8 Roles for call modifcation initiated from the ICS UE
24.2923GPPIP Multimedia (IM) Core Network (CN) subsystem Centralized Services (ICS)Release 17Stage 3TS
8.1 Introduction
This clause specifies call modification procedures initiated by an ICS UE for a call using a service control signalling path over Gm. The associated procedures for the ICS UE and the SCC AS are also specified in this clause; specifically, the procedure when a CS bearer is added or removed is specified. If a CS bearer is already used for the session, the ICS UE can add or remove video media to/from the existing CS bearer by applying the procedures in accordance with 3GPP TS 24.229 [11] and the CS SDP as described in IETF RFC 7195 [36].
8.2 ICS UE
8.2.1 General
This clause specifies the procedures for a UE when the call modification is initiated by an ICS UE.
8.2.2 ICS UE is using Gm
8.2.2.1 General
This subclause specifies call modification procedure when a session is modified from an ICS UE using a service control signalling path over Gm; specifically, the procedure when a CS bearer is added or removed is specified.
8.2.2.2 ICS UE adds a CS bearer
If the UE decides to add a CS bearer to an existing session, the ICS UE shall act in accordance with subclause 7.2.2, except that a SIP re-INVITE request and its related responses shall be used instead of an initial SIP INVITE request.
8.2.2.3 ICS UE adds media in PS domain
If the ICS UE decides to add a media using the PS domain, the ICS UE shall apply the procedure in accordance with 3GPP TS 24.229 [11].
8.2.2.5 ICS UE removes a CS bearer
When an ICS UE wants to remove a CS bearer the ICS UE shall:
a) send a SIP re-INVITE request or SIP UPDATE request towards the IM CN subsystems as specified in 3GPP TS 24.229 [11]. The ICS UE shall populate the SIP INVITE request or SIP UPDATE request as follows:
i) the request URI set to the contact address earlier received from the SCC AS;
ii) include in the Contact header field:
– a public GRUU or temporary GRUU as specified in 3GPP TS 24.229 [11] if a GRUU was received at registration;
– the g.3gpp.ics media feature tag set to "principal";
b) set the CS bearer to not be used any longer by setting the port number to zero for the CS media "m=" line with the proto portion set to "PSTN" as described in IETF RFC 7195 [36]; and
c) when the ICS UE receives a reliable 1xx provisional response from the IM CN subsystem, the ICS UE shall release the resources in accordance with 3GPP TS 24.008 [8].
8.2.2.6 ICS UE removes PS media
If the ICS UE decides to remove any media using the PS domain the ICS UE shall apply the procedure in accordance with 3GPP TS 24.229 [11].
8.2.2.7 ICS UE add/remove CS video media
In case that a CS bearer is already used for the session and that the ICS UE decides to add or remove CS video media to/from the existing CS bearer, the ICS UE shall apply the procedures in accordance with 3GPP TS 24.229 [11] and the CS SDP as described in IETF RFC 7195 [36].
In the CS domain, the ICS UE shall apply in-call modification procedure (i.e., speech to/from UDI/RDI multimedia mode) as specified in 3GPP TS 24.008 [8] if it is possible, otherwise, the ICS UE shall apply Redial method as specified in 3GPP TS 24.008 [8].
8.3 MSC server enhanced for ICS
No special procedure is required for call modification procedure at the MSC Server enhanced for ICS.
8.4 SCC AS
8.4.1 General
This subclause specifies call modification procedure when a session is modified from an SCC AS using a service control signalling path over Gm; specifically, the procedure when a CS bearer is added or removed is specified.
8.4.2 SCC AS actions when UE adds a CS bearer
When the SCC AS receives a SIP re-INVITE request from the ICS UE indicating the addition of a CS bearer on an existing session, the SCC AS shall:
1) if the SDP offer in the received SIP INVITE request contains:
i) a "c=" line with nettype portion set to "PSTN" as described in IETF RFC 7195 [36];
ii) a CS media "m=" line with media portion set to audio, port portion set to "9" and nettype portion set to "PSTN" as described in IETF RFC 7195 [36];
NOTE: If both i) and ii) are true, the ICS UE is requesting that the media bearer is to be set up over the CS domain.
iii) an a=cs-correlation attribute set to "callerid" along with the MSISDN, of the ICS UE in the CS domain, in international E.164 number format; and
iv) an a=setup attribute set to "active" and an a=connection attribute set to "new"
then the SCC AS shall send a SIP 183 (Session Progress) response towards the originating ICS UE in accordance with 3GPP TS 24.229 [11] with the following additions:
a) include an SDP answer, in accordance with IETF RFC 7195 [36], containing a "c=" line with the nettype portion set to "PSTN" and with the addrtype portion set to "E164" and the connection-address portion set to a SCC AS PSI DN, in international E.164 number format. The SCC AS PSI DN is associated with the SCC AS and identifies the existing session;
b) an a=setup attribute set to "passive";
c) an a=connection attribute set to "new";
d) an a=cs-correlation attribute set to "callerid;
e) indicate local preconditions not met for the media over CS bearer; and
2) When the SCC AS receives an initial SIP INVITE with the Request-URI containing a valid SCC AS PSI DN encoded as a tel URI (see IETF RFC 3966 [42]) or SIP URI with the "user" SIP URI parameter set to "phone", in accordance with 3GPP TS 23.003 [4], subclause 13.5 as allocated in the above step 1and with the P-Asserted-Identity header field containing the E.164 number received in the a=cs-correlation attribute contained in the SDP offer in the SIP INVITE request received from the ICS UE then the SCC AS shall:
a) use the SCC AS PSI DN that was allocated to associate SCC-AS-PDN with the existing session and E.164 number received in the a=cs-correlation attribute contained in the SDP offer from the SIP INVITE request received from the ICS UE to correlate the SCC AS PSI DN with the existing session with the remote UE and acting as a routing B2BUA, generate SIP INVITE request and include the following information:
i) a Request-URI set to the contact address of the remote UE; and
ii) in the SDP add the SDP offer received from the received initial SIP INVITE request with the Request-URI containing the SCC AS PSI DN in accordance with the rules of IETF RFC 3264 [31].
Upon receiving a SIP 18x response from the remote UE the SCC AS shall send a SIP 18x response on the both leg with the ICS UE and on the leg with the CS domain. If the response from the remote UE includes an SDP answer, the SCC AS shall send an SDP answer on the leg with the ICS UE and on the leg with the CS domain. The SDP answers shall be in accordance with rules for SDP answer as specified in IETF RFC 3264 [31].
When the SCC AS is aware that preconditions are met on all legs, the SCC AS shall send a SIP UPDATE request on the leg with the remote UE indicating that local preconditions are met.
Upon receiving a SIP 200 (OK) response from the remote UE, the SCC AS shall send a SIP 200 (OK) response on both the leg with the ICS UE and on the leg with CS domain. The SCC AS may, based on operator policy, include a Feature-Caps header field defined in IETF RFC 6809 [48] with a "+g.3gpp.ics" header field parameter as described in clause B.4. If the SIP 200 (OK) response includes an SDP answer, the SCC AS shall send an SDP answer on the leg with the ICS UE and on the leg with the CS domain. The SDP answers shall be in accordance with rules for SDP answer as specified in IETF RFC 3264 [31].
When the SCC AS has received a SIP ACK request on both the leg with the CS domain and on the leg with the ICS UE, the SCC AS shall send a SIP ACK request to the remote UE.
8.4.3 SCC AS adds media in the PS domain
The SCC AS shall apply the procedure in accordance with 3GPP TS 24.229 [11].