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Content for  TS 23.228  Word version:  19.4.0

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AC.7.10 Multiplexing multiple DC streams over single SCTP connection  AC.7.10.1 General  AC.7.10.2 Capability negotiation  AC.7.10.2.1 Capability negotiation between UE and IMS network  AC.7.10.2.2 Capability negotiation between originating and terminating network  AC.7.10.3 Determination and handling of multiplexing and de-multiplexing  AC.7.10.3.1 Determination of multiplexing and de-multiplexing  AC.7.10.3.2 Handling multiplexing and de-multiplexing at the originating network  AC.7.10.3.3 Handling at the terminating network.  AC.7.10.4 Procedures  AC.7.10.4.1 Bootstrap data channel establishment 
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AC.7.10  Multiplexing multiple DC streams over single SCTP connection |R19|  p. 401

AC.7.10.1  General  p. 401

When multiple data channels are used in an IMS session, the UE and IMS network may support SDP negotiation to multiplex multiple data channel streams into a single data channel SDP media description m line and transport streams of multiple applications in the same SCTP connection, to save the number of m lines used by the UE and to improve the efficient usage of media resources.
The UE and IMS network also need to support data channel de-multiplexing when supporting data channel multiplexing. If the UE receives streams targeting to different applications over a single SCTP connection, it identifies the applications and delivers the data of the streams to corresponding applications. If the IMS network receives multiplexed streams which have different remote endpoints, e.g. a local bootstrap data channel and a remote bootstrap data channel of a UE, the MF terminates the multiplexing and sends different streams to corresponding endpoints based on instructions of DCSF.
The following multiplexing scenarios are supported in this Release:
  • Multiplexing local bootstrap data channel and remote bootstrap data channel between the UE and its home IMS network using a single SDP m line media description if both support data channel multiplexing capability;
  • Multiplexing different application data channels for applications with compatible QoS requirements between the UE and its IMS network using a single SDP m line media description if both support multiplexing capability;
  • Multiplexing different application data channels for applications with compatible QoS requirements between the originating IMS network and terminating IMS network using a single SDP m line media description if both support DC multiplexing capability.
Multiplexing the data channels using the same stream ID are not supported.
The following de-multiplexing scenarios are supported in this Release:
  • The supporting IMS network de-multiplexes local bootstrap data channel and remote bootstrap data channel from a SDP media description towards a UE that does not support multiplexing;
  • The supporting IMS network de-multiplexes application data channels from a SDP media description, if the data channels have different endpoints e.g. a P2P application and a P2A application or towards a UE that does not support multiplexing;
  • The supporting originating IMS network de-multiplex data channels towards remote network if the remote network or remote UE does not support DC multiplexing.
If the UE decides to use data channel multiplexing, when the UE generates SDP offer in INVITE or re-INVITE request, the DC stream IDs associated with the data channels to be multiplexed and the binding information combined with the data channels are included in the SDP offer for a single m line.
The IMS AS notifies the event of data channel multiplexing along with the data channel media information and binding information to the DCSF if data channel multiplexing is allowed for the subscriber.
The DCSF determines whether and how the data channels are multiplexed or de-multiplexed. When the DCSF determines that some data channels are allowed to be multiplexed, it instructs the IMS AS to multiplex the specific data channel streams to the same m line on the MF. The IMS AS further instructs MF to reserve a single media termination for the streams to be multiplexed.
If the DCSF determines that a data channel needs to be de-multiplexed from a SCTP connection, it instructs the IMS AS to de-multiplex the specific data channel stream on the MF. Based on the instruction of the DCSF, the IMS AS further indicates the MF to reserve separate media termination for the de-multiplexed stream in stead of using the same media termination with other multiplexed streams.
If the IMS AS is instructed by DCSF to use data channel multiplexing, when IMS AS generates SDP offer in INVITE or re-INVITE request to remote network or serving UE, the DC stream IDs associated with the data channels to be multiplexed and the binding information combined with the data channels are included in the SDP offer for a single m line.
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AC.7.10.2  Capability negotiation  p. 402

AC.7.10.2.1  Capability negotiation between UE and IMS network  p. 402
When the UE supports IMS data channel and the UE is allowed to use IMS data channel, the UE and IMS network may negotiate DC multiplexing capability as follows:
  • The UE and the IMS network mutually negotiate their capabilities of data channel multiplexing during registration procedure.
  • If the UE supports data channel multiplexing, when the UE registers on the IMS network, the UE shall include a media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing in the initial and any subsequent REGISTER request.
  • If the home IMS network, including the P-CSCF, the IMS-AGW, the MF, supports data channel multiplexing, the S-CSCF includes a Feature-Caps header field indicating its capability of supporting data channel multiplexing in the 200 OK response to the initial and any subsequent REGISTER request.
  • If the IMS network supports this feature, the S-CSCF includes a Feature-Caps header field indicating its capability of supporting data channel multiplexing in the SIP request messages to the remote network.
  • If the UE supports and is allowed to use data channel multiplexing, the UE shall include the media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing in the initial INVITE or any re-INVITE request message, regardless of data channels being multiplexed or not.
  • If the S-CSCF has not included the data channel multiplexing capability indication in the Feature-Caps header field in the 200 OK response either to the initial REGISTER or a subsequent REGISTER request message, the UE shall not include the media feature tag indicating its capability of supporting data channel multiplexing in the Contact header field of the initial INVITE request or any subsequent re-INVITE request message.
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AC.7.10.2.2  Capability negotiation between originating and terminating network  p. 403
The DCSF in originating IMS network shall determine whether the terminating IMS network supports data channel multiplexing by local configuration or based on the SDP answer received from remote network setting port of multiplexed DC media to zero.
If the DCSF in originating IMS network receives session establishment failure 488 response to INVITE request from IMS AS and if the IMS session is a standalone IMS DC session, based on operator policy, the DCSF may assume the session failure is due to terminating network not supporting data channel multiplexing and instruct the IMS AS to de-multiplex all data channel media and resend INVITE request with de-multiplexed SDP offer as described in clause AC.7.10.3.1.
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AC.7.10.3  Determination and handling of multiplexing and de-multiplexing  p. 403

AC.7.10.3.1  Determination of multiplexing and de-multiplexing  p. 403
When the IMS AS receives the INVITE request with data channel multiplexing, if data channel multiplexing is supported, it reports the event to the DCSF for data channel management. The DCSF determines whether the data channel multiplexing is allowed and whether serving network needs to de-multiplex the data channel traffic based on subscription data, binding information, the endpoints of data channels and capability of terminating network.
When the IMS AS receives a response that rejects the multiplexed data channel media, e.g. a 18X with SDP answer setting port of multiplexed data channel media to zero, or a 488 response to the INVITE request of a standalone IMS DC session with multiplexed SDP offer, the IMS AS shall firstly report the session establishment failure event to the DCSF and follows the instructions from DCSF. The DCSF determines whether to release the session or retry the session establishment with normal SDP offer as specified in clause AC.7.10.2.2. If the DCSF determines to retry the session establishment, it instructs the IMS AS to modify the media resource of multiplexed data channels in the MF and further re-send INVITE request with de-multiplexing SDP offer after the media resource modification is successful.
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AC.7.10.3.2  Handling multiplexing and de-multiplexing at the originating network  p. 404
The IMS AS and DCSF in the originating network follows the following principles to handle data channel multiplexing and de-multiplexing:
  • If the data channels are kept multiplexed, the DCSF instructs originating IMS AS accordingly. The originating IMS AS further instructs the MF to reserve the same media termination for multiplexed data channels. This attempt may succeed and IMS session establishment may be successful.
  • If the data channels are kept multiplexed, the DCSF instructs originating IMS AS accordingly. The originating IMS AS further instructs the MF to reserve the same media termination for multiplexed data channels. If the terminating network rejects the SDP offer because the terminating network does not support multiplexing, then originating IMS AS and originating DCSF needs to revert to a new demultiplexed SDP offer towards the target network as described in next bullet.
  • If the originating network determines to de-multiplex the data channels, the DCSF in the originating network instructs originating IMS AS accordingly. The originating IMS AS further instructs the MF to reserve separate media terminations for the de-multiplexed streams. When the originating IMS AS sends the SDP offer to terminating IMS network, the data channels are not multiplexed in the SDP offer. IMS session establishment continues.
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AC.7.10.3.3  Handling at the terminating network.  p. 404
The IMS AS and DCSF in the terminating network follows the following principles to handle data channel multiplexing and de-multiplexing:
  • If the data channels are kept multiplexed, the terminating DCSF instructs terminating IMS AS accordingly. The terminating IMS AS further instructs the MF to reserve the same media termination for multiplexed data channels;
  • If the data channels is determined to be de-multiplexed, the terminating DCSF instructs terminating IMS AS accordingly. The terminating IMS AS further instructs the MF to reserve separate media terminations for the de-multiplexed streams. When the terminating IMS AS sends the SDP offer to terminating UE, the data channels are not multiplexed in the SDP offer.
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AC.7.10.4  Procedures  p. 404

AC.7.10.4.1  Bootstrap data channel establishment  p. 404
AC.7.10.4.1.1  Bootstrap data channels multiplexing in originating network  p. 404
Figure AC.7.10.4.1.1-1 shows the procedure when the local bootstrap data channel and remote bootstrap data channel is multiplexed by the originating UE. The originating UE initiates an IMS session with multiplexed SDP for the two bootstrap data channels. The originating IMS network de-multiplexes the bootstrap data channel due to the two data channels have different endpoints.
Reproduction of 3GPP TS 23.228, Fig. AC.7.10.4.1.1-1: Multiplexing bootstrap data channels in originating network
Figure AC.7.10.4.1.1-1: Multiplexing bootstrap data channels in originating network
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Step 1.
When the UE wants to multiplex its bootstrap data channels, i.e. local bootstrap data channel and remote bootstrap data channel, the UE includes multiplexed SDP media description in initial INVITE request. The media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing is included in reINVITE request.
Step 2-3.
The IMS AS selects and report event to DCSF.
Step 4.
The DCSF determines based on stream id in the SDP that local bootstrap and remote bootstrap data channels need to be de-multiplexed.
Step 5.
The DCSF generates data channel media information for originating side and terminating side.
Step 6.
The DCSF instructs the IMS AS to reserve resources on MF.
Step 7.
The IMS AS selects MF supporting data channel multiplexing.
Step 8.
The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF.
Step 9-12.
The session continues after the media resource is reserved successfully. The SDP offer in the INVITE request may also be multiplexed if needed.
Step 13-16.
The terminating network responds and the session is established successfully.
The streams of local data channel and remote data channel are transported in the same SCTP connection between UE#1 and MF and are routed to DCSF and remote network correspondingly.
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AC.7.10.4.1.2  Bootstrap data channel multiplexing in terminating network  p. 406
Figure AC.7.10.4.1.2-1 shows the procedure when the terminating IMS network multiplexes the received remote data channel and the local bootstrap data channel towards the terminating UE.
In this procedure, when the terminating IMS network receives the SDP offer of remote bootstrap DC for terminating UE, it multiplexes this bootstrap data channel with the local bootstrap data channel for terminating UE. When the terminating UE receives the multiplexed SDP offer, it replies with the multiplexed SDP answer to allow multiplexing of the two bootstrap data channels between terminating UE and terminating IMS network.
Reproduction of 3GPP TS 23.228, Fig. AC.7.10.4.1.2-1: Multiplexing bootstrap data channels in terminating network
Figure AC.7.10.4.1.2-1: Multiplexing bootstrap data channels in terminating network
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Step 1.
The originating network sends initial INVITE request with SDP offer for remote bootstrap data channel to UE#2.
Step 2-3.
The IMS AS selects and reports event to DCSF.
Step 4.
The DCSF determines that local bootstrap and remote bootstrap data channels to UE#2 need to be multiplexed.
Step 5.
The DCSF generates data channel media information for originating side and terminating side.
Step 6.
The DCSF instructs the IMS AS to reserve resources on MF.
Step 7.
The IMS AS selects MF supporting data channel multiplexing.
Step 8.
The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF.
Step 9-12.
The session continues after the media resource is reserved successfully.
Step 13-16.
The UE#2 responds and the session is established successfully.
The streams of local data channel and remote data channel are transported in the same SCTP connection to UE#2.
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