The Evolved Packet System shall support mobility between heterogeneous access systems. The Evolved Packet System shall provide mobility mechanisms to support frequent handovers within and across 3GPP legacy systems or E-UTRAN and non 3GPP access systems in order to avoid service degradation. The Evolved Packet System shall support mobility mechanisms that accommodates access systems within Rel-7 and earlier.

The Evolved Packet System shall allow for local breakout. Local breakout means that for a user which makes mobility within and across one operator-defined network region, routing is optimized such that user plane traffic does not need to leave the current region. An operator may define network regions e.g., according to administrative domains. Local breakout is applicable for user-to-user traffic as well as for 3GPP-operator provided services (including internet access). Local breakout shall be allowed independently from the access system being used. Local breakout shall be allowed in both the non-roaming and the roaming case. The use of local breakout shall be authorised by the HPLMN. If local breakout is not authorised, the user plane traffic shall be handled in the home routed mode.

The Evolved Packet System shall be able to support fixed access systems with very limited or no mobility functionality. The Evolved Packet System shall be able to support mobility within and across 3GPP and non-3GPP access systems including fixed access systems

To avoid unnecessary background scan by the UE and to facilitate service continuity by the UE it shall be possible for the VPLMN and the HPLMN to provide the UE with access network information pertaining to locally supported non-3GPP access technologies, in a resource efficient and secure manner. This mechanism is meant to facilitate changes, including service continuity, between 3GPP access systems and non 3GPP access systems and vice versa. The information may be restricted to the access technologies the UE can use. To reduce battery drain, a UE should minimise the frequency of scanning for different access technologies. When discovering non-3GPP accesses a UE shall be able to receive information from a non-3GPP access network concerning to which PLMN, or PLMNs, the non-3GPP access network provides access. When a UE receives service via a non-3GPP access it shall be possible for the PLMN that provides the non-3GPP access to indicate local availability of 3GPP access to the UE,, in a secure manner, subject to capabilities of the non-3GPP access network.

When a UE is accessing the Evolved Packet Core via E-UTRA, the operator of the PLMN that provides the access (registered PLMN or RPLMN for short) may request the UE to use - any or a specific - non-3GPP RAT. Similarly, if a UE is accessing the Evolved Packet Core via a non-3GPP RAT then the RPLMN may want to request the UE to use E-UTRA. The reason for such steering may be load balancing (for camped- and traffic load balancing), operator policy, private networks/home cells, service based mobility control etc. The RPLMN shall be able to download on the UE a list of preferred access technologies in priority order. If, while the UE is registered on that PLMN, an access technology with higher priority than the one currently used is detected, the UE shall attempt to use the higher priority access network to access the RPLMN. The UE shall only perform access technology selection within the RPLMN. In case the UE is connected to the PLMN via a non-3GPP access, then the PLMN reselection procedures specified for that access technology may be executed. The HPLMN may also provide the UE with a list of preferred access technologies in priority order for use in the RPLMN. Only one list of preferred access technologies can be active at a time and the list provided by the RPLMN takes precedence over the list provided by the HPLMN. The list of preferred access technologies received from the VPLMN is specific to that VPLMN and PLMNs equivalent to it.

The Evolved Packet System may provide functionality to enable user access to PLMN IP-based services from outside of the PLMN's domain via non-3GPP access technologies under conditions where there are IP traffic-flow restrictions (e.g. allow only HTTP traffic). Such functionality is known as Service Reachability. When the Evolved Packet System provides Service Reachability, the following requirements apply:

• pre-existing EPS security shall be maintained; and
• the third party that placed the IP traffic-flow restriction shall be able to prohibit Service Reachability by blocking PLMN IP-based services intentionally.