In this section:
Modified: for 6.2.1
The Multimedia Telephony Service for IMS (MTSI), which is also 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.
The user experience of multimedia telephony is equivalent to or better than corresponding circuit-switched telephony services. Multimedia telephony also exploits the richer capabilities of IMS. In particular, multiple media components can be used and dynamically added or dropped during a session.
The MTSI client functionality is required when the SBC is deployed as:
SBC Core 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, the SBC limits the initial codec mode for a session to a lower mode until at least one frame-block. On enabling "Initial codec mode" while creating AMR Codec Entry, 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.
The SBC also supports the following functionality:
mode-change-period
, mode-change-capability
and mode-change-neighbor
.The SBC does not support the following AMR attributes:
The existing DSPs support CMR interpretation and updating the transmission rate according to peer's CMR requests.
The Synchronization info attribute does not transparently pass during the transcoded and pass-through calls.
For a configuration example, see Configuring AMR/AMR-WB Options.
The SBC Core supports RTCP bandwidth interworking by negotiating RR and RS bandwidth parameters. However, the 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.
The SBC supports enabling the RTCP for point-to-point calls only when the call is HELD based on the PSX configuration flag.
For a configuration examples, see Configuring RTCP to Support Held Calls Using RR and RS Bandwidth Modifiers.
The SBC supports:
enableRTCPForHeldCalls
and terminationForPassthrough
must be disabled on both the route PSPs.The SBC includes RR and RS values in the outgoing SDP if the IPSP flag sendRTCPBandwidthInfo
is enabled and RR and RS attributes are received from the peer.
The SBC computes RR/RS values as described below:
For I/T-SBC transcoded calls, the SBC sends answer to UAC with the RR/RS values it received from the UAC (after normalization with route PSPs).
The SBC relays the RTCP for pass-through and MRF transcoded calls. However, the SBC continues to terminate the RTCP for the SBC transcoded calls.
The following call flow scenarios provide RTCP behavior for the SBC pass-through calls, SBC transcoded calls, and MRF transcoded calls:
In these scenarios:
Scenarios | Call Flows | Pass-through Calls |
---|---|---|
1 | -------RR/RS=500-----> SBC----- RR/RS=500------> <-----RR/RS=400 ------ SBC <---- RR/RS=400 ------ | RCTP ports on the SBC: ON |
2 | -------RR/RS=500-----> SBC----- RR/RS=500------> <-----RR/RS=0 ------- SBC <---- RR/RS=0 ------ | RTCP ports on the SBC: OFF |
3 | -------RR/RS=500-----> SBC----- RR/RS=500------> <-----RR/RS=x ------- SBC <---- RR/RS=x ------ | RTCP ports on the SBC: ON |
4 | -------RR/RS=0-----> SBC------- RR/RS=0------> <-----RR/RS=0 -------SBC <---- RR/RS=0 ------ | RTCP ports on the SBC: OFF |
5 | -------RR/RS=0 -------> SBC------- RR/RS=0------> <-----RR/RS=400 -------SBC <---- RR/RS=400 ---- | RTCP ports on the SBC: OFF |
6 | -------RR/RS=0-----> SBC ----- RR/RS=0------> <-----RR/RS=x ------- SBC <---- RR/RS=x ------ | RTCP ports on the SBC: OFF |
7 | -------RR/RS=x -------> SBC ----- RR/RS=x------> <-----RR/RS=x ------- SBC <---- RR/RS=x ------ | RTCP ports on the SBC: ON |
8 | -------RR/RS=x -----> SBC----- RR/RS=x------> <-----RR/RS=0 -------SBC <---- RR/RS=0 ------ | RTCP ports on the SBC: OFF |
Scenarios | Call Flows | MRF Transcoded Calls |
---|---|---|
1 | -------RR/RS=500-----> SBC ----- RR/RS=500------> RR/RS sent by the SBC to the MRF: m1=500 | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: ON |
2 | -------RR/RS=500-----> SBC----- RR/RS=500------> <-----RR/RS=500 ----- SBC <---- RR/RS=0 ------ RR/RS sent by the SBC to the MRF: m1=500 | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: OFF |
3 | -------RR/RS=500-----> SBC----- RR/RS=500------> RR/RS sent by the SBC to the MRF: m1=500 | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: ON |
4 | -------RR/RS=0-----> SBC------- RR/RS=0------> RR/RS sent by the SBC to the MRF: m1=0 | Ingress RCTP port on the SBC: OFF Egress RCTP port on the SBC: OFF |
5 | -------RR/RS=0 -------> SBC------- RR/RS=0------> RR/RS sent by the SBC to the MRF: m1=0 | Ingress RCTP port on the SBC: OFF Egress RCTP port on the SBC: ON |
6 | -------RR/RS=0-----> SBC ----- RR/RS=0------> RR/RS sent by the SBC to the MRF: m1=0 | Ingress RCTP port on the SBC: OFF Egress RCTP port on the SBC: ON |
7 | -------RR/RS=x -------> SBC ----- RR/RS=x------> RR/RS sent by the SBC to the MRF: m1=x | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: ON |
8 | -------RR/RS=x -----> SBC----- RR/RS=x------> RR/RS sent by the SBC to the MRF: m1=x | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: OFF |
Scenarios | Call Flow | SBC Transcoded Call |
---|---|---|
1 | -------RR/RS=500-----> SBC ----- RR/RS=500------> <-----RR/RS=500 ------ SBC <---- RR/RS=400 ------ | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: ON |
2 | -------RR/RS=500-----> SBC----- RR/RS=500------> <-----RR/RS=500 ----- SBC <---- RR/RS=0 ------ | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: OFF |
3 | -------RR/RS=500-----> SBC----- RR/RS=500------> <-----RR/RS=500 ------ SBC <---- RR/RS=x ------ | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: ON |
4 | -------RR/RS=0-----> SBC------- RR/RS=0------> <-----RR/RS=0 -------SBC <---- RR/RS=0 ------ | Ingress RCTP port on the SBC: OFF Egress RCTP port on the SBC: OFF |
5 | -------RR/RS=0 -------> SBC------- RR/RS=0------> <-----RR/RS=0 -------SBC <---- RR/RS=400 ---- | Ingress RCTP port on the SBC: OFF Egress RCTP port on the SBC: OFF |
6 | -------RR/RS=0-----> SBC ----- RR/RS=0------> <-----RR/RS=0 ------- SBC <---- RR/RS=x ------ | Ingress RCTP port on the SBC: OFF Egress RCTP port on the SBC: OFF |
7 | -------RR/RS=x -------> SBC ----- RR/RS=x------> <-----RR/RS=x ------- SBC <---- RR/RS=x ------ | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: ON |
8 | -------RR/RS=x -----> SBC----- RR/RS=x------> <-----RR/RS=x -------SBC <---- RR/RS=0 ------ | Ingress RCTP port on the SBC: ON Egress RCTP port on the SBC: OFF |