For networks deploying a single IP mobility management mechanism, the statically configured mobility mechanism can be access type and/or roaming agreement specific. The information about the mechanism to be used in such scenario is expected to be provisioned into the terminal (or the UICC) and the network. IP session continuity between 3GPP and non-3GPP access types may not be provided in this case if there is a mismatch between what the UE expects and what the network supports. For example service continuity may not be possible if the user switches to a terminal supporting a different IP mobility management mechanism than provisioned in the network.

IP Mobility management Selection (IPMS) consist of two components:

• IP MM protocol selection between Network Based Mobility (NBM) and Host based mobility (HBM - MIPv4 orDSMIPv6).
• Decision on IP address preservation if NBM is selected.

IPMS does not relate to the selection between PMIPv6 and GTP over S5/S8/S2b/S2a. Upon initial attachment to a 3GPP access, no IPMS is necessary since connectivity to a PDN-GW is always established with a network-based mobility mechanism. Upon initial attachment to a trusted non-3GPP access or ePDG and upon handover from 3GPP to a trusted non-3GPP access or ePDG, IPMS is performed before an IP address is allocated and provided to the UE. The UE support for a specific IP Mobility Management protocol and/or IP address preservation mechanism for inter-access mobility may be known by the network-based on explicit indication from the UE. Upon attachment to a trusted non-3GPP access or ePDG, if the access network (supporting at least NBM) is not aware of the UE capabilities and the home and access network's policies allow the usage of NBM, then NBM is used for establishing connectivity for the UE to the EPC. When a NBM mechanism is used for establishing connectivity in the target access upon inter-access mobility, IP address preservation for session continuity based on NBM may take place as per PMIPv6 specification (RFC 5213) or according to clause 8.6 for GTP, and additionally based on the knowledge in the network of UE's capability (if available) to support NBM. Such knowledge may be based on an explicit indication from the UE upon handover that IP address preservation based on NBM management can be provided. IP address preservation for session continuity based on HBM may take place if the network is aware of the UE capability to support DSMIPv6 or MIPv4. Such knowledge may be based on an indication to the target trusted non-3GPP access or ePDG from the HSS/AAA (e.g. in case of DSMIPv6, the UE performed S2c bootstrap before moving to the target trusted non-3GPP access or ePDG). In such a case, the trusted non-3GPP access network or ePDG provides the UE with a new IP address, local to the access network if IP mobility management protocol selected is DSMIPv6. In that case, in order to get IP address preservation for session continuity, the UE shall use DSMIPv6 over S2c reference point. This IP address shall be used as a care-of address for DSMIPv6. If the IP mobility management protocol selected is MIPv4, the address provided to the UE by the non-3GPP access network is a FACoA and IP address preservation is performed over S2a using MIPv4 FACoA procedures. The final decision on the mobility management mechanism is made by the HSS/AAA upon UE authentication in the trusted non-3GPP access system or ePDG (both at initial attachment and handover), based on the information it has regarding the UE, local/home network capabilities and local/home network policies. If the UE provided an explicit indication of the supported mobility mechanisms, the network shall provide an indication to the UE identifying the selected mobility management mechanism. Support of different IP mobility management protocols at local/home network is known by the AAA/HSS in one of the following ways:

• through static pre-configuration, or
• through indication of the supported IP mobility management protocols (NBM and/or MIPv4 FA CoA mode) by the trusted non-3GPP access system or ePDG as part of the AAA exchange for UE authentication.

Upon selecting a mobility management mechanism, as part of the AAA exchange for UE authentication in the trusted non-3GPP access system or ePDG, the HSS/AAA returns to the trusted non-3GPP access system or ePDG an indication on whether a local IP address shall be allocated to the UE, or if instead NBM shall be used to establish the connectivity, or the HSS/AAA returns to the trusted non-3GPP access system an indication that the address of the MIPv4 Foreign Agent shall be provided to the UE. IPMS is performed in the following scenarios:

• Upon initial attach to a trusted non-3GPP access or ePDG, the IPMS is performed to decide how to establish IP connectivity for the UE.
• Upon handover without optimization from a 3GPP access to a non-3GPP access, the IPMS is performed to decide how to establish IP connectivity for the UE over the trusted non-3GPP access or ePDG.
• Upon change of access between a non-3GPP access and a 3GPP access or between two non-3GPP accesses, if the IP MM protocol used to provide connectivity to the UE over the trusted non-3GPP access or ePDG is a NBM protocol, then a decision is performed on whether IP address preservation is provided or not as per PMIPv6 specification, (RFC 5213) or according to clause 8.6 for GTP and additionally based on the knowledge in the network of UE's capability (if available) to support NBM.