The present invention relates to interworking of wireless local area networks (WLANs) with cellular networks in order to provide connectivity for packet data services for cellular networks, particularly GSM-based cellular networks. The invention also relates to techniques to overlay security and privacy onto network elements that do not provide such.
There is a need for a solution that provides high-speed wireless data networking for a customer of GSM services. It is desirable to do so without modifying the core network elements of any GSM service and particularly those that have already deployed support for GSM Packet Radio Services (GPRS). By leaving the core network intact, it is believed that the cost of adding high-speed wireless data networking to a GSM network can be reduced.
Add-on high-speed wireless services must be provided as efficiently and inexpesively as possible in order to compete with integrated services. A first step towards achieving this goal would be to use standard-based networking elements, such as, but not limited to, WLAN devices using the IEEE 802.11b networking protocols. However, these networking protocols are relatively rudimentary and provide specifications merely for the first two layers of a typical Open Systems Interconnection (OSI) defined seven-layer stack: The physical layer and the Media Access and Control (MAC) layer.
FIG. 1 illustrates the conventional OSI model applied to an IEEE 802.11 and Internet Engineering Task Force (IETF) stack for a wireless LAN. In the past, in order to interconnect this stack to the GSM stack at the top or application level, application gateways had to be provided. This interface methodology for interoperation with WLAN systems is difficult for GSM/GPRS services to provide because GSM/GPRS services are based on completely different standards and provide many features not found in the IETF and IEEE 802.11b stacks. For instance, IETF systems do not yet provide the functionality needed to support GSM services. IETF protocols do not provide a secure authentication system for interoperation with the GSM authentication system, accounting functions are in different formats, allocation of customer IP addresses is handled at a different layer of the networking stacks, roaming features are incompatible, and the IETF does not specify a micro-mobility handover protocol such as that which is detailed in GSM. In fact, when interoperating IETF and GSM systems, the typical GSM service would simply deploy two separate systems and consolidate billing afterwards. This solution is undesirable, because it is difficult for the GSM operator to manage two disparate customer databases, provide two different servers and clients for each additional service they wish to deploy, and manage two entirely different network systems with different network management systems.
Therefore, there is a need for a set of interworking network elements that either translates services or provides additional services over the WLAN radio access network. In addition, there is a need to provide an architecture for interworking elements in a manner that requires little or no modifications to the GSM system.
There have been various efforts to address and improve the deployment of high-speed data services using WLAN. One such method provided by several vendors uses interworking elements between the WLAN and typical Internet Service Provider (ISP) core networks. In this method, WLAN Access Points (APs) providing physical layer and MAC layer functionality are connected to modified Internet Protocol (IP) routers. These routers typically support routing layer IETF standards such as, but not limited to, Routing Internet Protocol (RIP), and they typically use IETF standards-based authentication and accounting systems that incorporate protocols such as, but not limited to, Remote Access Dial In User Service (RADIUS).
Realizing these difficulties, several vendors (Cisco Systems of Santa Clara, Calif., Service Factory of Stockholm, Sweden, and Lucent Technologies) have tried to provide interworking elements in order to handle each of the above-described faults and many additional problems. For instance, several vendors have added features to the Access Points in order to add higher networking layer functionality such as authentication and security. This method is not ideal, because there is no IETF standard covering this area at this time. As such, using customized Access Points requires a GSM/GPRS service to deploy only those APs that are able to support these proprietary protocols. In addition, some vendors that have built additional features and functionalities into their WLAN client hardware have limited the type of network interface cards that customers can use to connect into the network and thus causes additional incompatibilities, which is particularly undesirable if the customer does not have the option of using a customized interface.
Realizing this difficulty, some vendors (Nokia of Finland, Cisco Systems, IP Unplugged of Sweden, PC Tel of Santa Clara, Calif.) have concentrated on providing back-end solutions to the billing and provisioning systems by adding so-called Charging Gateways. These gateways translate the billing records coming out of the standard IETF systems into the proprietary systems used by the GSM/GPRS services. Since there are no standards for billing systems, it is difficult to ensure transparency for new and future modifications to existing services.
Other vendors (Transat of Houston, Tex. and Interwave of Menlo Park, Calif.), recognizing these difficulties, have built stand-alone GSM/GPRS systems that communicate with customers using WLAN facilities, thereby replacing all of the core network functions and capabilities that exist in the GSM/GPRS core network. This system is also not desirable because the GSM/GPRS service must nonetheless continue to operate two distinct networks with different management and configuration commands and additional hardware and software, even though it provides the GSM operator with a more familiar replacement network.
Therefore, there is a need for an interworking system between the WLAN radio access network and the GSM/GPRS core network that enables the GSM service to transparently connect users over this new radio access network, while providing to GSM customers all of the services that the customers have come to expect. In addition, it would be useful if this interworking system could be extended in order to support other radio access networks such as 3G, 802.11a, or HIgh PErformance Radio Local Area Networks (HIPERLAN) in the future with little or no additional modification. Such a system would eschew any requirements for the WLAN elements to be modified and would interconnect the two networks at the lowest networking layers possible, as well as provide additional features at the lowest networking layers possible in order to make best possible use of the GSM standards already deployed. These features should be provided via separate networking elements. In this way, functionality can be added to other radio access networks with little additional work.
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