3GPP WLAN Interworking Reference Model
The network devices that make up a 3GPP WLAN network are called network elements. Each network element performs a specific function. Network elements communicate with each other over reference points. This section provides a brief overview of the 3GPP WLAN reference model. For complete details, refer to the appropriate 3GPP specification.
The section provides a brief description of the 3GPP WLAN reference model network elements.
(Wireless Local Area Network's User Equipment) This network element represents the equipment, such as a mobile phone, used by the subscriber to access the WLAN infrastructure. This device has a UICC card (universal integrated circuit card) used by a 3GPP subscriber to access the WLAN AN for 3GPP interworking purposes.
The Wireless LAN Access Network provides the wireless IP connectivity to the WLAN UE so that requests from the WLAN UE can be authenticated and authorized by the 3GPP AAA server in the 3GPP network. When the WLAN AN receives a subscriber's connection request, it may perform an initial access negotiation with the subscriber to obtain identity information and then pass this information to the 3GPP AAA server as part of an authentication/authorization request. The WLAN AN is a client from the perspective of the 3GPP AAA Server, and may be either RADIUS or Diameter- based.
3GPP AAA Server
The 3GPP AAA server is located within the 3GPP HPLMN. It performs the AAA functions and may also act as a AAA proxy server. 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 charging/accounting information to the CDF.
- Performs offline charging control for the WLAN AN.
- Performs RADIUS to Diameter and Diameter to RADIUS protocol conversion when necessary.
The WLAN Access Gateway performs a function similar to a firewall that limits the IP connectivity of WLAN users. Filter rules are pushed to it from the 3GPP network.
The Packet Data Gateway performs authentications and authorizations for tunnel requests, when tunneled IP service (WLAN 3GPP IP Access) is being provided. 3GPP PS (Packet Switched) services are accessed through a PDG in the subscriber's HPLMN (Home Public Land Mobile Network) or a PDG in the selected VPLMN. From charging point of view the PDG:
- Generates charging information related to subscriber data traffic for offline and online charging purposes.
The Subscription Location Function is located within the 3GPP subscriber's home network and enables the 3GPP AAA Server to find the address of the HSS which holds the subscriber data for a given subscriber identity in a configuration with multiple, separately addressable HSSs.
The Home Location Register contains the primary subscriber database in networks that do not satisfy Release 6 of the IMS.
The Home Subscriber Server is an IMS function located within the 3GPP subscriber's home network. It contains a subscriber and authentication credential database required for the 3GPP subscriber to access the WLAN interworking service. The primary profile data used for policy decisions is downloaded from the HSS to the 3GPP AAA Server.
Offline Charging System
The WLAN AN periodically forwards collected offline charging information to the 3GPP AAA Server, which in turn forwards this information to the Offline Charging System. The offline charging system is located in either the VPLMN or HPLMN.
It is the CDF that has the responsibility of integrating many of these charging events into Charging Data Records (CDRs) and forwarding them to the Charging System.
The section describes the reference points associated with the 3GPP WLAN reference model network elements.
Reference point between a 3GPP AAA Server and an SLF. Used to enable the 3GPP AAA Server to find the address of the HSS which holds the subscriber data for a given subscriber identity in a configuration with multiple, separately addressable HSS's.
Reference point between a WLAN Access Network and a 3GPP AAA Server/Proxy (charging and control signalling). Used to transport authentication, authorization, and charging-related information. Protocol should be Diameter or RADIUS based.
Reference point between a 3GPP AAA Proxy and a 3GPP AAA Server (charging and control signalling). Applies to roaming cases only. Used to transport authentication, authorization, and related information in a secure manner.
Reference point between an Offline Charging System and a 3GPP AAA Server/Proxy. Used to transport/forward offline charging information towards the 3GPP operator's offline charging system located in the visited network or home network where the subscriber is residing.
Reference point between a PDG and a 3GPP AAA Server or 3GPP AAA Proxy. Used to retrieve tunneling attributes and authentication data for the purpose of tunnel establishment, tunnel data authentication, and encryption.
* Reference point is outside the scope of this document.
Figure 1 through Figure 3 present the 3GPP WLAN reference model in various service scenarios (roaming and non-roaming) along with the associated network elements and reference points.
Figure 1 shows a subscriber, represented by the WLAN UE, in a "non-roaming" scenario, meaning that the network elements in their home network are processing their requests. In this scenario, an authorized subscriber can access local IP networks such as the Internet or Intranet directly from the WLAN AN, or can access IMS services over the Wi reference point. The Juniper Networks IMS AAA Server is represented by the 3GPP AAA Server, and is responsible for performing the AAA functions within the network.
Figure 2 shows a subscriber, represented by the WLAN UE, in a "roaming" scenario, meaning that the subscriber has roamed outside their home network and is accessing a visited 3GPP network. In this scenario, the subscriber is accessing IMS services over the Wi reference point in their home network. The Juniper Networks IMS AAA Server is represented by the 3GPP AAA Server in either the visited or home 3GPP network.
Figure 3 shows a subscriber, represented by the WLAN UE, in a "roaming" scenario, meaning that the subscriber has roamed outside their home network and is accessing a visited 3GPP network. In this scenario, the subscriber is accessing IMS services over the Wi reference point in the visited network. The Juniper Networks IMS AAA Server is represented by the 3GPP AAA Server in either the visited or home 3GPP network.
NOTE: The IMS AAA Server performs the AAA functions of the 3GPP AAA Server/Proxy referenced in 3GPP TS 23.234: "3GPP System to Wireless Local Area Network (WLAN) Interworking; System description." Some of the network elements and reference points shown in the figures are not described here in detail because they are outside the scope of this document and application, or because they are not supported by the IMS AAA Server. The purpose of including these items is to show how the IMS AAA Server (3GPP AAA Server/Proxy) fits into the overall 3GPP WLAN Interworking architecture.