The present document investigates relevant scenarios and possible solutions to enhance the CS/PS Coordination in a shared UTRAN/GERAN network as currently specified in TS 23.251. Within this technical report relevant mobility scenarios shall be investigated and it shall be evaluated per scenario if any issues with CS/PS Coordination can be expected. The investigation shall be done for non-supporting UEs and for any UE in shared networks where no Multiple PLMN list is broadcasted. Solutions to solve found issues shall be evaluated and agreed for subsequent normative specification. The scenarios that need to be handled will at least include:

• CS handover to UTRAN/GERAN (DTM/non-DTM for GERAN);
• PS Handover to UTRAN/GERAN (DTM/non-DTM for GERAN);
• Redirection;
• Cell reselection;
• CSFB;
• rSRVCC and SRVCC;
• PLMN selection at handover based on UE capability;
• Registration to PS domain in a shared network after CS only registration has been performed.

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.

In conventional networks, the same CN operator always serves the UE in CS and PS domains. In a shared network the same conclusion is valid as for conventional networks with respect to registration with CS and PS domains and the UE shall always register with the same operator for the CS and PS domains. If the CS/PS coordination fails i.e. separate CS and PS requests are accepted by different sharing operators, the UE will receive a TMSI pointing to one sharing operator and a P-TMSI pointing to another sharing operator. In both cases the Common PLMN will be used, so for basic connectivity and service there should be no problem. The RAN will route subsequent messages based on the temporary identifiers. From the sharing operator's point of view the UE will be registered and receive service for either CS only or PS only. Charging will be received from separate operators for CS and PS. Additional affects from incorrect CS/PS coordination are:

1. The network name presented to the end user will be according to the name corresponding to the Common PLMN. If Network Identity and TimeZone (TS 22.042) is used to provide an the operator name to the UE for displaying to the user, either the network providing CS service or the network providing PS service will be displayed depending on which domain registration is completed successfully last. Thus, it is unpredictable which name will be displayed.
2. The tariff information sent to the UE e.g. via SMS, if any, will come from the home operators. The information may come separate for CS and for PS services. If the tariffs from both serving operators differ, the end user will assume the tariff of the displayed network applies. The consequence in such a cases is that the end user will assume being charged according to one tariff while in reality charged according to the tariff of another operator. However a more likely scenario may be that the roamed to tariffs are identical for all permitted networks in a country.
3. The equivalent PLMN list used will be provided by one operator and it is unpredictable which as the latest received will be used by the UE. The equivalent PLMN list can change back and forth between the list provided by the CS domain operator and the PS domain operator, and it is thus unpredictable what PLMN the UE can reselect to if e.g. reselecting to LTE.
4. When operators are not using coordinated NRIs between different networks, between different areas within a shared network or if NRI coordination method is used but the UE provided NRI is from an area or network that doesn't belong to the coordinated NRIs or an NRI is absent, the network-initiated CS/PS coordination process is used as part of UE mobility procedures between such areas or networks. This process guarantee the coordination of UE's serving operator in the target CS and PS domains but may result in change of the serving CN operator for the UE compared to the CN operator used before the mobility procedure. For Visited-GGSN/PDNWG roaming this will imply a change of user IP address, which may in turn have end-user service impacts (many applications can handle a change of IP address but this is not always true) and result in negative effects on the user perception of operators sharing networks. Frequent mobility events for which the network-initiated CS/PS coordination process is evoked may lead to excessive signalling, for example between UEs and application servers to handle the change of the UE's IP address.