The present document specifies service requirements for Combining CS and IMS services using a CS speech or CS multimedia call in association with an IMS session. The IMS session may consist of one or more IMS services.
Requirements for the following capabilities are included:
Radio capability exchange.
Terminal capability exchange.
E.164 number exchange.
Adding IMS session to an ongoing CS call.
Adding a CS call to an ongoing IMS session.
Supplementary services as they relate to CSICS.
It is intended that the capabilities defined herein for CSICS shall support interoperability between different operator networks, and roaming.
The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
For a specific reference, subsequent revisions do not apply.
For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
 TR 21.905
: "Vocabulary for 3GPP Specifications".
 TR 22.979
: "Feasibility study on Combined CS Calls and IMS Sessions".
 TS 22.228
: "Service requirements for the Internet Protocol (IP) multimedia core network subsystem".
 TS 22.004
: "General on Supplementary Services".
Combinational services are applicable to both UTRAN and GERAN and enables the unidirectional or bi-directional exchange of PS data within the context of an IMS session
A specific subscription for combinational services is not necessary. However, both users A and B shall as a minimum be provisioned with CS telephony (TS11) as well as for accessing the IMS.
The existing address context is reused when the combined service is established, which makes the combined service simple to invoke for the user.
In addition to the existing IMS requirements , the following general requirements apply for CSICS:
It shall be possible to establish a combinational service between two users within the same PLMN or within different PLMNs.
It shall be possible to establish a combinational service between two users camped on identical or different RATs.
It shall be possible to establish a combinational service when roaming, assuming the visited operator supports GPRS roaming.
The user (A or B party) shall only need to know one address in order to establish the combinational service.
It shall be possible to add an IMS session to a CS speech call, thereby creating a combinational call.
It shall be possible to add a CS speech call to an IMS session, thereby creating a combinational session.
It shall be possible to add an IMS session to a CS Multimedia call, thereby creating a combinational call.
It shall be possible to add a CS Multimedia call to an IMS session, thereby creating a combinational session.
The following two service modes will exist in regards to IMS registration depending on different UE implementations:
IMS pre established state: the CSICS capable UE performs the IMS registration at switch on.
IMS on demand state: the CSICS capable UE performs the IMS registration:
to start the communication, or
to add a IMS session to an existing CS call.
Interoperability between UEs that implement such different approaches shall be enabled.
During a CS call it shall be possible to request establishment of the IMS session whether the invited UE is IMS registered or not. The invited user shall be able to accept or reject the IMS registration request.
A combinational service shall enable both unidirectional and bi-directional exchange of PS data within the context of the IMS session.