This Study item is to study:

1. The addition of a S2a based on GTP option. In particular this SID will develop the necessary stage 2 message flows to support S2a based on GTP and mobility between GTP-S5/S8 and GTP-S2a.
2. Supporting WLAN access to EPC through S2a via mechanisms:
   • with no impact to the UE;
   • with impact to the UE.

Solutions requiring modifications to non 3GPP link-layers will not be considered. It is expected that the result of this Study Item may be used by 3GPP-BBF interworking activities (BBAI).

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.

The decision on whether a non 3GPP access is considered trusted or un trusted is made by the HPLMN operator and is not a characteristic of the non 3GPP access network. More details on it are provided in clause 4.3.1.2 of TS 23.402. The HPMN operator however while making a decision on trust worthiness of a non 3GPP access can also take into consideration security aspects of the access network. WLAN security was considered poor in both strength and ease of use, compared with that taken for granted in 3G networks and devices (UICC plus HSS, and GPRS encryption of data). Hence it made sense for the Mobile Network Operators (MNOs) to use their core network to add overlay security layers, i.e. the IKEv2 for Authentication and Authorization of the UE, and the IPSec between the UE and ePDG for the security of the user data. Now, with the deployment of 802.1x, 802.11u, 802.11i and Hotspot 2.0, it may be considered by some operators that the security strength and ease of use (discovery and set up) is as acceptable as 3G/LTE security. For example, for the radio air link, the operator controlled hotspot with 802.11i could be treated as a secure Non-3GPP Access. As 802.11i (or WPA2 called by WFA) has been released for several years, many AP-s support it as a basic feature and lots of smart phones also have supported it. WLAN can also be deployed integrated in a residential/enterprise device (e.g. femto). In such a scenario, protection mechanism for the traffic on the backhaul link between the residential/enterprise device and the EPC may be used. This protection of the backhaul may be leveraged to consider the WLAN security in terms of connectivity to the EPC. The impact on the support of the following scenarios shall be used to evaluate the solutions that will be proposed in the study:

• Access to EPC resources/services with access control by the operator;
• Seamless mobility between 3GPP and WLAN for EPS services with IP address preservation;
• Non-seamless mobility services between 3GPP and WLAN for EPS services: no IP address preservation;
• Support of UEs with single PDN connection; support of UEs with multiple PDN connections;
• Access to EPC via WLAN simultaneously with non-seamless WLAN offload.