22A.2 RAN Controlled LTE WLAN Interworking

36.3003GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)Overall descriptionRelease 17Stage 2TS

22A.2.1 General

E-UTRAN supports E-UTRAN controlled bi-directional traffic steering between E-UTRAN and WLAN for UEs in RRC_CONNECTED: RAN Controlled WLAN Interworking (RCLWI). E-UTRAN may send a steering command to the UE indicating to steer traffic from E-UTRAN to WLAN or from WLAN to E-UTRAN. The upper layers in the UE shall be notified (see TS 24.302 [67]) upon reception of such a command. Upper layers determine which traffic is offloadable to WLAN. Similarly as for LWA, two scenarios are supported depending on the backhaul connection between LTE and WLAN (non-collocated RCLWI scenario for a non-ideal backhaul and collocated RCLWI scenario for an ideal/internal backhaul), and the overall architecture for the non-collocated RCLWI scenario is the same as illustrated for LWA in Figure 22A.1.1-1 above.

If the UE supporting RCLWI supports access network selection and traffic steering rules defined in TS 36.304 [11], the UE applies the rules in RRC_IDLE using WLAN identifiers provided in WLAN mobility set. If the UE supporting RCLWI and traffic steering rules defined in TS 36.304 [11], has not been configured with a WLAN mobility set, it applies the broadcasted WLAN identifiers. If the UE supporting RCLWI does not support the traffic steering rules defined in TS 36.304 [11], it keeps traffic on WLAN within the configured WLAN mobility set (if any) in RRC_IDLE until WLAN connection fails.

E-UTRAN does not configure RCLWI with DC, LWA or LWIP simultaneously for the same UE.

If RCLWI and RAN assisted WLAN interworking are simultaneously configured for the same UE, in RRC_CONNECTED, the UE only applies RCLWI.

22A.2.2 Network Interfaces

22A.2.2.1 General

Similarly as for LWA, in the non-collocated RCLWI scenario, the eNB is connected to one or more WT logical nodes via an Xw interface and in the collocated RCLWI scenario the interface between LTE and WLAN is up to implementation.

22A.2.2.2 User Plane Plane

There is no user plane interface defined between the eNB and the WT in RCLWI.

22A.2.2.3 Control Plane

In the non-collocated RCLWI scenario, the Xw control plane interface (Xw-C) is defined between the eNB and the WT and is similar to what is defined for LWA in clause 22A.1.3.3. LWA specific funtions are not part of RCLWI.

22A.2.3 Mobility

A WLAN mobility set is a set of one or more BSSID/HESSID/SSIDs, within which WLAN mobility mechanisms apply while the UE has moved offloadable traffic to WLAN according to a steering command, i.e. the UE may perform mobility between WLAN APs belonging to the mobility set without informing the eNB.

22A.2.4 WLAN Measurements

The UE supporting RCLWI may be configured by the E-UTRAN to perform WLAN measurements. WLAN measurement object can be configured using WLAN identifiers (BSSID, HESSID and SSID), WLAN carrier information and WLAN band. WLAN measurement reporting is triggered using RSSI. WLAN measurement report contains, for each included WLAN, RSSI and WLAN identifier, and may contain WLAN carrier information, WLAN band, channel utilization, station count, admission capacity, backhaul rate and an indication whether the UE is connected to the WLAN.

22A.2.5 Procedure for WLAN Connection Status Reporting

The purpose of the WLAN Connection Status Reporting procedure is to provide feedback to the eNB related to the WLAN status and operation. The WLAN Connection Status Reporting procedure supports the following indications:

1. Failure of establishing/maintaining a WLAN connection.

When a UE configured to offload to WLAN becomes unable to establish or continue WLAN offloading, the UE sends the WLANConnectionStatusReport message to indicate to the eNB that the WLAN connection failed and the UE moves all the offloaded traffic to E-UTRAN (see TS 24.302 [67]).

The criteria to determine WLAN connection failure is left for UE implementation.

22A.2.6 Traffic Steering Operation

22A.2.6.1 Traffic Steering from E-UTRAN to WLAN

The traffic steering from E-UTRAN to WLAN procedure is initiated by the eNB.

Figure 22A.2.6.1-1: Traffic steering from E-UTRAN to WLAN procedure

1. The eNB sends the RRCConnectionReconfiguration message to the UE indicating the UE to steer traffic from E-UTRAN to WLAN.

2. The UE forward the indication to upper layers and replies with RRCConnectionReconfigurationComplete message.

3. The UE performs WLAN Association and after successful connection to WLAN, steers traffic from E-UTRAN to WLAN (subject to upper layer).

4. If WLAN association failed, the UE sends WLANConnectionStatusReport message.

22A.2.6.2 Traffic Steering from WLAN to E-UTRAN

The traffic steering from WLAN to E-UTRAN procedure is initiated by the eNB.

Figure 22A.2.6.2-1: Traffic steering from WLAN to E-UTRAN procedure

1. The eNB sends the RRCConnectionReconfiguration message to the UE indicating the UE to steer traffic fromWLAN to E-UTRAN.

2. The UE forward the indication to upper layers and replies with RRCConnectionReconfigurationComplete message.

3. The UE steers traffic from WLAN to E-UTRAN.