3 Definitions, symbols and abbreviations
23.2373GPPIP Multimedia Subsystem (IMS) Service ContinuityRelease 17Stage 2TS
3.1 Definitions
For the purposes of the present document, the terms and definitions in TR 21.905 [1] and the following apply.
5G-SRVCC: See TS 23.216 [10].
Access Leg: This is the call control leg between the UE and the SCC AS; also see TS 23.292 [5] for the definition of Access Leg for IMS sessions which use the CS media.
Access Transfer: Transfer at the IMS-level of one or more media paths of an ongoing IMS session on one UE between PS to CS access; or transfer at the IMS-level of both the signalling and the media path of an ongoing IMS session on a UE between different IP-CANs.
Collaborative Session: A set of two or more Access Legs and related media on two or more UEs having IMS subscriptions under the same operator that are presented as one Remote Leg by the SCC AS.
Collaborative Session Control: The control operations on the Collaborative Session which can only be performed by the Controller UE, e.g. ability to release the Collaborative Session, to invoke supplementary services, and to authorize requests for IUT Media Control Related Procedures from other UEs.
Controllee UE: A UE that supports media flows for a Collaborative Session and may request IUT Media Control Related Procedures but is subordinate to the Controller UE for authorization of these procedures.
Controller UE: The UE that controls a Collaborative Session and whose service profile determines the services on the remote leg. The Controller UE may also support media flows for a Collaborative Session and may request IUT Media Control Related Procedures.
Correlation MSISDN: An MSISDN used for correlation of sessions. See TS 23.003 [14] for more information.
Dual Radio: This refers to the situation where the UE is capable to transmit/receive on two different radio access technologies simultaneously.
eCall: See TS 22.101 [9].
Emergency Session Transfer Number for SRVCC: A number used in the session transfer procedure for emergency calls, pointing toward the serving (visited if roaming) IMS EATF which handles the IMS emergency session transfer from PS to CS access.
Emergency Session Transfer Number for DRVCC: A number used by the UE to request the EATF AS to perform Session Transfer from PS to CS access. The E-STN-DR is dynamically assigned by EATF during IMS emergency session procedure with WLAN.
Hosting SCC AS: The SCC AS that manages the dialog with the remote party for a Collaborative Session.
IMS Service Continuity: A service of the IMS which supports the use of Session Transfer mechanisms to maintain service continuity in the event of terminal mobility and/or mobility between terminals for the case when such events are not hidden from the IMS session layer and thus service continuity could not otherwise be maintained.
Inter-UE Transfer: Transfer at the IMS-level of some or all of the media flows and/or service control across a set of having IMS subscriptions under the same operator.
NOTE 1: The transfer of all media flows and the control signalling from one UE to another is also known as Session Mobility as defined in TS 22.258 [2].
IP Multimedia Routing Number (IMRN): An IP Multimedia Routeing Number (IMRN) is a routable number that points to an SCC AS in the IM CN subsystem. See TS 23.003 [14] for more information.
IUT Media Control Related Procedures: The control operations on the media flows of the Collaborative Session which involve multiple UEs or need Controller UE’s authorization within the Collaborative Session, e.g. ability to transfer/add/replicate media flows, to remove/modify media flows on a different UE.
Local Operating Environment Information: This is a set of parameters, which can include access network(s) conditions and other parameters implementation specific, which describe the local environment in which the UE is operating.
Minimum Set of Data (MSD): See TS 22.101 [9].
MSC Server assisted mid-call feature: Functionality of the MSC Server, the SCC AS and the UE, enabling PS – CS Access Transfer for UEs not using ICS capabilities, while preserving the provision of mid-call services (inactive sessions or sessions using the Conference service).
NOTE 2: This terminology is often abbreviated as "mid-call feature" or even "mid-call" throughout this specification.
NG-RAN: See TS 23.216 [10].
Pre-alerting state: This is the state where the UE can receive early media in the early dialogue phase.
Remote Leg: This is the call control leg between the SCC AS and the remote party from the subscriber’s perspective; also see TS 23.292 [5] for the definition of Remote Leg for IMS sessions which use the CS media.
Service Control Signalling Path: As defined in TS 23.292 [5].
Session Replication: Replication, at the IMS-level, of a session ongoing in a source UE at a target UE. When the new, independent, session is established at the target UE, the state of the original media is replicated e.g. same playback state; same used media etc. is replicated.
Session State Information: Information of IMS session state sent by the SCC AS for enablement of PS-CS and CS-PS Access Transfer of IMS multimedia-sessions when ICS UE capabilities can not be used.
Session Transfer: Transfer at the IMS-level of one or more of the session signalling paths and/or associated media flow paths of an ongoing IMS session while maintaining service continuity. Session Transfer incorporates Access Transfer and / or Inter-UE Transfer.
Session Transfer Identifier (STI): An identifier used by the UE to request the SCC AS to perform Session Transfer. The STI is either statically configured on the UE or dynamically assigned. See TS 23.003 [14] for more information.
Session Transfer Identifier for reverse SRVCC (STI-rSR): A dynamic identifier used by the UE to request the IMS network to perform Session Transfer for CS to PS SRVCC (reverse SRVCC). The STI-rSR is used by the network to correlate two access legs, and is unique for each access transfer control function within an ATCF.
Session Transfer Number (STN): A number used by the UE to request the SCC AS to perform Session Transfer from PS to CS access. The STN is configured and stored on the UE and can be updated with current address during session establishment. See TS 23.003 [14] for more information.
Session Transfer Number for SRVCC (STN-SR): A STN used for SRVCC procedures as specified in TS 23.216 [10]. STN-SR is a subscription information provided to HSS for each subscriber if SRVCC service is allowed by hPLMN. STN-SR is a routing number indicating the SCC-AS or the ATCF if SRVCC enhanced with ATCF or if 5G-SRVCC is used. See TS 23.003 [14] for more information.
Single Radio: This refers to the situation where the UE is only capable of transmitting/receiving on one radio access technology at a time.
Source Access Leg: The Access Leg that exists in the transferred-out access before executing Access Transfer procedures.
Target Access Leg: The Access Leg that is established in the transferred-in access during Access Transfer procedures.
UDM: See TS 23.216 [10].
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1].
3pcc 3rd party call control
ATCF Access Transfer Control Function
ATGW Access Transfer Gateway
ATU-STI Access Transfer Update – Session Transfer Identifier
C-MSISDN Correlation MSISDN
DRVCC Dual Radio Voice Call Continuity
EATF Emergency Access Transfer Function
E-STN-DR Emergency Session Transfer Number for DRVCC
iFC Initial Filter Criteria
IMRN IP Multimedia Routing Number.
IUT Inter-UE Transfer
MSD Minimum Set of emergency related Data
OCS Online Charging System
SC Service Continuity
SCC AS Service Centralization and Continuity Application Server
SRVCC Single Radio Voice Call Continuity
STI Session Transfer Identifier
STI-rSR Session Transfer Identifier for CS to PS SRVCC
STN Session Transfer Number
STN-SR Session Transfer Number – Single Radio
E-STN-SR Emergency Session Transfer Number for SRVCC