4.1 High level WLAN architecture

32.2523GPPCharging managementRelease 9Telecommunication managementTSWireless Local Area Network (WLAN) charging

The WLAN – 3GPP interworking architecture is specified in 3GPP TS 23.234 [201]. It distinguishes between two interworking scenarios:

– WLAN Access, Authentication and Authorization, which provides for access to the WLAN and the locally connected IP network (e.g. Internet) to be authenticated and authorized through the 3GPP System. Access to a locally connected IP network from the WLAN, is referred to as WLAN Direct IP Access.

– WLAN 3GPP IP Access, which allows the WLAN UEs to establish connectivity with External IP networks, such as 3G operator networks, corporate Intranets or the Internet via the 3GPP system.

– WLAN Access Authentication and Authorisation and WLAN 3GPP IP Access are technically independent.

Figure 4.1.1 illustrates the basic WLAN networks from the point of view of 3GPP interworking.

Figure 4.1.1: Simplified WLAN Network Model
(the shaded area refers to WLAN 3GPP IP Access functionality)

The Packet Data Gateway supports WLAN 3GPP IP Access to External IP networks. The WLAN includes WLAN access points and intermediate AAA elements. It may additionally include other devices such as routers. The WLAN User Equipment (WLAN UE) includes all equipment that is in possession of the end user, such as a computer, WLAN radio interface adapter, etc.

Editor’s note: Appropriate mappings in clause 4 are needed, i.e. mapping between the logical charging functions as defined in 3GPP TS 32.240 and the WLAN charging entities.

Figure 4.1.2 depicts the non-roaming WLAN inter-working reference model for both Direct IP Access and 3GPP IP Access.

NOTE: The shaded area refers to WLAN 3GPP IP Access functionality.

Figure 4.1.2: Non Roaming Reference Model

Figure 4.1.3 depicts the roaming WLAN inter-working reference model where 3GPP PS based services are provided by the home PLMN based on 3GPP IP Access.

NOTE: The shaded area refers to WLAN 3GPP IP Access functionality.

Figure 4.1.3: Roaming reference model – 3GPP PS based services provided
via the 3GPP Home Network

Finally, figure 4.1.4 shows the case of the 3GPP IP Access PS based services being provided by the visited PLMN. Note that there is no difference between figures 4.3 and 4.4 for the case of WLAN Access, Authentication and Authorisation.

NOTE: The shaded area refers to WLAN 3GPP IP Access functionality.

Figure 4.1.4: Roaming reference model – 3GPP PS based services provided
via the 3GPP Visited Network

Detailed descriptions of nodes and reference points in figures 4.1.2, 4.1.3 and 4.1.4 are provided in 3GPP TS 23.234 [201]. Following is a short description of each. Coloured nodes and reference points are relevant for charging thus explained in more detail.

WLAN UE: a WLAN UE is the User Equipment using a UICC card utilized by a 3GPP subscriber to access the WLAN network for 3GPP interworking purpose.

WLAN Access Network (WLAN AN): WLAN AN provides the wireless IP connectivity to the WLAN UE. It generates per user charging information about the WLAN AN usage. WLAN AN is outside of 3GPP scope.

3GPP AAA Proxy: the 3GPP AAA Proxy represents a proxying and filtering function that resides in the Visited 3GPP Network, i.e. it exists only in the roaming case. For charging purposes the 3GPP AAA Proxy functions include:

– relaying the AAA information between WLAN and the 3GPP AAA Server;

– reporting per-user charging/accounting information to the VPLMN offline charging system for roaming users;

– protocol conversion when the Wa and Wd reference points do not use the same protocol. This function is dependent on inter-operator agreements;

For WLAN 3GPP IP Access only:

– Receiving per-tunnel charging information based on the tunnel identifier from the WAG and mapping of a user identifier and a tunnel identifier from the PDG; generating per user charging records for roaming users.

3GPP AAA Server: the 3GPP AAA server is located within the 3GPP HPLMN. It performs the AAA functions and may also act as an AAA proxy. For WLAN 3GPP IP Access it provides authorization, policy enforcement and routing information to the PDG, WAG and WLAN AN. For charging the 3GPP AAA Server:

– generates and reports per-user charging/accounting information to the HPLMN CDF;

– performs online charging control for the WLAN AN.

WLAN Access Gateway (WAG): the WAG applies to a WLAN 3GPP IP Access enabled system. It is a gateway via which the data to/from the WLAN Access Network is routed via the PLMN to provide a WLAN UE with 3G PS based services in a WLAN 3GPP IP Access enabled system. The WLAN Access Gateway resides in the VPLMN in the roaming case, and in the HPLMN in the non-roaming case. From charging point of view the WLAN Access Gateway:

– allows VPLMN to generate charging information for users accessing via the WLAN AN in the roaming case;

– performs collection of per tunnel accounting information, e.g. volume count (byte count) and elapsed time, to be used e.g. for inter-operator settlements.

NOTE 1: Per tunnel accounting generation in the WAG is not required when the WAG and PDG are in the same network.

Packet Data Gateway: the Packet Data Gateway (PDG) applies to a WLAN 3GPP IP Access enabled system. 3GPP PS based services are accessed via a PDG in the user’s Home Network or a PDG in the selected VPLMN. 3GPP PS based services may be accessed via a PDG in the user’s HPLMN or a PDG in the selected VPLMN. From charging point of view the Packet Data Gateway:

– generates charging information related to user data traffic for offline and online charging purposes;

– may apply IP flow based bearer level charging, e.g. in order to differentiate or suppress WLAN bearer charging for 3GPP PS based services.

Editor’s Note: PDG functionality may be provided by re-using the existing GGSN functionality. The current working assumption is that the TPF is a logical function allocated to the PDG providing IP flow based bearer level charging capabilities.

Following is a functional description of the reference points depicted in the above figures.

Wa: the Wa reference point connects the WLAN Access Network, possibly via intermediate networks, to the 3GPP Network (i.e. the 3GPP AAA Proxy in the roaming case and the 3GPP AAA server in the non-roaming case). The prime purpose of the protocols crossing this reference point is to transport authentication, authorization and charging-related information in a secure manner. The reference point has to accommodate also legacy WLAN Access Networks.

Wz: this reference point is used by the PDG for transfer of offline charging records from the PDG CDF to the CGF. The prime purpose of the protocols crossing this reference point is to transport/forward charging information towards 3GPP operator’s offline charging system, located in the VPLMN or HPLMN.

Wy: this reference point is an intra-operator interface used by the PDG to communicate with the Online Charging System. Wy is present when the PDG is located in the HPLMN (in the non-roaming case as described in figure 4.1.2 or in the roaming case with 3GPP PS based services provided via the 3GPP home network as described in figure 4.1.3). Wm, Wd, Wo are used instead in the roaming case with 3GPP PS based services provided via the 3GPP visited network as described in figure 4.1.4. The prime purpose of the protocol(s) crossing this reference point is to transport online charging related information so as to perform credit control for the online charged subscriber. This reference point applies the common 3GPP online charging interface as specified in 3GPP TS 32.299 [50].

Wm: this reference point applies to WLAN 3GPP IP Access.

The Wm reference point is located between

  • 3GPP AAA Server and Packet Data Gateway when the PDG is located in the HPLMN (in the non-roaming case as described in figure 4.1.2 or in the roaming case with 3GPP PS based services provided via the 3GPP home network as described in figure 4.1.3)
  • respectively between 3GPP AAA Proxy and Packet Data Gateway when the PDG is located in the VPLMN (in the roaming case with 3GPP PS based services provided via the 3GPP visited network as described in figure 4.1.4).

The functionalities of this reference point are described in 3GPP TS 23.234 [201].

Wo: the Wo reference point is used by the 3GPP AAA Server to communicate with 3GPP Online Charging System (OCS). The prime purpose of the protocol(s) crossing this reference point is to transport online charging related information so as to perform credit control for the online charged subscriber. This reference point applies the common 3GPP online charging interface as specified in 3GPP TS 32.299 [50].

Wf: the Wf reference point is located between the 3GPP AAA Server and 3GPP offline charging system. The prime purpose of the protocols crossing this reference point is to transport/forward charging information towards 3GPP operator’s offline charging system, located in the VPLMN or HPLMN, so as to generate CDRs for offline charged subscribers and to calculate inter-operator accounting.

The components of the "offline charging system" are further explained in clause 4.2.

This reference point applies the 3GPP Diameter based offline charging interface as specified in 3GPP TS 32.299 [50].

Wd: the Wd reference point applies to roaming cases only. The Wd reference point connects the 3GPP AAA Proxy, possibly via intermediate networks, to the 3GPP AAA Server. The prime purpose of the protocols crossing this reference point is to transport authentication, authorisation and related information. The functionality of the reference point is to transport AAA messages including charging signalling per WLAN user used for purging a user from the WLAN access for immediate service termination.

NOTE 2: Throughout the rest of the present current document, ‘Rf’ is used in place of ‘Wf’, and, ‘Ro’ is used in place of ‘Wo’ and ‘Wy’ for reasons explained in 3GPP TS 32.240 [1].