22B Xw Interface

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

22B.1 User Plane

The Xw user plane interface (Xw-U) is defined between eNB and WT. The Xw-U interface provides non guaranteed delivery of user plane PDUs. The user plane protocol stack on the Xw interface is shown in Figure 22B.1-1. The transport network layer is built on IP transport and GTP-U is used on top of UDP/IP to carry the user plane PDUs.

Figure 22B.1-1: Xw Interface User Plane

For LWA, if Xw-U user data bearers are associated with E-RABs for which the LWA bearer is configured, GTP-U conveys LWAAP PDUs and a RAN Container containing flow control information. The RAN Container is carried in the "RAN Container" field of the GTP-U extension header.

For the transfer of the uplink data, the WT may use either separate GTP-U tunnels as configured for each LWA bearer (based on the DRB Identity), or a single GTP-U tunnel. In the latter case, the WT shall use the tunnel associated with the lowest E-RAB ID.

22B.2 Control Plane

22B.2.0 General

The Xw control plane interface (Xw-C) is defined between an eNB and a WT. The control plane protocol stack of the Xw interface is shown on Figure 22B.2-1 below. The transport network layer is built on SCTP on top of IP. The application layer signalling protocol is referred to as Xw-AP (Xw Application Protocol).

Figure 22B.2-1: Xw Interface Control Plane

22B.2.1 Xw-CP Functions

The elementary functions supported by the Xw-AP protocol are listed in TS 36.463 [69].

22B.2.2 Xw-CP Procedures

The elementary procedures supported by the Xw-AP protocol are listed in TS 36.463 [69].

22B.2.2.1 WT Addition Preparation procedure

The WT Addition Preparation procedure is initiated by the eNB to request the WT to establish LWA bearer(s) for a specific UE.

Figure 22B.2.2.1-1: WT Addition Preparation procedure

The eNB sends a WT ADDITION REQUEST message to the WT including the LWA bearer(s) for the specific UE.

In case one or more GTP tunnel(s) at the WT has been established successfully, the WT responds with a WT ADDITION REQUEST ACKNOWLEDGE message, which includes successfully established and failed to be established bearers for LWA.

In case WT addition is not successful, the WT responds with WT ADDITION REQUEST REJECT message instead.

22B.2.2.2 WT Association Confirmation procedure

The WT Association Confirmation procedure is initiated by the WT to give confirmation to the eNB about the association establishment between a specific UE and the WLAN.

Figure 22B.2.2.2-1: WT Association Confirmation procedure

22B.2.2.3 eNB initiated WT Modification Preparation procedure

The eNB initiated WT Modification Preparation procedure is initiated by the eNB to request the WT to modify LWA bearer(s) for a specific UE at the WT.

Figure 22B.2.2.3-1: eNB initiated WT Modification Preparation procedure

The eNB sends a WT MODIFICATION REQUEST message to the WT including the LWA bearer(s) for the specific UE.

In case resource modification at the WT has been performed successfully, the WT responds with a WT MODIFICATION REQUEST ACKNOWLEDGE message.

In case the WT modification is not successful the WT responds with a WT MODIFICATION REQUEST REJECT message instead.

22B.2.2.4 WT initiated WT Modification procedure

The WT initiated WT Modification Preparation procedure is initiated by the WT to request the eNB to modify the WLAN resources for the specific UE.

Figure 22B.2.2.4-1: WT initiated WT Modification procedure

The WT sends a WT MODIFICATION REQUIRED message to the eNB to request to modify the WLAN resources for the specific UE.

If the WT modification is successful, the eNB replies with a WT MODIFICATION CONFIRM message.

22B.2.2.5 eNB initiated WT Release procedure

The eNB initiated WT Release procedure is triggered by the eNB to initiate the release of the resources for a specific UE at the WT.

Figure 22B.2.2.5-1: eNB initiated WT Release procedure

22B.2.2.6 WT initiated WT Release procedure

The WT initiated WT Release procedure is triggered by the WT to initiate the release of the resources for a specific UE at the WT.

Figure 22B.2.2.6-1: WT initiated WT Release procedure

The WT sends a WT RELEASE REQUIRED message to the eNB to request the release of the allocated WLAN resources for the specific UE.

If the WT release is successful, eNB replies with a WT RELEASE CONFIRM message.

22B.2.2.7 WT Status Reporting Initiation

The WT Status Reporting Initiation procedure is used by the eNB to request measurements from the WT.

Figure 22B.2.2.7-1: WT Status Reporting Initiation procedure

The eNB sends a WT STATUS REQUEST message to the WT to request measurements from the WT.

In case the requested measurements are successfully initiated, the WT responds with a WT STATUS RESPONSE message.

In case none of the requested measurements can be initiated, the WT responds with a WT STATUS FAILURE message instead.

22B.2.2.8 WT Status Reporting

The WT Status Reporting procedure reports measurement results requested by the eNB as described in 22B.2.2.7.

Figure 22B.2.2.8-1: WT Status Reporting procedure

22B.2.2.9 Xw Setup procedure

The purpose of the Xw Setup procedure initiated by the eNB is to exchange application level data needed for eNB and WT to interoperate correctly over the Xw interface. The Xw Setup procedure is triggered by the eNB. The Xw Setup procedure is the first Xw-AP procedure which will be executed.

Figure 22B.2.2.9-1: Xw Setup procedure

The eNB sends an Xw SETUP REQUEST message to the WT.

In case Xw setup has been performed successfully by the WT, the WT responds with an Xw SETUP RESPONSE message.

In case Xw setup is not successful, the WT responds with an Xw SETUP FAILURE message instead.

22B.2.2.10 WT Configuration Update procedure

The purpose of the WT Configuration Update procedure initiated by the WT is to update application level configuration data needed for the WT to interoperate correctly over the Xw interface.

Figure 22B.2.2.10-1: WT Configuration Update procedure

The WT sends a WT CONFIGURATION UPDATE message to the eNB.

In case WT Configuration Update procedure has been performed successfully by the eNB, the eNB responds with a WT CONFIGURATION UPDATE ACKNOWLEDGE message.

In case WT Configuration Update procedure is not successful, the eNB responds with a WT CONFIGURATION UPDATE FAILURE message instead.

22B.2.2.11 Error Indication procedure

22B.2.2.11.0 General

The Error Indication procedure is initiated by the eNB or the WT, to report an error situation in a received message, provided it cannot be reported by an appropriate failure message.

22B.2.2.11.1 WT initiated error indication

Figure 22B.2.2.11.1-1: Error Indication procedure initiated by WT

The WT sends the ERROR INDICATION message to report the eNB which kind of error occured.

22B.2.2.11.2 eNB initiated error indication

Figure 22B.2.2.11.2-1: Error Indication procedure initiated by eNB

The eNB sends the ERROR INDICATION message to report the WT which kind of error occured.

22B.2.2.12 Reset procedure

22B.2.2.12.0 General

The Reset procedure is initiated by the eNB/WT to align the resources with the WT/eNB in the event of an abnormal failure. The procedure resets the whole Xw interface.

22B.2.2.12.1 WT initiated reset

Figure 22B.2.2.12.1-1: Reset procedure initiated by WT

The WT triggers the RESET message to indicate that an initialisation in the eNB is required. The eNB releases the corresponding references and resources.

Afterwards the eNB sends the RESET RESPONSE message to confirm that the resources and references are cleared.

22B.2.2.12.2 eNB initiated reset

Figure 22B.2.2.12.2-1: Reset procedure initiated by eNB

The eNB triggers the RESET message to indicate that an initialisation in the WT is required. The WT releases the corresponding references and resources.

Afterwards the WT sends the RESET RESPONSE message to confirm that the resources and references are cleared.

22B.2.2.13 LWIP Addition Preparation procedure

The LWIP Addition Preparation procedure is initiated by the eNB to request the LWIP-SeGW to establish LWIP bearer for a specific UE.

Figure 22B.2.2.13-1: LWIP-SeGW Addition Preparation procedure

The eNB sends a LWIP ADDITION REQUEST message to the LWIP-SeGW including security information for the specific UE.

In case the GTP tunnel at the LWIP-SeGW has been established successfully, the LWIP-SeGW responds with a LWIP ADDITION REQUEST ACKNOWLEDGE message.

In case LWIP-SeGW Addition is not successful, the LWIP-SeGW responds with LWIP ADDITION REQUEST REJECT message instead.

22B.2.2.14 eNB initiated LWIP Modification Preparation procedure

The eNB initiated LWIP Modification Preparation procedure is initiated by the eNB to request the LWIP-SeGW to modify resources for a specific UE at the LWIP-SeGW.

Figure 22B.2.2.14-1: eNB initiated LWIP-SeGW Modification Preparation procedure

The eNB sends a LWIP MODIFICATION REQUEST message to the LWIP-SeGW including requested modifications.

In case resource modification at the LWIP-SeGW has been performed successfully, the LWIP-SeGW responds with a LWIP MODIFICATION REQUEST ACKNOWLEDGE message.

In case the LWIP-SeGW modification is not successful the LWIP-SeGW responds with a LWIP MODIFICATION REQUEST REJECT message instead.

22B.2.2.15 eNB initiated LWIP Release procedure

The eNB initiated LWIP Release procedure is triggered by the eNB to initiate the release of the resources for a specific UE at the LWIP-SeGW.

Figure 22B.2.2.15-1: eNB initiated LWIP-SeGW Release procedure

22B.2.2.16 LWIP-SeGW initiated LWIP Release procedure

The LWIP-SeGW initiated LWIP Release procedure is triggered by the LWIP-SeGW to initiate the release of the resources for a specific UE at the LWIP-SeGW.

Figure 22B.2.2.16-1: LWIP-SeGW initiated LWIP-SeGW Release procedure

The LWIP-SeGW sends a LWIP RELEASE REQUIRED message to the eNB to request the release of the allocated WLAN resources for the specific UE.

If the LWIP-SeGW release is successful, eNB replies with a LWIP RELEASE CONFIRM message.