Section: 4.3.23 Access network selection and traffic steering based on RAN-assisted WLAN interworking
Content: As described in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5], TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34], TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [37] and TS 25.331[ None ]  [33], UTRAN and E-UTRAN may provide RAN assistance parameters to the UE via RRC signalling. The RAN assistance parameters may e.g. include E-UTRAN signal strength and quality thresholds, WLAN channel utilization thresholds, WLAN backhaul data rate thresholds, a list of WLAN identifiers and Offload Preference Indicator (OPI). The UE uses the RAN assistance parameters to perform access network selection and traffic steering decisions between 3GPP access and WLAN using procedures defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34] or using ANDSF policies defined in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2]. Co-existence between the procedures defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34] and ANDSF policies is described in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2]. For traffic steering decisions using procedures defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34] the MME may provide information to the UE indicating which PDN Connection can be offloaded to WLAN and which PDN Connection shall not be offloaded to WLAN. When provided by the MME, this indication is provided in NAS signalling on a per PDN Connection basis when a PDN Connection is established. The MME may provide a per-RAT indication for the PDN connection, e.g. if the indication is different for UTRAN and for E-UTRAN. If the MME provides a single indication, the UE shall apply such indication both to E-UTRAN and UTRAN. Traffic steering decisions using procedures defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34] are not applicable to non-seamless WLAN offload (see TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2] for the definition of non-seamless WLAN offload). In order for the operator to allow/prohibit WLAN offloading on per user and per APN basis, subscription data in the HSS may be configured to indicate if WLAN offload is allowed or prohibited for an APN. The MME determines the WLAN offloading permissions for the UE and PDN Connection as described below: - The MME determines the offloadability of a PDN Connection based on subscription data and locally configured policy (e.g. for roaming users or when the subscription data does not include any WLAN offloadability indication). - When the UE establishes a new PDN Connection, the MME may indicate whether this PDN Connection is offloadable or not offloadable to WLAN. - The MME may provide an updated WLAN offloadability indication of a PDN Connection to the UE. This may be initiated by HSS as part of the Insert Subscriber Data procedure as described in clause 5.3.9.2. It can also be initiated by the MME by initiating steps 4 to 7 of the Bearer Modification Procedure in clause 5.4.3, Figure 5.4.3-1 or by adding the WLAN offloadability indication to a session management NAS message sent to the UE as part of an existing procedure. The MME shall not trigger signalling to an ECM-IDLE UE solely for the purpose of updating the WLAN offloadability indication. When the UE applies the procedures defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34] and TS 25.304[ None ]  [12], if the UE has Local Operating Environment Information (LOEI), as defined in TS 23.261[ IP flow mobility and seamless Wireless Local Area Network (WLAN) offload; Stage 2 ]  [54], the UE shall consider the RAN rules in combination with the non-radio related aspects of LOEI, and shall give priority to LOEI if it indicates WLAN is not acceptable for non-radio related reasons. For example, if the active RAN rule indicates that traffic shall be moved to WLAN access, but the LOEI in the UE indicates that WLAN access is unacceptable due to non-radio related causes (e.g. due to authentication issues, low battery power, etc.), the UE shall not move the traffic to WLAN. When the UE applies the procedures defined in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34], the UE takes into account the WLAN offloadability indication from MME to perform handover between 3GPP access and WLAN access using the handover procedures described in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2]. When the UE receives a WLAN offloadability indication from the network for a PDN connection the UE stores it for the lifetime of that PDN Connection and updates it if a new value is received from the network. The UE shall apply the latest indication previously received for the PDN Connection. The indication of whether a PDN connection is offloadable or not offloadable should be passed from the source to the target serving node in mobility management procedures from a MME to a MME/SGSN. This allows the target SGSN/MME to learn the indication previously provided to the UE and to decide the need for providing an updated indication to the UE.