Content for TS 24.186 Word version: 19.4.0

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9.3.3.2 Procedures at the serving IMS AS for the terminating UE 9.3.3.2.1 IMS bootstrap data channel establishment in conjunction with MMTel session setup 9.3.3.2.2 MMTel session modification 9.3.3.2.3 MMTel session release 9.3.3.2.4 Support of IMS standalone data channel session 9.3.3.2.5 Enforcement of 3GPP PS data off 9.3.3.2.6 Handling of data channel multiplexing 9.3.3.2.7 Support of data channel interworking between a non-DC capable originating UE and a DC capable terminating UE
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9.3.3.2 Procedures at the serving IMS AS for the terminating UE p. 36

9.3.3.2.1 IMS bootstrap data channel establishment in conjunction with MMTel session setup p. 36

Upon receipt of a SIP initial INVITE request with the SDP offer including IMS data channel media descriptions from the originating network, if the IMS AS determined that the terminating registered UE:

supports IMS data channel capabilities and is authorized to use IMS data channel, the IMS AS shall notify the DCSF about a session establishment request event, with a calling identity set to the value of the P-Asserted-Identity header field and a called identity set to the value of Request URI of the received initial INVITE request, and shall not send a INVITE request to the S-CSCF until receiving an acknowledgement from the DCSF. Based on the received Media instruction set from the DCSF, the IMS AS shall select the MF and request the MF to allocate required data channel media resources. Based on the response of the reserved media resource from the MF, the IMS AS shall:
- delete the remote bootstrap data channel media description for the originating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110 and "a=3gpp-bdc-used-by" attribute with "bdc-used-by" parameter set to value "sender"), i.e. the remote bootstrap data channel between originating UE and terminating network in the SDP offer;
- replace the IP address represented in the "c=" line, the UDP port number in the "m=application" line as well as the DC endpoint information represented as the attribute lines including the "a=tlsId", "a=sctp-port", "a=fingerprint" and "a=setup" line in the remote bootstrap data channel media description for the terminating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110 and "a=3gpp-bdc-used-by" attribute with "bdc-used-by" parameter set to value "receiver"), i.e. the remote bootstrap data channel between terminating UE and originating network, with the media resource information for the termination towards the terminating UE if the media in anchored on the MF; and
  - generate and add the local bootstrap data channel media description for the terminating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0 and 10), i.e. the local bootstrap data channel between the terminating network and terminating UE to the SDP offer.
upon the reception of a successful acknowledgement from the DCSF to the session establishment request event notification, the IMS AS shall send the initial INVITE request with the modified SDP offer via the S-CSCF towards the terminating registered UE of the served user, which support the IMS data channel capabilities; or
does not support IMS data channel capabilities or is not authorized to use IMS data channel, then based on the operator policy the IMS AS shall determine whether to remove from the SDP offer media lines related to the IMS data channels:
1. if the operator policy indicates removal of media lines related to the IMS data channels, the IMS AS shall not trigger the DC media resource reservation and the IMS AS shall remove from the received SDP offer media lines describing the bootstrap data channel(s) i.e.:
  - "dcmap" attribute lines containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0, 10, 100 and 110; and
  - if present, "a=3gpp-bdc-used-by:" attribute lines,
  associated with the "m=" line containing the media set to "application", the UDP port number, the proto value set to "UDP/DTLS/SCTP" and the fmt value set to "webrtc-datachannel". If there are no other "dcmap" attribute lines that contain a subprotocol parameter set to value other than "http", the IMS AS shall remove any other SDP media attribute lines associated with that m line e.g., "sctp-port", "max-message-size", "tls-id", "a=setup", "a=3gpp-qos-hint" SDP attribute lines. The IMS AS shall send the SIP initial INVITE request with the modified SDP offer to the S-CSCF towards the terminating registered UE of the served user.

Upon receipt of a SIP initial INVITE request with the SDP offer not including IMS data channel media descriptions from the originating network, if the IMS AS determined that the terminating registered UE supports IMS data channel capabilities and is authorized to use IMS data channel, the IMS AS shall notify the DCSF of a session establishment request event and shall not send a INVITE request to the S-CSCF until receiving an acknowledgement from the DCSF. Based on the received media instruction set from the DCSF, the IMS AS shall select an MF and request the MF to allocate required data channel media resources.

Based on the response of the reserved media resource from the MF, the IMS AS shall generate and add the local bootstrap data channel media description for the terminating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0 and 10), i.e. the local bootstrap data channel between the terminating network and terminating UE to the SDP offer. Upon the reception of a successful acknowledgement from the DCSF to the session establishment request event notification, the IMS AS shall send the initial INVITE request with the modified SDP offer via the S-CSCF towards the terminating registered UE of the served user, which support the IMS data channel capabilities. If no media instruction received from the DCSF or no acknowledgement from the DCSF received, the IMS AS shall forward the initial INVITE request from the originating network (i.e. without IMS data channel media descriptions in the SDP offer) to the S-CSCF.

Upon receipt of the 18x or 2xx response on the initial INVITE message including the SDP answer which includes the data channel media description, the IMS AS shall notify the DCSF about corresponding session event (session establishment progress (i.e. receiving the 183 (Session Progress) response ), session establishment alerting (i.e. receiving the 180 (Ringing) response) or session establishment success (i.e. receiving the 200 (OK) response on the INVITE request) event) and shall request the MF to update the media resources. Based on the response from the MF, the IMS AS shall:

generate and add the remote bootstrap data channel media description for the originating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110 and "a=3gpp-bdc-used-by" attribute with "bdc-used-by" parameter set to value "sender") in the SDP answer, i.e. the remote bootstrap data channel between originating UE and terminating network;
replace the IP address represented in the "c=" line, the UDP port number in the "m=application" line as well as the DC endpoint information represented as the attribute lines "a=tlsId", "a=sctp-port", "a=fingerprint" and "a=setup" line within the remote bootstrap data channel media description for the terminating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110 and "a=3gpp-bdc-used-by" attribute with "bdc-used-by" parameter set to value "receiver"), i.e. the remote data channel between terminating UE and originating network, with the DC endpoint information for the termination towards the originating network allocated by the MF; and
delete the bootstrap data channel media description (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0 and 10) in the SDP answer, i.e. the bootstrap data channel between terminating UE and terminating network.

Upon receipt of the 18x or 2xx response including the SDP answer which only contains the data channel media description for the bootstrap data channel between terminating UE and terminating network, the IMS AS shall notify the DCSF, request the MF to update the media resources as above and delete this bootstrap data channel media description (i.e. the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0 and 10) in the SDP answer.

Upon the reception of an acknowledgement from the DCSF to the corresponding notification, the IMS AS shall include the modified SDP answer for data channel to originating network and send the 18x or 2xx response on the initial INVITE request to the S-CSCF.

Upon receipt of a CANCEL request the initial INVITE request, the IMS AS shall notify the DCSF about the session establishment cancellation, request the MF to release the corresponding data channel media resources, and forward the CANCEL request to the S-CSCF towards the terminating UE.

Upon receipt of a 4xx, 5xx or 6xx response on the initial INVITE request from the terminating UE, the IMS AS shall notify the DCSF about session establishment failure, and request MF to release the data channel media resources.

9.3.3.2.2 MMTel session modification p. 38

9.3.3.2.2.1 IMS bootstrap data channel establishment p. 38

If the IMS AS received from the originating network a re-INVITE request with the SDP offer containing data channel media description for the bootstrap data channel establishment, if the IMS AS determined that the terminating registered UE:

supports IMS data channel capabilities and is authorized to use IMS data channel, the IMS AS shall notify the DCSF about the media change request, with a calling identity set to the value of the P-Asserted-Identity header field and a called identity set to the value of Request URI of the initial INVITE request received during MMTel session establishment. If the media instruction from the DCSF is:
does not support IMS data channel capabilities or is not authorized to use IMS data channel, the procedure defined in clause 9.3.3.2.1 applies.

If the IMS AS received from the served user a re-INVITE request with the SDP offer containing data channel media description for the bootstrap data channel establishment, the procedure of the IMS AS in the originating network on receipt of a re-INVITE request from the originating UE defined in clause 9.3.2.2.2.1 applies.

9.3.3.2.2.2 IMS application data channel establishment p. 39

Upon receipt of a re-INVITE request with the SDP offer including new application data channel media descriptions (the media lines with the "dcmap" attribute containing "stream-id" parameter set to values starting at 1000) along with the video, audio, and bootstrap data channel media descriptions from the originating network, the IMS AS shall notify the DCSF about the media change request. If the media instruction from the DCSF is

to reject all the data channel medias in this request, the IMS AS shall send a 488 (Not Acceptable Here) response to the originating network and other medias are not updated; and
in other cases, the IMS AS shall request MF to update the media resources. Based on the response on the data channel media resource update from the MF as specified in TS 29.176 and media instruction from DCSF as specified in TS 29.175, the IMS AS shall:
1. delete the data channel media description (media line with the "dcmap" attribute containing "stream-id" parameter set to the values starting at 1000 and "a=3gpp-req-app " attribute with "endpoint" parameter set to value "server") if the media instruction from DCSF is to terminate the media;
2. delete the data channel media description if the media instruction from DCSF is to reject the media as specified in TS 29.175 and there are other medias to be established;
3. replace the IP address represented in the "c=" line, the UDP port number in the "m=application" line in the data channel media description in the SDP offer with the media resource information for the termination towards the terminating UE allocated by the MF if the media instruction from DCSF is to terminate and originate the media, and also replace the DC endpoint information represented as the attribute lines "a=tlsId", "a=sctp-port", "a=fingerprint" and "a=setup" when the media proxy configuration is HTTP proxy; and
4. generate and add a data channel media description (media line with the "dcmap" attribute containing "stream-id" parameter set to values starting at 1000 and "a=3gpp-req-app " attribute with "endpoint" parameter set to value "server") by using the DC stream information provided by the DCSF in the attribute lines "a=dcmap" and "a=3gpp-req-app", DC endpoint information of the DC AS provided by the DCSF in the attribute lines "a=tlsId", "a=sctp-port", "a=fingerprint" and "a=setup", IP address and UDP port number allocated on the termination towards to the terminating UE on the MF in the "c=" line and "m=application" when the media proxy configuration is UDP proxy, or using the DC stream information provided by the DCSF in the attribute lines "a=dcmap" and "a=3gpp-req-app" and the IP address, UDP port number and DC endpoint information (e.g. tlsId, sctp-port) allocated on the termination towards to the terminating UE on the MF in the other attribute lines above when the media proxy configuration is HTTP proxy, if the media instruction from DCSF is to originate a new media as specified in TS 29.175.
an existing application data channel media description in which the new "a=dcmap" line containing the "stream-id" parameter value set to values starting at 1000 is added, the IMS AS shall notify the DCSF about media change request, and request MF to update the media resource if the media instruction from DCSF is to update the media.
The IMS AS shall send the re-INVITE request to the S-CSCF with the modified SDP offer including the modified application data channel media description or the original application data channel media description if no media instruction received from DCSF as well as the media descriptions of established video, audio and bootstrap data channels, to the terminating UE.

Upon receipt of the 183 (Session Progress) or 200 (OK) response on the re-INVITE request with the SDP answer which contains media description of the requested application data channel from the terminating UE,

if the application data channel is accepted, the IMS AS shall notify DCSF about the media change success and request the MF to update the media resources. Based on the response of the MF, the IMS AS shall:
1. generate and add a data channel media description in the SDP answer by using DC endpoint information of the DC AS provided by the DCSF in the attribute lines "a=tlsId", "a=sctp-port", "a=fingerprint" and "a=setup" and the IP address and the UDP port number allocated on the termination towards to the originating network on MF in the lines "c=" and "m=application", or using the IP address, the UDP port number and the DC endpoint information (e.g. tlsId, sctp-port) allocated on the termination towards to the originating network on the MF in the attribute lines above when the media proxy configuration is HTTP proxy, if the instruction from the DCSF is to terminate the media;
2. add the rejected media description and set the port number to 0 in the "m=application" line if the instruction from the DCSF is to reject the media and there are other medias to be established;
3. replace the IP address represented in the "c=" line, the UDP port number in the "m=application" line in the media description in the SDP answer with the media resource information on the termination towards to the originating network allocated by the MF if the instruction from the DCSF is to terminate and originate the media and also replace the DC endpoint information as attribute lines "a=tlsId", "a=sctp-port", "a=fingerprint" and "a=setup" when the media proxy configuration is HTTP proxy; and
4. delete the media description in the SDP answer if the instruction from the DCSF is to originate a new media;
and send the 183 (Session Progress) or 200 (OK) response with the modified SDP answer on the re-INVITE request to the S-CSCF towards to the originating network after the receipt of an acknowledgement from the DCSF to the corresponding notification; or
if the application data channel is rejected, the IMS AS shall notify the DCSF about media change failure and request the MF to release the media resources. The IMS AS shall send the 183 (Session Progress) or 200 (OK) response to S-CSCF with the modified SDP answer for the requested application data channel as well as the media descriptions of established video, audio, and bootstrap data channels after the receipt of an acknowledgement from the DCSF to the corresponding notification.

Upon receipt of a CANCEL request to the re-INVITE request, the IMS AS shall notify the DCSF about the media change cancellation, request the MF to release the corresponding data channel media resources and forward the CANCEL request to the S-CSCF towards the terminating UE.

Upon receipt of a 4xx, 5xx or 6xx response on the re-INVITE request from the terminating UE, the IMS AS shall notify the DCSF about media change failure, request the MF to release the corresponding data channel media resources and forward the response to the originating network.

Upon receiving the re-INVITE request from the terminating UE to setup an application data channels and the corresponding response form the originating network, the procedure in clause 9.3.2.2.2.2 applies.

9.3.3.2.2.3 Closing application data channel p. 40

Upon receipt of the re-INVITE request with an SDP offer which contains an existing application data channel media description in which the UDP port number is set to 0, the IMS AS shall notify the DCSF about media change request, and request the MF to release the corresponding media resource if the media instruction from DCSF is to delete the media.

Upon receipt of the re-INVITE request with an SDP offer which contains an existing application data channel media description in which an existing "a=dcmap" line is removed, the IMS AS shall notify the DCSF about media change request, and request MF to update the media resource if the media instruction from DCSF is to update the media.

Upon receipt of the 200 (OK) response on the re-INVITE message with the SDP answer, the procedure in clause 9.3.3.2.2.2 applies.

Upon receiving the re-INVITE request from the terminating UE to close an application data channels and the corresponding 200 (OK) response form the originating network, the procedure in clause 9.3.2.2.2.3 applies.

9.3.3.2.2.4 Network-determined closing of bootstrap and application data channel p. 40

If the IMS AS determines to terminate the established bootstrap data channels and application data channels to the originating UE during the session modification (e.g. due to supplementary service procedures as specified in clause 10.19.2), the IMS AS shall send a re-INVITE request to the originating network with the subsequent SDP offer and set the UDP port number of the data channel media descriptions to zero.

9.3.3.2.3 MMTel session release p. 40

Upon initiation or receipt of a BYE request matching an existing MMTel session with IMS data channel, the procedure defined in clause 9.3.2.2.3 applies.

9.3.3.2.4 Support of IMS standalone data channel session |R19| p. 41

9.3.3.2.4.0 General p. 41

If the IMS AS received from the originating network:

an initial INVITE request with the SDP offer containing only data channel media description;
a re-INVITE request with the SDP offer in which the audio and video media is removed (i.e. the port number of the audio/video media set to 0);

the IMS AS shall determine whether the served user is authorized to use a standalone IMS data channel or not by the local configuration or the subscription data. If the user is not authorized to use IMS standalone data channel, the IMS AS shall send 403 (Forbidden) to the originating network to reject the session or to reject the media change request.

If the IMS AS received from the terminating UE:

an initial INVITE request with the SDP offer containing only data channel media description;
a re-INVITE request with the SDP offer in which the audio and video media is removed (i.e. the port number of the audio/video media set to 0);

the requirements in clause 9.3.2.2.4.1 applies.

9.3.3.2.4.1 Void

9.3.3.2.4.1A Subsequent standalone bootstrap data channel and application data channel establishment p. 41

Upon receipt of the initial INVITE request from the originating network towards a terminating UE with the SDP offer which only includes bootstrap data channels and the 183 (Session Process) response to the INVITE request with the SDP answer, from the terminating UE, the IMS AS shall follow the procedure in clause 9.3.3.2.1 to handle the bootstrap data channel media.

Upon receipt of the UPDATE request from the originating network with an updated SDP offer that contains a data channel media description for the established bootstrap data channel, as well as the requested application data channel and the associated DC application binding information (provided within the "a=3gpp-req-app" SDP attribute) and the 200 (OK) response to the UPDATE request from the terminating UE, the IMS AS shall follow the procedures upon receipt of the re-INVITE request and the response to the re-INVITE request in clause 9.3.2.2.2.2 to handle the application data channel media.

Upon receipt of the 200 (OK) response to the initial INVITE request from the terminating UE, the IMS AS shall notify the DCSF about the session establishment success event and forward the 200 (OK) response to the originating network.

9.3.3.2.4.2 Void

9.3.3.2.4.3 Combined standalone bootstrap data channel and application data channel establishment p. 41

Upon receipt of the initial INVITE request from the originating network to a terminating UE with SDP offer which includes the media description for both bootstrap data channel and application data channel and the 183 (Session Process) response to the initial INVITE request from the terminating UE, the IMS AS shall follow the procedure in clause 9.3.3.2.1 to handle the bootstrap data channel media and clause 9.3.2.2.2.2 to handle the and application data channel media.

Upon receipt of the UPDATE request from the originating network with an updated SDP offer that contains a data channel media description for the established bootstrap data channel, as well as the requested application data channel and the associated DC application binding information (provided within the "a=3gpp-req-app" SDP attribute) and the 200 (OK) response to the UPDATE request from the terminating UE, the IMS AS shall follow the procedure in clause 9.3.3.2.2.2 to handle the application data channel media.

9.3.3.2.5 Enforcement of 3GPP PS data off |R19| p. 42

If "Services over IMS Data Channel" is not in the list of 3GPP PS data off exempt services, upon receipt of a third-party REGISTER request containing a "+g.3gpp.ps-data-off" Contact header field parameter indicating the 3GPP PS data off status of the UE, in addition to the procedure in clause 5.7.1.26 of TS 24.229, the IMS AS serving the UE:

may notify the DCSF about the 3GPP PS data off status of the UE by session establishment request event and PS data off status change event as specified in TS 29.175, and clause X.3.2 of TS 23.228;
if the 3GPP PS data off status of the UE is changed from "inactive" to "active":
- when a re-INVITE request to the served UE is received, if the SDP offer from the re-INVITE request contains only the data channel media descriptions, the IMS AS shall:
  1. send a 403 response to the originating side;
  2. send BYE request towards the originating and terminating side;
  3. shall notify the DCSF about a session termination event due to the activation of the 3GPP PS data off and "Services over IMS Data Channel" is not in the list of 3GPP PS data off exempt services; and
  4. if the MF already allocated IMS data channel media resources, shall request the MF to release the allocated data channel media resource; or
- when an SDP offer from the received re-INVITE request contains other media description(s) in addition to data channel media descriptions, shall remove the data channel media descriptions from the received SDP offer before sending re-INVITE request to the served UE, and set the port number of the "m=" lines for the data channel media description as zero in the SDP answer of the response to the corresponding re-INVITE request towards the originating side.

9.3.3.2.6 Handling of data channel multiplexing |R19| p. 42

9.3.3.2.6.1 General p. 42

When the IMS AS receives from the originating network an initial INVITE with the SDP offer containing only the multiplexed data channel media description(s), if the data channel multiplexing is not supported by the terminating network, the IMS AS shall return 488 (Not Acceptable Here) response containing an SDP message body.

9.3.3.2.6.2 Bootstrap data channel multiplexing p. 42

When the IMS AS receives from the originating network an initial INVITE, a re-INVITE or an UPDATE request with an SDP offer that contains a multiplexed bootstrap media description from the originating network, if the data channel multiplexing is supported by the terminating network and the served UE, the IMS AS shall select and notify the DCSF as specified in clause 9.3.3.2.1, clause 9.3.3.2.2, and clause 9.3.3.2.4.

Based on the instruction of the DCSF, the IMS AS shall select an MF supporting data channel multiplexing and request the MF to allocate data channel media resources for the multiplexed data channels. Based on the response from the MF, the IMS AS shall modify the SDP offer:

delete the media description which contains the remote bootstrap data channel in which the "dcmap" attribute line containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110 and the "a=3gpp-bdc-used-by:" attribute line containing "bdc-used-by" parameter set to value "sender", if the media instruction from the DCSF is to delete the media;
generate a multiplexed bootstrap data channel media description by adding the local bootstrap data channel related attributes for the terminating UE (i.e. the bootstrap data channel between the terminating network and terminating UE related attributes (the "dcmap" attribute line containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0 and 10) in the media description which contains the remote bootstrap data channel for the terminating UE (the "dcmap" attribute line containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110), if the DCSF indicates the media is to be multiplexed and the media instruction from the DCSF is to terminate and originate the media;

Upon the reception of an acknowledgement from the DCSF to the event notification, the IMS AS shall send the received SIP request with the modified SDP offer towards the terminating UE.Upon receipt of the 18x or 2xx response including SDP answer to the initial INVITE, re-INVITE or UPDATE request from the served UE, the IMS AS shall notify the DCSF about corresponding session event or media change event and request the MF to update the media resource as specified in clause 9.3.3.2.1, clause 9.3.3.2.2, and clause 9.3.3.2.4. Based on the response from the MF, the IMS AS shall modify the SDP answer:

generate and add the remote bootstrap data channel media description for the originating UE (the media line with the "dcmap" attribute containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110 and "a=3gpp-bdc-used-by" attribute with "bdc-used-by" parameter set to value "sender") in the SDP answer, i.e. the remote bootstrap data channel between originating UE and terminating network;
delete the local bootstrap data channel related attributes for the terminating UE (i.e. the bootstrap data channel between the terminating network and terminating UE related attributes (the "dcmap" attribute line containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 0 and 10) in the received multiplexed bootstrap data channel media description which contains the remote bootstrap data channel for the terminating UE (the "dcmap" attribute line containing a subprotocol parameter set to "http" and "stream-id" parameter set to values 100 and 110), and replace the IP address as well as the DC endpoint information with the media resource information allocated by the MF towards the originating network;

and send the response with the modified SDP answer towards to the originating network.

When the IMS AS receives from the originating network an initial INVITE, a re-INVITE or an UPDATE request with an SDP offer that contains a multiplexed bootstrap media description from the originating network, if the data channel multiplexing is not supported by the served UE, the IMS AS shall follow the procedures as specified in clause 9.3.3.2.1, clause 9.3.3.2.2, and clause 9.3.3.2.4.

9.3.3.2.6.3 Application data channel multiplexing p. 43

When the IMS AS receives from the originating network an initial INVITE, re-INVITE or UPDATE request with an SDP offer that contains a multiplexed application data channel media description, if the data channel multiplexing is supported and it determines the terminating UE:

supports the data channel multiplexing, the procedure in clause 9.3.3.2.2 applies; or
does not support the data channel multiplexing, the IMS AS shall de-multiplex the application data channel media based on the instruction of DCSF, i.e.
1. generate and add new media descriptions for the de-multiplexed data channel not using the same media Id as the original multiplexed media in the SDP offer, and
2. remove the "a=dcmap" lines and the related "a=3gpp-req-app" lines that are described in separate media descriptions as specified in bullet 1) in the original multiplexed media description,
  and send the re-INVITE with the de-mulitplexed application data channel media description to the terminating UE.

Upon receipt of the 18x or 200 (OK) response from the terminating UE to the INVITE, re-INVITE or UPDATE request with demultiplexed data channel media description in SDP answer, the IMS AS shall multiplex the data channel media descriptions in the SDP answer using the original multiplexed media id in the SDP offer and send the 18x or 200 (OK) response to the originating network.

9.3.3.2.7 Support of data channel interworking between a non-DC capable originating UE and a DC capable terminating UE |R19| p. 43

Upon receipt of an initial INVITE request with an SDP offer containing the audio and video media description from the originating network, if the interworking required event subscribed and the IMS AS determines that the originating UE is a non-DC capable UE as the Contact header field does not include the media feature tag defined in RFC 5688 for supported streaming media type with +sip.app-subtype="webrtc-datachannel" as specified in TS 26.114, the IMS AS shall notify the NEF or the trusted AF about the interworking required event based on the subscription from them as specified in clause AC.7.9.4 of TS 23.228 and TS 29.175.

After the final response of the initial INVITE request received, the IMS AS shall notify the NEF or the trusted AF about IMS session establishment event based on the subscription as specified in clause AC.7.9.4 of TS 23.228 and TS 29.175.