Inter-working function for the authentication of a terminal in a wireless local area network

BACKGROUND

Field

0001The present invention relates to an inter-working function for a communication system, and more specifically to mechanisms for common authentication and key exchange through an inter-working function for use in a Wireless Local Area Network (WLAN).

Background

0002A Wireless Local Area Network (WLAN) allows users virtually unrestricted access to Internet Protocol (IP) services and data networks. The use of a WLAN is not limited to laptop computers and other computing devices, but is rapidly expanding to include cellular telephones, Personal Digital Assistants (PDA)s, and other small wireless devices supported by an external network or carrier. For example, a wireless device communicating via a cellular carrier may roam into a WLAN in a cyber-cafe or work space. In this situation, the wireless device has access to the cellular system, but desires access to the WLAN. The WLAN access requires authentication. As the wireless device has already gained access to the cellular system, the need for further authentication is redundant. There is a need therefore, for an inter-working function that allows a common authentication for access to a cellular system and to a WLAN. Attention is drawn to the document <patcit id="pcit0001" dnum="US6128389A"><text>US 6 128 389 A</text></patcit>, which discloses a secure authentication center (SAC) that can be coupled to secure authentication key management systems (SAMS) of various communication system providers. In an example of the authentication process for mobile stations served by IS-41 based systems using the Cellular Authentication and Voice Encryption CAVE algorithm, a serving system transmits a global challenge indicator and a random number to the mobile station. In response, the mobile station generates an authentication signal. The serving system sends the authentication signal to the SAC. If the SAC does not have shared secret data (SSD), or wants to update the SSD, the SAC transmits a request to the SAMS. Attention is also drawn to the article "<nplcit id="ncit0001" npl-type="s"><text>Wireless LAN Access Architecture for Mobile Operators: Ala-Laurila, J. et al. IEEE Communication Magazine, pages 82 to 89, November 2001</text></nplcit>; IEEE Service Centre, Piscataway, N.J, US. The article describes a LAN system architecture that combines WLAN radio access technology with mobile operator SIM based subscriber management functions and roaming infrastructures. In the disclosed system WLAN access is authenticated and charged using GSM SIM. In accordance with the present invention a method and apparatus, as set forth in claims 1 and 3 are provided. Embodiments of the invention are claimed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

0003<figref idref="f0001">FIG.1</figref> is communication system including a Wireless Local Area Network (WLAN).

0004<figref idref="f0002">FIG. 2</figref> is a communication system having an Inter-working Function (IWF) unit.

0005<figref idref="f0003">FIG. 3</figref> is a timing diagram of an authentication process in a communication system

0006<figref idref="f0004">FIG. 4</figref> is a flow diagram of an authentication process.

0007<figref idref="f0005">FIG. 5</figref> is a timing diagram of an authentication process in a communication system.

0008<figref idref="f0006">FIG. 6</figref> is a flow diagram of an authentication process at an IWF in a communication system.

0009<figref idref="f0007">FIG. 7</figref> is a flow diagram of authentication processing at a mobile station.

DETAILED DESCRIPTION

0010The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments

0011An HDR subscriber station, referred to herein as an access terminal (AT), may be mobile or stationary, and may communicate with one or more HDR base stations, referred to herein as modem pool transceivers (MPTs). An access terminal transmits and receives data packets through one or more modem pool transceivers to an HDR base station controller, referred to herein as a modem pool controller (MPC). Modem pool transceivers and modem pool controllers are parts of a network called an access network. An access network transports data packets between multiple access terminals. The access network may be further connected to additional networks outside the access network, such as a corporate intranet or the Internet, and may transport data packets between each access terminal and such outside networks. An access terminal that has established an active traffic channel connection with one or more modem pool transceivers is called an active access terminal, and is said to be in a traffic state. An access terminal that is in the process of establishing an active traffic channel connection with one or more modem pool transceivers is said to be in a connection setup state. An access terminal may be any data device that communicates through a wireless channel or through a wired channel, for example using fiber optic or coaxial cables. An access terminal may further be any of a number of types of devices including but not limited to PC card, compact flash, external or internal modem, or wireless or wireline phone. The communication link through which the access terminal sends signals to the modem pool transceiver is called a reverse link. The communication link through which a modem pool transceiver sends signals to an access terminal is called a forward link.

0012A Wireless Local Area Network (WLAN) 100 is illustrated in <figref idref="f0001">FIG. 1</figref> having multiple Access Points (APs) 106, 108, 110. An AP is a hub or bridge that provides a star topology control of the wireless side of the WLAN 100, as well as access to the wired network.

0013Each AP 106, 108, 110, as well as others not shown, supports a connection to a data service, such as the Internet. A workstation 102, such as a laptop computer, or other digital computing device, communicates with an AP via the air interface, thus the term Wireless LAN. The AP then communicates with an Authentication Server (AS) or Authentication Center (AC). The AC is a component for performing authentication services for devices requesting admittance to a network. Implementations include Remote Authentication Dial-In User Service (RADIUS), which is an Internet user authentication described in RFC 2138, "Remote Authentication Dial In User Service (RADIUS)" by C. Rigney et al., published April 1997, and other Authentication, Authorization and Accounting (AAA) servers.

0014Wireless networking is emerging as a significant aspect of internetworking. It presents a set of unique issues based on the fact that the only boundary of a wireless network is the radio signal strength. There is no wiring to define membership in a network. There is no physical method to restrict a system within radio range to be a member of a wireless network. Wireless networking, more than any other networking technology, needs an authentication and access control mechanism. Various groups are currently working on developing a standard authentication mechanism. Currently the accepted standard is the IEEE 802.11.

0015The nature of an RF based network leaves it open to packet interception by any radio within range of a transmitter. Interception can occur far outside the users 'working' range by using hi-gain antennas. With readily available tools, the eavesdropper is not limited to just collecting packets for later analysis, but can actually see interactive sessions like web pages viewed by a valid wireless user. An eavesdropper can also catch weak authentication exchanges, like some website logins. The eavesdropper could later duplicate the logon and gain access.

0016Once an attacker has gained the knowledge of how a WLAN controls admittance, he may be able to either gain admittance to the network on his own, or steal a valid user's access. Stealing a user's access is simple if the attacker can mimic the valid user's MAC address and use its assigned IP address. The attacker waits until the valid system stops using the network and then takes over its position in the network. This would allow an attacker direct access to all devices within a network, or to use the network to gain access to the wider Internet, all the while appearing to be a valid user of the attacked network. Therefore, authentication and encryption become key concerns in implementation of a WLAN.

0017Authentication is the process of proving the identity of an individual or application in a communication. Such identification allows the service provider to verify the entity as a valid user and also to verify the user for the specific services requested. Authentication and authorization actually have very specific meanings, though the two names are often used interchangeably, and in practice are often not clearly distinguished.

0018Authentication is the process where a user establishes a right to an identity -- in essence, the right to use a name. There are a large number of techniques that may be used to authenticate a user -- passwords, biometric techniques, smart cards, certificates.

0019A name or identity has attributes associated with it. Attributes may be bound closely to a name (for example, in a certificate payload) or they may be stored in a directory or other database under a key corresponding to the name. Attributes may change over time.

0020Authorization is the process of determining whether an identity (plus a set of attributes associated with that identity) is permitted to perform some action, such as accessing a resource. Note that permission to perform an action does not guarantee that the action can be performed. Note that authentication and authorization decisions can be made at different points, by different entities.

0021In a cellular network, the authentication feature is a network capability that allows cellular networks to validate the identity of wireless device, thereby reducing unauthorized use of cellular networks. The process is transparent to subscribers. Customers are not required to do anything to authenticate the identity of their phones when they make a call.

0022Authentication typically involves a cryptographic scheme, wherein the service provider and the user have some shared information and some private information. The shared information is typically referred to as a "shared secret."

The A-Key

0023The authentication key (A-key) is a secret value that is unique to each individual cellular phone. It is registered with the cellular service provider and stored in the phone and Authentication Center (AC). The A-key is programmed into the phone by the manufacturer. It can also be entered manually by the user, from the wireless device menu, or by a special terminal at the point of sale.

0024The wireless device and the AC must have the same A-key to produce the same calculations. The primary function of the A-key is to be used as a parameter to calculate the shared secret data (SSD).

The Shared Secret Data (SSD)

0025The SSD is used as an input for authentication calculations in the wireless device and the AC, and is stored in both places. Unlike the A-key, the SSD may be modified over the network. The AC and the wireless device share three elements that go into the calculation of the SSD: 1) the Electronic Serial Number (ESN); 2) the Authentication Key (A-Key); and 3) a RANDom number for Shared Secret Data calculation (RANDSSD).

0026The ESN and RANDSSD are transmitted over the network and over the air interface. The SSD is updated when a device makes its first system access, and periodically thereafter. When the SSD is calculated, the result is two separate values, SSD-A and SSD-B. SSD-A is used for authentication. SSD-B is used for encryption and voice privacy.

0027Depending on the capabilities of the serving system, SSD may be shared or not shared between the AC and serving Mobile Switching Center (MSC). If secret data is shared, it means the AC will send it to the serving MSC and the serving MSC must be capable of executing CAVE. If it is not shared, the AC will keep the data and perform authentication.

0028The type of sharing affects how an authentication challenge is conducted. An authentication challenge is a message sent to challenge the identify of the wireless device. Basically, the authentication challenge sends some information, typically random number data, for the user to process. The user then processes the information and sends a response. The response is analyzed for verification of the user. With shared secret data, a challenge is handled at the serving MSC. With non-shared secret data, a challenge is handled by the AC. By sharing secret data, the system may minimize the amount of traffic sent and allow challenges to happen more quickly at the serving switch.

Authentication Procedures

0029In a given system, a Home Location Register (HLR) controls the authentication process by acting as intermediary between the MSC and AC. The serving MSC is set up to support authentication with the mobile's HLR and vice versa.

0030The device initiates the process by notifying the serving MSC if it is capable of authentication, by setting an authorization field in the overhead message train. In response, the serving MSC starts the registration/authentication process with an Authentication Request.

0031By sending the Authentication Request, the serving MSC tells the HLR/AC whether it is capable of doing CAVE calculations. The AC controls which of the serving MSC's as well as device capabilities will be used out of those available. When the serving MSC does not have CAVE capability, the SSD cannot be shared between the AC and MSC and therefore all authentication processes are performed in the AC.

0032The purpose of the Authentication Request (AUTHREQ) is to authenticate the phone and request SSD. The AUTHREQ contains two parameters for authentication, the AUTHR and RAND parameters. When the AC gets the AUTHREQ, it uses the RAND and the last known SSD to calculate AUTHR. If it matches the AUTHR sent in the AUTHREQ then authentication is successful. The return result to the AUTHREQ will contain the SSD if it can be shared.

The Challenge

0033The Authentication process consists of a challenge and response dialog. If SSD is shared, the dialog runs between the MSC and the device. If SSD is not shared, the dialog runs between the HLR/AC and the device. Depending on the switch type, the MSC may be capable of either a Unique Challenge, a Global Challenge, or both. Some MSCs are currently not capable of global challenge. The Unique Challenge is a challenge that occurs during call attempts only, because it uses the voice channel. Unique challenge presents an authentication to a single device during call origination and call delivery. The Global Challenge is a challenge that occurs during registration, call origination, and call delivery. The Global challenge presents an authentication challenge to all MSs that are using a particular radio control channel. It is called global challenge because it is broadcast on the radio control channel, and the challenge is used by all phones accessing that control channel.

0034During a challenge, the device responds to a random number provided by the MSC or AC. The device uses the random number and shared secret data stored in the device to calculate a response to the MSC. The MSC also uses the random number and shared secret data to calculate what the response from the device should be. These calculations are done through the CAVE algorithm. If the responses are not the same, service is denied. The challenge process does not increase the amount of time it takes to connect the call. In fact, the call may proceed in some cases, only to be torn down when authentication fails.

0035Wireless Local Area Networks (WLANs) have gained tremendous popularity as a means of providing users with untethered access to IP data networks. Third-generation (3G) wireless networks are also designed to offer high-speed data access; although the data rates they support are typically lower than those of WLANs, 3G networks offer data coverage over a much wider area. Though they might be viewed as competitors, WLAN and 3G networks may be complementary: WLANs offer high-capacity "hot-spot" coverage in public areas such as airport lounges and hotel lobbies, while 3G networks can provide users with nearly ubiquitous data service while on the move. Therefore, the same carrier may provide both 3G and WLAN access services under a single user subscription. This means that the MS uses the same authentication method and secret to both types of access authentication.

0036In 3G access authentication, the Authentication Center (AC) authenticates the MS. The AC and the MS have a shared secret. On the network side, the shared secret is securely stored in the AC and is not distributed to any other network entities. On the MS side, the shared secret is securely stored in the secured memory and is not distributed outside of it. The AC and MS use either the Cellular Authentication Voice Encryption (CAVE) or Authentication Key Agreement (AKA) as the authentication algorithm. The authentication parameters are delivered between the MS and AC via 3G over-the-air signaling messages and network signaling messages (e.g., IS-41).

0037In WLAN access authentication, it is desirable that the MS is authenticated by the same AC using the same shared secret and authentication algorithm (AKA or CAVE). However, different mechanisms are used to deliver the authentication parameters in WLAN. Specifically, the authentication parameters are delivered via the Extensible Authentication Protocol (EAP) and an AAA protocol (RADIUS or Diameter). The challenge is to interwork the delivery mechanisms between 3G and WLAN so that the authentication parameters can be delivered between the MS and AC for WLAN access authentication.

0038As stated hereinabove, the CAVE algorithm is commonly used for cellular communications and therefore, is well used and distributed. Alternate algorithms for authentication are also used. Specifically in data communications a variety of algorithms exist of varying complexity and application. To coordinate these mechanisms, the Extensible Authentication Protocol (EAP) has been developed as a general protocol framework that supports multiple authentication and key distribution mechanisms. The EAP is described in "<nplcit id="ncit0002" npl-type="b"><text>PPP Extensible Authentication Protocol (EAP)" by L. Blunk et al., RFC 2284, published March 1998</text></nplcit>.

0039One such mechanism supported by the EAP as defined in "<nplcit id="ncit0003" npl-type="b"><text>EAP AKA Authentication" by J. Arkko et al., published as an Internet Draft in February 2002</text></nplcit>, is the AKA algorithm. There is a need therefore to extend EAP to include the cellular algorithm CAVE. This is desirable to provide back compatibility for new systems and networks.

EAP

0040The Extensible Authentication Protocol (EAP) is a general protocol for authentication which supports multiple authentication mechanisms. EAP does not select a specific authentication mechanism during link set up and control, but rather postpones this until the authentication procedure begins. This allows the authenticator to request more information before determining the specific authentication mechanism. The authenticator is defined as the end of the link requiring the authentication. The authenticator specifies the authentication protocol to be used in the during link establishment.

Inter-Working Function (IWF)

0041According to one embodiment, a new network entity is implemented and referred to as the Inter-Working Function (IWF) or more specifically, the AAA/IS-41 InterWorking Function (IWF). The IWF interworks the delivery mechanisms of authentication parameters (e.g., CAVE, AKA) between wireless networks, such as 3G, and WLAN networks. An IWF 204 is illustrated in <figref idref="f0002">FIG. 2</figref> as part of a communication system 200. The system 200 includes a WLAN 202, an IWF 204 and an AC 206. As illustrated, a workstation 208 is currently within the communication range of the WLAN 202. The IWF 204 provides an interface between AC 206 and WLAN 202, allowing the use of a common authentication to allow MS 208 to gain access to the network. Note that the MS 208 may be a wireless workstation, a remote user, or other wireless device that is capable of communicating via a network other than the WLAN 202, which in this case is the network of which AC 206 is a part.

0042The IWF 204 is a one-way interworking function, i.e., the authentication request is originated from the WLAN 202. Note that in the current embodiment and illustration, AAA is the delivery mechanism for transporting authentication parameters between WLAN 202 and IWF 204. Further, IS-41 is the delivery mechanism for transporting authentication parameters between IWF 204 and AC 206. Specific to this example, RADIUS will be used as the AAA protocol.

0043Authentication processing is illustrated in <figref idref="f0003">FIG. 3</figref>. Initially, the IWF 204 receives a RADIUS Access-Request message that contains the identity of the MS 208 (or wireless workstation) that wants to perform the authentication for access to the WLAN 202. The IWF 204 is configured with a database 210 storing the authentication capability associated with the MS 208, as well as other MS 208 currently registered via the AC 206. The database 210 is indexed by each MS 208 identity. Thus, the IWF 204 may determine the MS 208 authentication capability (e.g., AKA and/or CAVE).

0044If the MS 208 only supports CAVE, the IWF 204 performs the following procedure consistent with <figref idref="f0003">FIG. 3</figref>. The IWF sends a RADIUS Access-Challenge message that contains an EAP Request message containing a CAVE Challenge. As discussed hereinabove, the challenge contains a random number to be used by the MS 208 for computing an authentication response. The IWF 204 receives the RADIUS Access-Request message containing the EAP Response message (containing the CAVE Challenge Response). The CAVE response contains the MS 208 authentication response, i.e., the result of computations using the random number, and other parameters specific to the MS 208.

0045If the IWF 204 is not capable of verifying the EAP Response message, or specifically is not capable of verifying the CAVE response to the CAVE challenge, the IWF 204 sends an AUTHREQ message, which is an IS-41 message, to the AC 206. In this case, the IWF 204 does not have the information necessary to confirm the challenge response. The AUTHREQ message contains the IMSI assigned to the MS 208, the random number (i.e., the challenge), and the authentication response produced by the MS 208. The AC 206, which has knowledge of the shared secret specific to the MS 208, then verifies the MS 208 challenge response. The AC 206 returns the AUTHREQ message, which is an IS-41 message, to the IWF. The AUTHREQ message contains the authentication outcome. If successful, the AUTHREQ message also contains a key called the Cellular Message Encryption Algorithm (CMEA) key, which is used for protecting the MS 208 traffic in the WLAN 202. If the IWF 204 is unable to receive the AUTHREQ message from the AC 206 after a predetermined number of retries, the IWF 204 sends the RADIUS Access-Reject message containing the EAP-Failure to the WLAN 202. The inability to receive an AUTHREQ message may indicate network problems between the IWF 204 and AC 206.

0046If the IWF 204 is capable of verifying the challenge response from the MS 208, and such verification is successful, the IWF 204 generates the CMEA key. If the MS 208 is authenticated successfully, the IWF 204 sends a RADIUS Access-Accept message to the WLAN 202. Such message containing an EAP-Success message as well as the CMEA key. If the MS 208 fails the authentication, the IWF 204 sends a RADIUS Access-Reject message containing an EAP-Failure message to the WLAN 202.

0047<figref idref="f0004">FIG. 4</figref> illustrates an authentication process 400 according to one embodiment, wherein the MS 208 supports the CAVE protocol. The process starts when the MS 208 and the WLAN 202 begin identification negotiations at step 402. Also at this step, the WLAN 202 sends a RADIUS Access Request message containing the identity of the MS 208. As indicated hereinabove, the identity may be provided by way of the IMSI or other unique identifier for the MS 202. The process involves the MS 208 seeking access to the WLAN 202 and in response, the WLAN 202 requesting identification from the MS 208, step 402. At this point, the IWF 204 sends a RADIUS access challenge message to the WLAN 202, containing the CAVE challenge at step 404. In response to the challenge, the MS 208 computes a response and provides the response to the WLAN 208 (not shown). The response is then sent to the IWF 204 in a RADIUS access response message at step 406. If the IW F 204 does not have knowledge of the shared secret for the MS 208 at decision diamond 408, processing continues to step 410 wherein the IWF 204 sends an AUTHREQ message to AC 206. The AUTHREQ message requests authentication of the MS 208. If an AUTHREQ message is returned at decision diamond 412, processing continues to decision diamond 414 to determine if the AUTHREQ message indicates successful authentication, i.e., result of authentication is approval for access to the WLAN. If the AUTHREQ message is not received at decision diamond 412, processing continues to step 416, wherein the IWF sends a RADIUS access reject message.

0048Continuing from decision diamond 408, if the IWF 204 has knowledge of the MS 208 shared secret information, the IWF 204 is able to determine if authentication is successful at decision diamond 418. Successful authentication proceeds to step 420 to compute the CMEA key. A RADIUS access accept message is then sent at step 424. Note that successful authentication at step 414 (for authentication by the AC 206) also proceeds to step 420. From decision diamond 418, if the authentication is not successful, the IWF sends a RADIUS access reject message at step 422.

0049In an alternate embodiment, the IWF 204 uses the AKA protocol for sending a challenge. As illustrated in <figref idref="f0005">FIG. 5</figref>, if the MS 208 supports AKA, the IWF 204 implements the AKA challenge, and the order of authentication processing is changed. In this scenario, the information sufficient to authenticate a user, such as MS 208, is provided in an Authentication Vector (AV). Note that the AC 206 may send the Shared Secret (SS) information in the AV to the IWF 204. According to the present embodiment, the AV includes the SS, the challenge and a Cipher Key (CK). The CK is used for encrypting MS traffic.

0050If the IWF 204 does not have the Authentication Vector (AV) to authenticate the MS 208, the IWF 204 sends an AUTHREQ message to request the AV from the AC 206. The AUTHREQ message contains the identify of the MS 208, such as the IMSI, and the request for the AV. The AC 206 replies with the AUTHREQ message that contains the AV. The AV consists of a random number (RAND), an expected response (XRES), a Cipher Key (CK), and an authentication token (AUTN). The AC may provide multiple AVs in the AUTHREQ message, so the IWF doesn't need to request from the AC 206 subsequent authentication.

0051If the IWF 204 is unable to receive the AUTHREQ message from the AC 206 (which may be after some predetermined number of retries), the IWF 204 sends a RADIUS Access Reject message containing an EAP-Failure message to the WLAN 202, such as when there are network problems between the IWF 204 and the AC 206.

0052If the received AUTHREQ does not contain the AV, the IWF 204 sends the RADIUS Access-Reject message containing the EAP-Failure message to the WLAN 202. For example, such a case may present when the MS 202 has an expired subscription.

0053If the IWF 204 has the AV, the IWF 204 sends a RADIUS Access-Challenge message containing an EAP-Request message having an AKA-Challenge to the WLAN 202. The AKA challenge contains the AUTN and the RAND. The AUTN conveys the AC 206 credentials and will be verified by the MS 208. The RAND is a challenge to the MS 208 that is used to compute an authentication response (RES). The MS 208 provides the RES to the WLAN 202.

0054The IWF 204 receives the RADIUS Access-Request message containing an EAP-Response including a CAVE-Challenge from the WLAN 202. The CAVE challenge contains the MS 208 authentication response (RES) received via the WLAN 202. The IWF 204 compares the RES with XRES. For a match, the MS 208 is authenticated successfully, and the IWF 204 sends a RADIUS Access-Accept message to the WLAN 202. Such message contains an EAP-Success message and a CK. The CK will be used for protecting the MS 208 traffic in WLAN 202. If the MS 208 fails the authentication, the IWF 204 sends a RADIUS Access-Reject message containing an EAP-Failure message to the WLAN 202.

0055<figref idref="f0006">FIG. 6</figref> illustrates an authentication procedure 500 using the AV. If the IWF 204 has the AV to sufficient to verify MS 208 at decision diamond 502, the process continues to step 506, else processing continues to step 504. At step 506 the IWF 204 sends a RADIUS access challenge message to the WLAN 202 for MS 208. The challenge is then forwarded to the MS 208 for processing, and a response is provided back to the WLAN 202 (not shown). The IWF 204 receives the RADIUS access request message at step 510, and determines if the MS authentication is successful at decision diamond 512. On a successful authentication, the IWF 204 sends a Radius access accept message at step 514, else the IWF 204 sends a RADIUS access reject message at step 516.

0056Returning to decision diamond 502, if the IWF 204 does not have the AV, the IWF sends an AUTHREQU message to AC 206 at step 504. On receipt of the AV, the IWF 204 continues processing to step 506, else processing continues to step 516.

0057<figref idref="f0007">FIG. 7</figref> illustrates an IWF 600 adapted to interface between a WLAN (not shown), and therefore capable of performing the procedures necessary for communication, authentication, key exchange, and other security communications therewith, and an AC (not shown), and therefore capable of performing the procedures necessary for communication, authentication, key exchange, and other security communications therewith. The IWF 600 includes a WLAN interface unit 602, which prepares, transmits, receives and/or interprets communications with a WLAN. Similarly, IWF 600 includes an AC interface unit 604, which prepares, transmits, receives, and/or interprets communications with an AC. The IWF 600 further includes a CAVE procedure unit 608, an EAP procedure unit 610, and a RADIUS procedure unit 612. The IWF 600 may include any number of such procedure units (not shown) as required for inter-working function in a given system. The procedure units, such as CAVE procedure unit 608, EAP procedure 610 and RADIUS procedure 612, may be implemented in software, hardware, firmware, or a combination thereof. The various modules within IWF 600 communicate via communication bus 614.

0058Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

0059Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

0060The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

0061The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

0062The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled, in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the invention, as defined by the following claims.