Abstract:
Methods and apparatus are presented herein for allowing a wireless communication device to perform a proxy authentication on behalf of a tethered device and ensure the authentication is encrypted.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is a continuation-in-part of U.S. patent application Ser. No. 10/627,171 filed Jul. 25, 2003, which published as U.S. Patent Application No. 2005/0039005 on Feb. 17, 2005 and will issue as U.S. Pat. No. 7,239,865 on Jul. 3, 2007, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     1. Field  
         [0003]     The present invention relates generally to wireless communication networks and packet switched data networks. More specifically, the present invention relates to using a wireless communication device to perform a proxy authentication on behalf of a tethered device, wherein the tethered device is using the wireless communication network to access a packet switched data network.  
         [0004]     2. Background  
         [0005]     The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for remote subscribers. As used herein, the term “cellular” system encompasses systems using either cellular or personal communications services (PCS) frequencies. Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high-data-rate systems are promulgated by the Telecommunication Industry Association (TIA) and other well-known standards bodies.  
         [0006]     Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assigned to the assignee of the present invention and incorporated by reference herein. An exemplary system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate Submission (referred to herein as cdma2000), issued by the TIA. The standard for cdma2000 is given in the draft versions of IS-2000 (cdma2000 1.times.EV-DV) and IS-856 (cdma2000 1.times.EV-DO) and has been approved by the TIA. Another CDMA standard is the W-CDMA standard, as embodied in 3rd Generation Partnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214. The W-CDMA standard is in the process of incorporation into a GSM-based system known as Universal Mobile Telecommunications Systems (UMTS).  
         [0007]     The telecommunication standards cited above are examples of only some of the various communications systems that can be implemented. One general category of standards is referred to as “Third Generation” or “3G,” of which cdma2000 and W-CDMA are both members. These  3 G standards are directed towards increased data rates, which will support increased user numbers and data-intensive applications.  
         [0008]     Given the growing demand for wireless data applications, the need for very efficient wireless data communication systems has become increasingly significant. One such wireless data application is the transmission of data packets that originate or terminate at packet-switching networks. Various protocols exist for transmitting packetized traffic over packet-switching networks so that information arrives at its intended destination. The primary protocol for transmitting packetized traffic is “The Internet Protocol,”, Request for Comment (RFC) 791 (September, 1981). The Internet Protocol (IP) breaks up messages into packets, routes the packets from a sender to a destination, and reassembles the packets into the original messages at the destination. The IP protocol requires that each data packet begins with an IP header containing source and destination address fields that uniquely identifies host and destination computers. Another protocol is the Point-to-Point Protocol (PPP), promulgated in RFC 1661 (July 1994), which is an encapsulation protocol for transporting IP traffic over point-to-point links. Yet another protocol is the IP Mobility Support, promulgated in RFC. 2002 (October 1996), which is a protocol that provides for transparent outing of IP datagrams to mobile nodes.  
         [0009]     Hence, the transmission of IP packets from the IP network over a wireless communication network or from the wireless communication network over the IP network can be accomplished by adherence to a set of protocols, referred to as a protocol stack. A wireless communication device may be the origination or the destination of the IP packet, or alternatively, the wireless communication device may be a transparent link to an electronic device. In either case, payload information is broken into packets wherein header information is added to each packet. The IP header sits on top of the PPP layer, which sits on the RLP layer, which sits on top of the physical layer of the wireless air interface. The RLP layer is the Radio Link Protocol layer, which is responsible for selectively retransmitting packets when a transmission error occurs. In a WCDMA system, the PPP layer sits on the Radio Link Control (RLC) layer, which has a similar functionality as the RLP layer.  
         [0010]     Data may be transported over-the-air to a packet data service node (PDSN) via an Access Point (AP), whereupon the data is subsequently sent over an IP network. Using terminology from cellular communication system, an AP may also be thought of as a base station or a base station equivalent. Alternatively, IP packets may be transmitted over an IP network to a PDSN, from a PDSN to an AP, and then over-the-air to a wireless communication device. A wireless communication device may be referred to as an Access Terminal (AT) in the terminology of a wireless communication protocol or alternatively, the wireless communication device may be referred to as a Mobile Node (MN) in the terminology of an IP protocol.  
         [0011]     There are numerous difficulties that abound when attempting to wirelessly transfer data that originates or terminates in wired environments. One such difficulty is the authentication of the devices that attempt to access packet data services via wireless communications equipment. Due to the multiplicity of protocols involved in transmitting IP packets over a wireless environment, there are a multiplicity of authentication procedures that must be satisfied if a device tethered to a wireless communication device desires access to a wired network. In one possible scenario, the wireless communication device would be required to satisfy authentication procedures of the wireless network, the tethered device may be required to satisfy authentication procedures of the wired network, and the authentication procedures of one may affect the authentication procedures of the other. Hence, when multiple protocols are used, the implementation of different authentication requirements corresponding to each protocol is possible within an end-to-end communication session. However, to implement different authentication requirements in a timely and computationally efficient fashion is problematic.  
       SUMMARY  
       [0012]     Methods and apparatus are presented herein to address the above stated difficulties. In an embodiment, a method is presented for performing an encrypted proxy authentication of a terminal equipment coupled to a wireless unit, the method including intercepting in the wireless unit a link control protocol message directed to the terminal equipment; determining if an authentication protocol indicated in the link control protocol message is acceptable to the wireless unit; and generating an appropriate response to the link control protocol message without input from the terminal equipment. In another embodiment, the generated response may indicate an acceptable authentication protocol. In another aspect, if a predetermined number of retries has expired, the generated response may reject authentication as a configuration option. In another embodiment, if the link control protocol message indicates an acceptable authentication protocol, the link control protocol message is forwarded to the terminal equipment. In another embodiment, if the link control protocol message includes an authentication challenge, the acceptable response is a response to the challenge, and the challenge is forwarded to the terminal equipment, while a challenge response received from the tethered device is ignored.  
         [0013]     In another embodiment, an apparatus within a wireless unit is presented for performing a proxy authentication of a terminal equipment coupled to the wireless unit, the apparatus comprising: at least one memory element; and at least one processing element configured to execute a set of instructions stored upon the at least one memory element, the set of instructions for: intercepting in the wireless unit a link control protocol message directed to the terminal equipment; determining if an authentication protocol indicated in the link control protocol message is acceptable to the wireless unit; and generating an appropriate response to the link control protocol message without input from the terminal equipment.  
         [0014]     In another embodiment, an apparatus is presented for performing a proxy authentication of a device tethered to a wireless unit, the apparatus including means for intercepting in the wireless unit a link control protocol message directed to the terminal equipment; means for determining if an authentication protocol indicated in the link control protocol message is acceptable to the wireless unit; and means for generating an appropriate response to the link control protocol message without input from the terminal equipment. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a diagram of a wireless communication network.  
         [0016]      FIG. 2  is a diagram of the data connectivity between an Access Terminal (AT), an Access Network (AN), an AN-Authentication, Authorization, and Accounting (AN-AAA) server, and a PDSN.  
         [0017]      FIG. 3  is an illustration of the program flow for a proxy authentication.  
         [0018]      FIG. 4  is a process flow diagram for a portion of a method of enforcing an encrypted proxy authentication.  
         [0019]      FIG. 5  is a process flow diagram for a portion of the processing of a mobile node that does not enforce encrypted proxy authentication.  
         [0020]      FIG. 6  is a process flow diagram for a portion of the processing of a mobile node of an embodiment that enforces encrypted proxy authentication.  
         [0021]      FIG. 7  is an illustration of the program flow for a successful proxy encrypted authentication negotiation according to the embodiment illustrated in  FIG. 6 .  
         [0022]      FIG. 8  is an illustration of the program flow for an unsuccessful proxy encrypted authentication negotiation according to the embodiment illustrated in  FIG. 6 .  
         [0023]      FIG. 9  is an illustration of an alternative program flow for an unsuccessful proxy encrypted authentication negotiation according to the embodiment illustrated in  FIG. 6 .  
         [0024]      FIG. 10  is a process flow diagram for a portion of the processing of a mobile node of an alternative embodiment that enforces encrypted proxy authentication.  
         [0025]      FIG. 11  is an illustration of the program flow for an unsuccessful proxy encrypted authentication negotiation according to the embodiment illustrated in  FIG. 10 .  
         [0026]      FIG. 12  is a diagram of a protocol stack of an embodiment.  
     
    
     DETAILED DESCRIPTION  
       [0027]     As illustrated in  FIG. 1 , a wireless communication network  10  generally includes a plurality of access terminals (also called remote stations, mobile stations, subscriber units, or user equipment)  12   a - 12   d , a plurality of base stations (also called base station transceivers (BTSs) or Node B).  14   a - 14   c , a base station controller (BSC) (also called radio network controller or packet control function  16 ), a mobile switching center (MSC) or switch  18 , a packet data serving node (PDSN) or internetworking function (IWF)  20 , a public switched telephone network (PSTN)  22  (typically a telephone company), and a packet switched data network  24  (typically an Internet Protocol (IP) network). For purposes of simplicity, four access terminals  12   a - 12   d , three base stations  14   a - 14   c , one BSC  16 , one MSC  18 , and one PDSN  20  are shown. It would be understood by those skilled in the art that there could be any number of access terminals  12 , base stations  14 , BSCs  16 , MSCs  18 , and PDSNs  20 .  
         [0028]     In one embodiment the wireless communication network  10  is a packet data services network. The access terminals  12   a - 12   d  may be any of a number of different types of wireless communication device such as a portable phone, a cellular telephone that is connected to a laptop computer running IP-based Web-browser applications, a cellular telephone with associated hands-free car kits, a personal data assistant (PDA) running IP-based Web-browser applications, a wireless communication module incorporated into a portable computer, or a fixed: location communication module such as might be found in a wireless local loop or meter reading system. In the most general embodiment, access terminals may be any type of communication unit.  
         [0029]     The access terminals  12   a - 12   d  may advantageously be configured to perform one or more wireless packet data protocols such as described in, for example, the EIA/TIA/IS-707 standard. In a particular embodiment, the access terminals  12   a - 12   d  generate IP packets destined for the IP network  24  and encapsulates the IP packets into frames using a point-to-point protocol (PPP).  
         [0030]     In one embodiment the IP network  24  is coupled to the PDSN  20 , the PDSN  20  is coupled to the MSC  18 , the MSC is coupled to the BSC  16  and the PSTN  22 , and the BSC  16  is coupled to the base stations  14   a - 14   c  via wirelines configured for transmission of voice and/or data packets in accordance with any of several known protocols including, e.g., E1, T1, Asynchronous Transfer Mode (ATM), Internet Protocol (IP), Point-to-Point Protocol (PPP), Frame Relay, High-bit-rate Digital Subscriber Line (HDSL), Asymmetric Digital Subscriber Line (ADSL), or other generic digital subscriber line equipment and services (xDSL). In an alternate embodiment, the BSC  16  is coupled directly to the PDSN  20 , and the MSC  18  is not coupled to the PDSN  20 .  
         [0031]     During typical operation of the wireless communication network  10 , the base stations  14   a - 14   c  receive and demodulate sets of reverse link signals from various access terminals  12   a - 12   d  engaged in telephone calls, Web browsing, or other data communications. Each reverse link signal received by a given base station  14   a - 14   c  is processed within that base station  14   a - 14   c . Each base station  14   a - 14   c  may communicate with a plurality of access terminals  12   a - 12   d  by modulating and transmitting sets of forward link signals to the access terminals  12   a - 12   d . For example, as shown in  FIG. 1 , the base station  14   a  communicates with first and second access terminals  12   a ,  12   b  simultaneously, and the base station  14   c  communicates with third and fourth access terminals  12   c ,  12   d  simultaneously. The resulting packets are forwarded to the BSC  16 , which provides call resource allocation and mobility management functionality including the orchestration of soft handoffs of a call for a particular access terminal  12   a - 12   d  from one base station  14   a - 14   c  to another base station  14   a - 14   c . For example, an access terminal  12   c  is communicating with two base stations  14   b ,  14   c  simultaneously. Eventually, when the access terminal  12   c  moves far enough away from one of the base stations  14   c , the call will be handed off to the other base station  14   b.    
         [0032]     If the transmission is a conventional telephone call, the BSC  16  will route the received data to the MSC  18 , which provides additional routing services for interface with the PSTN  22 . If the transmission is a packet-based transmission such as a data call destined for the IP network  24 , the MSC  18  will route the data packets to the PDSN  20 , which will send the packets to the IP network  24 . Alternatively, the BSC  16  will route the packets directly to the PDSN  20 , which sends the packets to the IP network  24 .  
         [0033]     In a WCDMA system, the terminology of the wireless communication system components differs, but the functionality is the same. For example, a base station can also be referred to as a Radio Network Controller (RNC) operating in a UMIS Terrestrial Radio Access Network (U-TRAN).  
         [0034]     In the various existing communication systems, different nomenclature exists for the various formats in which voice and data traffic can be transmitted, such as, e.g. frames, packets, and subpackets. The scope of the embodiments described herein extends to all wireless communication systems using any of the various transmission formats. However, for the purpose of illustrative ease, the term “packets” will be used herein to describe both the transmission channel format in which traffic is carried and the structure of the traffic.  
         [0035]     It should be noted that the “packets” of the CDMA system are structurally distinct from the IP “packets” of the packet switched data network. Both are units describing the format in which data is transmitted, but one is optimized for wireless networks and the other is optimized for a packet switched data network. For example, a data packet from an IP source would contain a header portion and a data portion. However, a data packet for transmission over-the-air carries data that has been encoded and modulated, and probably subjected to symbol repetition before being packed into a packet. Hence, a packet from a packet switched data network will have to be reformatted for use on the wireless network. In the embodiments described herein and in the art, the meaning of the word “packet” is to be inferred by the usage of the word.  
         [0036]     Since the subject matter of the embodiments is directed towards mobile IP telephony, the terminology of RFC 2002 (October 1996) will also be used forthwith. The protocol promulgated in this document enables a mobile wireless communication device to change the point of attachment to the Internet without having to change the IP address of the device. Namely, RFC 2002 describes a registration scheme that informs a home agent of the location of a mobile communication device so that the home agent can route data packets through foreign agents. A “home agent” is the infrastructure element that processes IP packets at the home system of the access terminal. A “foreign agent” is the infrastructure element that services the access terminal at a visited system. The access terminal is also referred to as a “Mobile Node” (MN).  
         [0037]     In reference to  FIG. 1 , the functions of a foreign agent and/or home agent can be accomplished by a PDSN  20  in a visited network or a PDSN  20  in the home network. Authentication, authorization, and accounting functions are usually performed by a server, which is referred to as an Accounting, Authorization, and Accounting (AAA) Server. The AAA server is communicatively coupled to either a PDSN and/or a BSC.  
         [0038]     In cdma2000 1xEV-DO, hereinafter referred to as EV-DO, the wireless communication system entities of  FIG. 1  are conceptually simplified to an access terminal and an access network. An access terminal (AT) is any device that allows a user to access a packet switched data network through the EV-DO wireless access network. The access network (AN) comprises any network equipment/entity that provides data connectivity between a packet switched data network and access terminals.  
         [0039]      FIG. 2  is a diagram of the data connectivity between an AT  200 , an AN  210 , an AN-AAA server  220 , and a PDSN  230 . A communication session is established between the AT  200  and the AN  210  when the AT  200  desires access to the PDSN  230 . The session is implemented according to PPP protocols and is referred to as the authentication network stream. The AN  210  communicates with the AN-AAA server  220  in order to determine whether to allow the AT  200  access to the PDSN  230 . Based upon the authentication information conveyed within the authentication network stream, the AN  210  transparently passes a service network stream between the AT  200  and the PDSN  230 . The PDSN  230  further communicates with the AN-AAA server  220  in order to determine whether to allow the AT  200  access to a packet switched data network (not shown). Based upon the authentication information conveyed within the service network stream, the PDSN  230  allows IP traffic between the packet switched data network (not shown) and the AT  200 .  
         [0040]     Hence, in an EV-DO system, an authentication procedure takes place to ensure that the AT is an authorized subscriber of the wireless network and an authentication procedure takes place to ensure that the AT is the owner of the radio session. Typically, the AT stores the authentication information and the account information required for such procedures in a secure manner. One such authentication procedure is the Challenge Handshake Authentication Protocol (CHAP). Other authentication protocols may be used without undue experimentation in the described embodiments, but for illustrative ease, CHAP will be described herein. Examples of other authentication protocols are the Mobile IP authentication protocol and the Password Authentication Protocol (PAP).  
         [0041]     In a challenge/response authentication protocol such as the ones listed above, the user is provided an unpredictable number and is challenged with the task to encrypt the unpredictable number and return a predictable result. If the user is authorized, then the user would have the correct mechanism, either in hardware or in software, to encrypt the unpredictable number in a manner that is expected by the challenger. For example, if the user is authorized, the user and the challenger would have a shared secret key that could be used to encrypt the challenge. Unauthorized users would lack the appropriate secret key to encrypt the challenge into a response that is expected by the challenger.  
         [0042]     When a device is tethered to an AT in order to use the AT as a modem to send and receive IP traffic, various complications arise regarding the authentication of the device tethered to the AT. The use of the word “tethered” herein is for describing the connectivity between a device to a wireless communication device. It is envisioned that such connectivity may be through either a physical connection, such as a cable attachments or direct contact, or a nonphysical connection, such as radio connections, optical connections, or infrared connections.  
         [0043]     For optimal performance, the tethered device would enter into PPP negotiations directly with the network. However, the tethered device may not be able to perform the authentication procedures necessary for PPP negotiations with the network because the required network security information is stored within the AT, not the tethered device. Passing the network security information from the AT to the tethered device is an option that is highly undesirable due to the potential for misuse of said security information.  
         [0044]     One solution is to perform the PPP negotiations and authentication procedures between the AT and the AN, and to subsequently perform the PPP negotiations between the AT and the tethered device without performing the authentication procedures. However, this solution is flawed in that two (2) PPP negotiations would be performed, which introduces an unacceptable time delay. Moreover, this solution is flawed in that the tethered device is not informed that authentication has occurred. It should be noted that an end-to-end PPP negotiation process requires certain procedural steps, such as in authentication, to be completed by each end before the PPP session is fully established.  
         [0045]     The embodiments that are described herein are for performing a single end-to-end PPP negotiation that enhances the security of the authentication and account information while satisfying the authentication procedures of both the tethered device and the AT.  
         [0046]     In a first embodiment, hardware within an AT is configured to perform a proxy authentication of the tethered device. Since the AT is being used as a modem for the tethered device, the terminology of the Mobile IP protocol is used in  FIG. 3 , so that the AT is referred to as a mobile node (MN).  FIG. 3  illustrates the high level procedure for the proxy authentication. At instance  300 , a tethered device and a PDSN/IWF commence a PPP session using the Link Control Protocol (LCP). LCP is used to establish, configure, maintain and terminate the PPP session. The MN acts as a transparent link between the tethered device and the PDSN/IWF. At instance  310 , the PDSN/IWF sends a CHAP challenge to the MN. At instance  320 , the MN forwards the CHAP challenge to the tethered device. At instance  330 , the MN generates a CHAP response using a password or shared key that is already stored within the MN. Note that the MN generates the CHAP response independently of the tethered device.  
         [0047]     At instance  340 , the MN receives a CHAP response from the tethered device. Upon receipt of CHAP response from the tethered device, the MN intentionally withholds transmission of the CHAP response from the tethered device to the PDSN/IWF.  
         [0048]     At instance  350 , the MN receives a CHAP success/failure indicator from the PDSN/IWF. At instance  360 , the MN forwards the CHAP success/failure indicator to the tethered device.  
         [0049]     Hence, in the manner described above, the first embodiment allows the MN to perform a proxy authentication of a tethered device using CHAP. In other aspects of the embodiment, other challenge/response authentication protocols such as PAP and Mobile IP Authentication may be used. In another embodiment, the MN may interchange the timing of instances  320  and  330 , so that the MN may generate a response to the challenge before forwarding the challenge to the tethered device.  
         [0050]     In general, the MN acts to intercept a challenge directed to the tethered device, generates an appropriate response to the challenge without waiting for input from the tethered device, forwards the challenge to the tethered device, and ignores the challenge response generated by the tethered device.  
         [0051]     If the response generated by the MN is lost, which may occur due to the error-prone nature of the wireless environment, then subsequent challenges retransmitted from the network will ensure that the authentication procedure is completed.  
         [0052]     In order to ensure that encrypted authentication is employed, the MN may also generate a response to the LCP Configuration-Request message (C-REQ) that precedes the PPP authentication phase without waiting for input from the tethered device. The use of encrypted authentication is preferred for wireless networks, but may not be a requirement of the terminal equipment, such as a tethered device. (Since the embodiments are equally applicable to situations where the terminal equipment is not “tethered” to the wireless modem, such as in a dual-processor device, the more general term of “terminal equipment” will be used herein.) Since in the pseudo-netmodel mode of operation the wireless modem is not the PPP endpoint, the wireless modem may not control the LCP configuration exchange. Authentication and account information may reside in the wireless modem, rather than in the terminal equipment, in order to provide enhanced network security and/or simplify the device and software architectures. However, if a non-encrypted authentication protocol (e.g., PAP) is used to establish a wireless network communication link, the authentication credentials will be transmitted over the air in clear text which makes them vulnerable to interception by eavesdropping equipment. Thus, the use of a non-encrypted authentication protocol increases the risk of network access by unauthorized users who obtain authentication credentials by using eavesdropping techniques. To reduce this risk, the MN can be configured to enforce encrypted authentication protocols by directly generating a response to an LCP configuration request message that proposes the use of authentication but not encrypted authentication.  
         [0053]     One of the configuration options defined for the PPP LCP protocol is Authentication-Protocol. Values contained within the LCP configuration request (C-REQ) message may be used to indicate the type of authentication protocol, if any, that is proposed. Thus, by comparing the value to an initialization table, a receiving processor can determine the type of authentication protocol that is being proposed.  
         [0054]     Generation of an appropriate response by the MN to a configuration request directed to the tethered device depends upon whether authentication is indicated in the LCP authentication request.  FIG. 4  illustrates a general process by which the MN can respond to LCP configuration request (C-REQ) messages depending upon the authentication protocol indicated in the value field of the LCP Authentication-Protocol (AP) option. In order to determine the appropriate response to an to LCP configuration request message  410  from an PDSN/IWF device, the MN parses the request to read the authentication protocol (AP) value, step  420 . If the AP value in the LCP configuration message is set to no authentication, step  430 , then the configuration request is passed to the terminal device, step  440 , with the MN acting as a transparent link between the tethered device and the PDSN/IWF. However, if the AP value in the LCP configuration request message indicates that authentication is proposed by the PDSN/IWF, then the MN tests whether the AP value corresponds to an acceptable authentication protocol, step  450 . If the AP value is acceptable, then the configuration request message is forwarded on to the terminal equipment, step  460 . However, if the AP value is unacceptable, then the MN generates an appropriate response to the PDSN/IWF indicating that the AP value is unacceptable, step  470 . This message may be in the form of a configuration not acceptable (C-NAK) message which specifies a value that is acceptable, step  480 . For example, the C-NAK message could specify that the AP value is unacceptable by proposing an acceptable value, such as CHAP. The process illustrated in  FIG. 4  is repeated until either an acceptable AP value is included in the configuration request message, or the number of retries (i.e., loops through the process) exceeds a preset number. The number of retries can be determined by a configurable retry counter that is initialized with the number of C-NAK messages that may be sent before the MN should give up authentication protocol negotiations.  
         [0055]     For example, if the LCP configuration request message (C-REQ)  410  includes an AP value indicating that PAP is proposed (i.e., AP=PAP), the MN determines that authentication is requested (step  430 ) and that the requested type of authentication is unacceptable (step  450 ). In response, the MN would send a C-NAK message  480  to the PDSN/IWF indicating that PAP (i.e., AP=PAP) is unacceptable and that CHAP (i.e., AP=CHAP) is acceptable (step  470 ). As another example, if the LCP C-REQ message  410  includes an AP value proposing that no authentication be employed (e.g., AP=0), the MN directly forwards the LCP C-REQ message  440  to the terminal equipment because communicating without authentication does not expose authentication credentials to eavesdropping. Similarly, if the LCP C-REQ message proposes CHAP (i.e., AP=CHAP), which does not transmit authentication credentials in the clear, the MN directly forwards the LCP C-REQ message  440  to the terminal equipment because this authentication protocol also does not expose authentication credentials to eavesdropping.  
         [0056]     In testing the AP value, the wireless modem can compare the value to a prioritized list of acceptable, desirable and/or unacceptable authentication protocols. The example embodiments described herein cite CHAP as an acceptable authentication protocol value and PAP as an unacceptable authentication protocol value. This is because PAP is non-encrypted, which raises the risk of authentication credentials being obtained by unauthorized parties. In contrast, CHAP is an encrypted authentication protocol presently secure from eavesdropping. The security of encrypted authentication protocols like CHAP depends in part upon the commercial unavailability of the computing power sufficient to determine the encryption key and algorithm used to generate the challenge response hash. However, it is expected that in the future commercially-available computing power will increase such that present CHAP hash algorithms may become vulnerable. For this reason, it is expected that additional encrypted authentication protocols will be developed over time to increase security (e.g., by increasing the size of keys and complexity of hashing algorithms). It is also expected that some current encrypted authentication protocols may become increasingly vulnerable to interception and compromise. Thus, it is anticipated that encrypted authentication protocols will be developed with varying degrees of vulnerability, and therefore varying levels of desirability. To accommodate this, the MN may compare the AP value in the configuration request to a prioritized list of authentication protocols, and generate an appropriate response based on the prioritized list. For example, the MN may send a C-NAK response that counter proposes the highest priority protocol in a prioritize list of protocols known or accessible to the MN. If a prioritized list of protocols is employed, the process of the MN responding directly to the PDSN/IWF will continue until the proposed authentication value received from the PDSN/IWF is acceptable to the MN. Therefore, the use of CHAP and PAP in the illustrative embodiments should not be construed as limiting the potential responses of the MN to a configuration request specifying authentication.  
         [0057]     Previously known operations of the MN during the LCP configuration exchange are described in U.S. Pat. No. 6,370,118, which is assigned to the assignee of the present invention and incorporated by reference herein. As part of the LCP process, the MN parses the configuration request to obtain the configuration options. As illustrated in  FIG. 5 , when the MN receives a LCP C-REQ message  500 , it saves the proposed configuration options if they are acceptable to the MN (i.e., the proposed configuration is supported by the wireless modem), step  5   10 . Additionally, the MN determines if the devise phase is active, step  520 , setting the device phase to ESTABLISH if not, step  530 , and determines if the bridge device phase is active, step  540 , setting the bridge device phase to ESTABLISH if not, step  550 . This enables communication with the terminal equipment, after which the configuration request message is forwarded to the terminal equipment, step  560 . This process passes the configuration request message through to the terminal equipment which generates the appropriate response.  
         [0058]      FIG. 6  illustrates an embodiment which modifies the operation of the MN during the LCP process to implement the general method illustrated  FIG. 4 . In this embodiment, the incoming configuration request message,  500 , is parsed by the MN to obtain the proposed configuration options, including the AP value, step  600 . If the AP value indicates that an acceptable authentication protocol is proposed (e.g., AP≠PAP), step  610 , then the MN process described above with reference to  FIG. 5  is implemented. However, if the AP value indicates that an unacceptable authentication protocol is proposed (e.g., AP=PAP), step  610 , then the MN queries a counter to determine if a predetermined number of retries has been exceeded, step  620 . If the number of retries has not been exceeded, the MN creates a C-NAK response message that indicates an AP value acceptable to the MN (e.g., AP=CHAP), step  630 , which is sent to the PDSN/IWF over the Um link, step  650 , and decrements the retry counter. If the number of retries has been exceeded, this indicates that the PDSN/IWF is unable to propose an acceptable authentication protocol. In this case, the MN creates a configuration rejection (C-REJ) response message indicating that authentication is an unacceptable configuration parameter, step  640 , which is sent to the PDSN/IWF over the a wireless link, step  650 . (In common parlance, the data link between the wireless modem and terminal equipment is referred to as the Rm link or Rm side, while the wireless link between the wireless modem and the PDSN/IWF is referred to as the Um link or the Um side.) In each case where the proposed configuration was unacceptable to the MN, there is no need for the MN to forward the configuration request message to the terminal equipment.  
         [0059]      FIG. 7  illustrates an exchange of messages in an example LCP configuration exchange leading to agreement on an acceptable authentication protocol. Initiation of the LCP process may begin with an LCP configuration request message (C-REQ)  700  sent by the terminal equipment proposing configurations acceptable to the terminal equipment, which is passed through the MN to the PDSN/IWF without modification. In response, the PDSN/IWF will send an acknowledgement message  710 , if the proposed configurations are acceptable. The PDSN/IWF then sends a configuration request message (C-REQ)  720  proposing an authentication protocol and other configuration option values. If the proposed application protocol is unacceptable, such as AP=PAP, the mobile node directly responds to the PDSN/IWF with a C-NAK message  730  counter-proposing an acceptable authentication protocol, such as AP=CHAP. In the event that the authentication protocol proposed by the MN in the C-NAK message  730  is acceptable to the PDSN/IWF, the PDSN/IWF sends a new configuration request message (C-REQ)  740  proposing an authentication protocol equal to the acceptable value (e.g., CHAP) along with the other configuration option values. Since the proposed authentication protocol is acceptable to the MN, the configuration request message is passed through to the terminal equipment which responds with an acknowledgement C-Ack message  750  indicating that the configuration has been accepted, thereby completing negotiations of the configuration. The PPP negotiations between the terminal equipment the PDSN/IWF may continue for a while until both sides agree on a negotiated configuration. Once the configuration has been successfully negotiated, the authentication challenge process described above with reference to  FIG. 3  proceeds.  
         [0060]      FIG. 8  illustrates an exchange of messages in an example LCP configuration exchange leading to a communication configuration in which no authentication protocol is employed. In this example, the messages described above with reference to  FIG. 7  are exchanged until the preset number of retries has been exhausted (i.e., no C-NAK retries remain, step  620  in  FIG. 6 ). When the next configuration request (C-REQ) message  810  is received from the PDSN/IWF proposing an unacceptable authentication protocol, the MN responds directly to the PDSN/IWF by sending a configuration reject (C-REJ) message  820  indicating that authentication protocol is rejected as a configuration option. In this example, the PDSN/IWF can accept a configuration in which there is no authentication, and accordingly, sends a configuration request message  830  which does not propose authentication and proposes the other configuration option values. Since there is no unacceptable authentication protocol proposed in the configuration request, the MN and passes the configuration request message on to the terminal equipment. If the terminal equipment accepts all of the other configuration values, it responds with a configuration acknowledgement (C-ACK) message  840 . Thereafter the LCP process proceeds without the authentication challenge process illustrated in  FIG. 3 .  
         [0061]      FIG. 9  illustrates the exchange of messages in an example LCP configuration exchange which concludes in termination of the communication attempt because no acceptable configuration could be negotiated. In this example, the messages described above with reference to  FIG. 7  are exchanged until the preset number of retries has been exhausted (i.e., no C-NAK retries remain, step  620 ). When the next configuration request message  910  is received from the PDSN/IWF proposing an unacceptable authentication protocol, the MN responds directly to the PDSN/IWF by sending a configuration reject (C-REJ) message  920  indicating that authentication protocol is rejected. In this example, the PDSN/IWF cannot accept a configuration in which there is no authentication, and accordingly, sends a communication termination request (TERM-REQ) message  930 . Since no authentication protocol is proposed in this message, the MN passes the message through to the terminal equipment which responds with a termination acknowledgment (TERM-ACK) message  940 , after which the communication link will be discontinued.  
         [0062]      FIG. 10  illustrates an embodiment which promptly terminates the communication link in the event that an acceptable authentication protocol cannot be negotiated. This embodiment may be implemented where it is known that the authenticator requires authentication, in which case sending a configuration rejection message rejecting authentication protocol will be a waste of time and communication bandwidth. In this embodiment, the incoming configuration request (C-REQ) message,  500 , is parsed in the MN to obtain the configuration options, including the AP value, step  600 . If the AP value indicates that an acceptable authentication protocol is proposed (e.g., AP≠PAP), step  610 , then the MN process described above with reference to  FIG. 5  is implemented. However, if the AP value indicates that an unacceptable authentication protocol is proposed (e.g., AP=PAP), step  610 , then the MN tests a counter to determine if a predetermined number of retries has been exceeded, step  620 . If the number of retries has not been exceeded, the MN creates a C-NAK response message indicating that an AP value equal to CHAP is acceptable which is sent to the PDSN/IWF over the Um link, step  1010 . If the number of retries has been exceeded, which indicates that the PDSN/IWF is unable to propose an acceptable authentication protocol, the MN takes a preemptive action to terminate the communication link. Specifically, the MN sends a termination request (TERM-REQ) message to the PDSN/IWF which stops the PPP connection with the network,  1020 . Similarly, the MN sends a termination request (TERM-REQ) message to the terminal equipment which stops the PPP connection with the terminal equipment,  1030 .  
         [0063]     The message exchanges of the embodiment illustrated in  FIG. 10  are illustrated in  FIG. 11  for the case where an acceptable authentication protocol cannot be negotiated. In this example, the messages described above with reference to  FIG. 7  are exchanged until the preset number of retries has been exhausted (i.e., no C-NAK retries remain, step  620 ). When the next configuration request (C-REQ) message  1100  is received from the PDSN/IWF proposing an unacceptable authentication protocol, the MN responds directly to the PDSN/IWF by sending a termination request (TERM-REQ) message  1110 , which the PDSN/IWF responds to by sending a termination acknowledgement (TERM-ACK) message  1140 . Without waiting for an acknowledgement, the MN may also send a termination request (TERM-REQ) message  1120  to the terminal equipment, which will respond with a termination acknowledgement (TERM-ACK) message  1130 .  
         [0064]     While the foregoing embodiments have been described in the context of a terminal device coupled to a wireless modem connecting via a wireless data link to a network, the invention has broader applicability. For example,  FIG. 12  illustrates a protocol stack of a dual mode processor configuration which can employ the foregoing embodiments. In this example, the terminal processor  1210  is coupled to a mobile processor  1220  which is configured to control communications with a PDSN/IWF via a wireless communication link. The terminal processor  1210  and mobile processor  1220  communicate by any of a number of potential electrical connection configurations and protocols, such as appropriate between two processors within a dual processor architecture. As illustrated in  FIG. 12 , the two processors  1210 ,  1220  communicate by a processor-to-processor relay layer  1212 ,  1222  which may be firmware (i.e., circuit connections) or a combination of firmware and software. Above this level may be the point-to-point protocol PPP layer  1214 , various network layer protocols  1216 , and upper layer protocols  1218  as well as application software. Within the mobile processor  1220 , various communication protocols necessary to support wireless messaging Internet communication may be provided, including, for example, a mobile IP layer  1229 , a user datagram protocol (UDP) layer  1228 , an Internet protocol layer  1227  and a point-to-point protocol PPP layer  1226 . Communication with an external wireless node  1230  can be provided through a radio link protocol (RLP) layer  1225  communicating with a IS-95 protocol layer  1224 , which correspond with similar layers  1232 ,  1234  in the external wireless node  1230 . The radio link protocol (RLP)  1225 ,  1234  (which is defined in IS-707.2) and IS-95 protocol  1224 ,  1232  are both well known in the art for use in transmitting data packets which can be encapsulated in PPP frames.  
         [0065]     As can be seen from  FIG. 12 , the present invention may be applicable to any situation in which a terminal processor is coupled to modem processor which serves as an intermediary communication node and a link to another processor or network. For example, the terminal processor could be a second processor within a mobile handset (e.g., a cellular telephone) in which a first processor controls the wireless modem and passes communications to the second processor which may be dedicated to running mobile applications. In such a device, authentication credentials may be stored in the first processor, so that processor should be configured according to the present invention to ensure that no unencrypted authentication protocol is employed in wireless communications between the second processor and an external computer or network. Similarly, the methods of the present invention may be employed in a dual processor computer architecture, where one processor functions as the terminal equipment while another processor holds the authentication credentials and performs modem type functions in a pseudo-netmodel operation, thus presenting itself as a mobile node to a network. Consequently, the uses of terms such as terminal device, terminal equipment, mobile node and wireless modem to describe the various embodiments are not intended and should not be construed to limit the scope of the invention to a device tethered to a wireless modem.  
         [0066]     The hardware used to implement the events of forgoing embodiments may be processing elements and memory elements configured to execute a set of instructions, wherein the set of instructions are for performing method steps corresponding to the above events. Alternatively, some events may be performed by circuitry that is specific to a given function. For example, the generation of a challenge response may be performed by linear feedback shift registers and adders configured to implement hashing functions or other encryption algorithms.  
         [0067]     Those of skill in the art would 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.  
         [0068]     The 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.  
         [0069]     The 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 that 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.  
         [0070]     The 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 spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.