10 RAN assisted WLAN interworking

25.3003GPPGeneral descriptionRelease 17Stage 2TSUniversal Terrestrial Radio Access Network (UTRAN)

This clause describes the mechanisms to support traffic steering between UTRAN and WLAN.

10.1 General principles

This version of the specification supports UTRAN assisted UE based bi-directional traffic steering between UTRAN and WLAN for UEs in Idle mode and CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH states.

UTRAN provides assistance parameters via broadcast and dedicated RRC signalling to the UE. The RAN assistance parameters may include UTRAN signal strength thresholds, WLAN channel utilization thresholds, WLAN backhaul data rate thresholds, WLAN signal strength thresholds and Offload Preference Indicator (OPI). UTRAN can also provide a list of WLAN identifiers to the UE via broadcast and dedicated signalling.

The UE uses the RAN assistance parameters in the evaluation of:

– access network selection and traffic steering rules defined in TS 25.304 [9]; or

– ANDSF policies defined in TS 24.312 [8]

for traffic steering decisions between UTRAN and WLAN as specified in TS 23.402 [10].

The OPI is only used in ANDSF policies as specified in TS 24.312 [8].

WLAN identifiers are only used in access network selection and traffic steering rules defined in TS 25.304 [9].

If the UE is provisioned with ANDSF policies it shall forward the received RAN assistance parameters to upper layers, otherwise it shall use them in the access network selection and traffic steering rules defined in subclause 10.2 and TS 25.304 [9]. The access network selection and traffic steering rules defined in subclause 10.2 and TS 25.304 [9] are applied only to the WLANs of which identifiers are provided by the UTRAN.

The UE in CELL_DCH state shall apply the parameters obtained via dedicated signalling, and shall keep those parameters during handover if they are not reconfigured or deleted; the UE shall discard the parameters obtained via dedicated signalling at SRNS relocation.

The UE in CELL_FACH state shall apply the parameters obtained via dedicated signalling if such have been received from the serving cell; otherwise the UE shall apply the parameters obtained via broadcast signalling. Upon cell selection/reselection the UE shall discard the dedicated parameters.

The UE in Idle mode, CELL_PCH or URA_PCH state shall keep and apply the parameters obtained via dedicated signalling until selection/reselection of another cell than the one where these parameters were received or a timer has expired since the UE moved from CELL_DCH or CELL_FACH to Idle mode, CELL_PCH or URA_PCH state, upon which the UE shall discard the dedicated parameters and apply the parameters obtained via broadcast signalling.

In the case of RAN sharing, each PLMN sharing the RAN can broadcast independent sets of RAN assistance parameters.

10.2 Access network selection and traffic steering rules

The UE indicates to upper layers when (and for which WLAN identifiers) access network selection and traffic steering rules defined in TS 25.304 [9] are fulfilled. The selection among WLANs that fulfil the access network selection and traffic steering rules is up to UE implementation.

When the UE applies the access network selection and traffic steering rules defined in TS 25.304 [9], higher layers perform traffic steering between UTRAN and WLAN.