwidth interworking by negotiating RR and RS bandwidth parameters. However, SBC does not allow using RTCP in a peer-to-peer voice call. This can be disabled at the MTSI client by setting RS=0 and RR=0 during call setup. But when a call is HELD, MTSI clients can enable RTCP to prevent the triggers of RTP inactivity.

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