Patent Publication Number: US-2007118748-A1

Title: Arbitrary MAC address usage in a WLAN system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims benefit to provisional patent application Ser. No. 60/714,029, filed 2 Sep. 2005, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The present invention related to a method and apparatus for connecting an access point (AP) or other suitable network node to a station (STA) or other suitable network node in a wireless LAN network.  
      2. Description of Related Art  
       FIG. 1  shows, by way of example, typical parts of an IEEE 802.11 WLAN system, which is known in the art and provides for communications between communications equipment such as mobile and secondary devices including personal digital assistants (PDAs), laptops and printers, etc. The WLAN system may be connected to a wire LAN system that allows wireless devices to access information and files on a file server or other suitable device or connecting to the Internet. The devices can communicate directly with each other in the absence of a base station in a so-called “ad-hoc” network, or they can communicate through a base station, called an access point (AP) in IEEE 802.11 terminology, with distributed services through the AP using local distributed services (DS) or wide area extended services, as shown. In a WLAN system, end user access devices are known as stations (STAs), which are transceivers (transmitters/receivers) that convert radio signals into digital signals that can be routed to and from communications device and connect the communications equipment to access points (APs) that receive and distribute data packets to other devices and/or networks. The STAs may take various forms ranging from wireless network interface card (NIC) adapters coupled to devices to integrated radio modules that are part of the devices, as well as an external adapter (USB), a PCMCIA card or a USB Dongle (self contained), which are all known in the art.  
       FIGS. 2   a  and  2   b  show diagrams of the Universal Mobile Telecommunications System (UMTS) packet network architecture, which is also known in the art. In  FIG. 2   a , the UMTS packet network architecture includes the major architectural elements of user equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), and core network (CN). The UE is interfaced to the UTRAN over a radio (Uu) interface, while the UTRAN interfaces to the core network (CN) over a (wired) Iu interface.  FIG. 2   b  shows some further details of the architecture, particularly the UTRAN, which includes multiple Radio Network Subsystems (RNSs), each of which contains at least one Radio Network Controller (RNC). In operation, each RNC may be connected to multiple Node Bs which are the UMTS counterparts to GSM base stations. Each Node B may be in radio contact with multiple UEs via the radio interface (Uu) shown in  FIG. 2   a . A given UE may be in radio contact with multiple Node Bs even if one or more of the Node Bs are connected to different RNCs. For instance, a UE 1  in  FIG. 2   b  may be in radio contact with Node B 2  of RNS 1  and Node B 3  of RNS 2  where Node B 2  and Node B 3  are neighboring Node Bs. The RNCs of different RNSs may be connected by an Iur interface which allows mobile UEs to stay in contact with both RNCs while traversing from a cell belonging to a Node B of one RNC to a cell belonging to a Node B of another RNC. The convergence of the IEEE 802.11 WLAN system in  FIG. 1  and the (UMTS) packet network architecture in  FIGS. 2   a  and  2   b  has resulted in STAs taking the form of UEs, such as mobile phones or mobile terminals. The interworking of the WLAN (IEEE 802.11) shown in  FIG. 1  with such other technologies (e.g. 3GPP, 3GPP2 or 802.16) such as that shown in  FIGS. 2   a  and  2   b  is being defined at present in protocol specifications for 3GPP and 3GPP2. The reader is referred to WO 03/061203, entitled “Addressing in Wireless Local Area Networks”, which is hereby incorporated by reference in its entirety.  
      The present invention relates to such wireless LAN networks especially those according to the IEEE 802.11 standards described above. In such networks, a master slave relationship typically exists between a group of devices (usually mobile devices) called the STAs and a single coordinating device (usually fixed devices) called the AP. Messages are exchanged between each STA and the AP using a shared wireless medium. In order to ensure delivery to the correct device, each message is prefixed with address fields to identify the sender and receiver of each message. In IEEE 802.11, these are called MAC addresses. Each device is assigned globally unique MAC address during manufacture which remains with the device during its lifetime and is not reused after the device is scrapped.  
      In such wireless LAN networks, the MAC address fields attached to the messages can be read by any other compatible wireless device and system users cannot easily prevent unwanted stations from discovering the address information being used in the network.  
      The use of fixed and globally assigned MAC addresses present the following problems:  
      1) Since the addresses can be read by unwanted third party STAs the identity of STAs operating in the network might be discovered by unauthorized parties. There is no solution in current IEEE 802.11 networks to address this problem.  
      2) Since the addresses are fixed, the STA is always identified by the AP using the fixed address and it is not possible for the STA to form a new connection the AP unless the old connection can be disconnected. Under some circumstances, the STA might not be able to use or disconnect an existing connection and it thus prevented from communicating. This problem does not exist in current IEEE 802.11 systems but will occur as a result of certain changes being introduced under amendment ‘r’ thereof.  
      3) The STA is unable to make more than one simultaneous connection to the AP because it has only one MAC address. The only current solution in IEEE 802.11 networks to address this problem is to use multiple network interfaces.  
      Problems of this type have been solved for devices in other wireless networks such as cellular phone systems.  
      In the aforementioned WO 03/061203, it is known that temporary MAC addresses can be generated and their validity is checked by monitoring traffic or sending challenges. The temporary MAC may include, for example, a random number generated by means of a random number generator, organization-specific unique identifiers (OSI), a network identifier such as a BSS identifier BSSID.  
     SUMMARY OF THE INVENTION  
      In its broadest sense, the present invention provides a new and unique method and apparatus for coupling an access point (AP) or other suitable network node or terminal and a station (STA) or other suitable network node or terminal in a wireless LAN network. The present invention features the AP and the STA agreeing on an arbitrary Medium Access Address (MAC) or other suitable arbitrary address, associated with a secret value, where the arbitrary MAC is for use by the STA and the AP during a connection.  
      The arbitrary MAC address, called an “Association MAC Identifier” (AMID), may be used by the STA to form the connection with the AP and in all subsequent communications for the connection. The AP uses the AMID for example to transmit data to the STA and therefore identify the STA. The STA may also discard the AMID and acquire a new one to establish a new connection at any time or may operate with multiple AMIDs at the same time. Once an AMID is assigned to a STA, the AP prevents another STA from acquiring the same AMID value until the original STA has relinquished it or its validity has expired.  
      Alternatively, a new AMID may be selected periodically to improve security. This operation for improved security may be triggered by detection of rogue WLAN devices. Detection can be done e.g. by examining the data transmissions in the network and by determining based on the traffic pattern and combination of IP and lower level addresses such as MAC addresses that there are e.g. two WLAN terminals using the same MAC address. The traffic pattern based rogue terminal detection can be based on examining what kind of management frames are sent from a certain MAC address/IP address. The WLAN terminal may also be set to a secure mode, which uses enhanced security such as the periodic renewal of the AMID.  
      The whole thrust of the present invention is to provide for MAC address generation in a mobile terminal using a “secret” value, as well as the method to disconnect the mobile terminal.  
      In addition to the MAC address generation, the present invention also includes validity checking after which the MAC address can be used. In operation, a disconnecting procedure taking place in the AP may be initiated by a message sent by the mobile terminal.  
      The apparatus may take the form of a wireless LAN network, as well as a network node or a network element such as an AP or STA having corresponding modules configured for performing the functionality described herein.  
      One advantage of the present invention is that it disables MAC tracking and rogue disconnects described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The drawing includes the following Figures, which are not necessarily drawn to scale:  
       FIG. 1  shows typical parts of an IEEE 802.11 WLAN system, which is known in the art.  
       FIGS. 2   a  and  2   b  show diagrams of the Universal Mobile Telecommunications System (UMTS) packet network architecture, which is also known in the art.  
       FIG. 3  shows an access point (AP) according to the present invention.  
       FIG. 4  shows a station (STA) according to the present invention. 
    
    
     BEST MODE OF THE INVENTION  
      The present invention provides a new and unique method and apparatus for coupling an access point (AP) or other suitable network node or terminal  10  shown in  FIG. 3  to a station (STA) or other suitable network node or terminal  20  shown in  FIG. 4  in a wireless LAN network, consistent with that shown in  FIG. 1 . In operation, the AP  10  and the STA  20  agree on an arbitrary Medium Access Address (MAC) called association MAC identifier (AMID) or other suitable arbitrary address for use by the STA  20  during a connection. As shown, the AP  10  includes an AP/STA agreed-upon address module  12  and other access point modules  14 , while the STA  20  includes a corresponding AP/STA agreed-upon address module  22  and other station modules  24 .  
     The Basic Implementation  
      The basic implementation and cooperation of the AP  10  and STA  20  according to the present invention includes the following:  
      The AP  10  maintains a list of all AMID values that are currently assigned.  
      The AP  10  also maintains a time value the “Inactivity Time” for each AMID value and if no message is received from a STA  20  using a particular AMID value within the Inactivity Time, then that AMID value becomes invalid and is discarded by the AP  10 .  
      The AP  10  inserts into the list of AMID values a new value when it is agreed between the AP  10  and a STA  20  according to the present invention.  
      The AMID value is only used on messages exchanged between the AP  10  and STAs, such as  20 . Messages forwarded by the AP  10  to other network devices shall not use the AMID values. The AP  10  shall substitute a globally valid MAC address for the AMID in such messages.  
      The procedure for selecting and agreeing an AMID value shall be as follows: 
          The STA  20  shall observe and note AMID values used by other STAs in the target network.     The STA  20  shall randomly select a new AMID value. If the selected value matches any currently in use for the network, it shall be discarded and a new random value selected.     The STA  20  shall generate a random value called a “Commit Key” and shall store this value.     The STA  20  shall compute a value called “Commit Value” by hashing together the selected AMID and Commit key using a cryptographic algorithm known publicly such as SHA-256 (Secure Hash Signature Standard (SHS) FIPS PUB 180-2.).     The STA  20  shall send a message to the AP indicating an intent to use a new AMID value and containing the Commit Value and using the AMID as its identifying MAC address (Source MAC Address).     The AP  10  shall confirm that the proposed AMID value is not currently in use. If it is in use, the AP  10  may indicate this to the STA  20  and take no further action. If it is not in use, the AP  10  shall store the new AMID in the table and reply to the STA  20  indicating the value of Inactivity Time for the AMID.     Upon receiving the reply, the STA  20  may proceed to establish a connection to the AP  10  using the AMID as its MAC identifier. When a suitable confidentiality protocol has been established, the STA  20  may send a global MAC address to the AP  10  for use in other networks.     When the STA  20  no longer wishes to use the AMID value, it shall send a message to inform the AP  10  and shall include in the message the value of “Commit key”. The AP  10  shall compute the hash value of Commit key and AMID and confirm a match with the previously stored Commit value and, if matching, shall remove the AMID from its AMID table. Note: the use of the Commit value prevents another STA from “stealing” the AMID by forging a disconnect message.     If the STA  20  does not send any messages using the AMID for the Inactivity Time, then it shall discard the AMID and presume that its connection to the AP  10  is lost.        

      Prior to making a connection to a new AP, the STA  20  may communicate with the new AP via some other network. For example it may communicate via another AP and send messages via some backbone network connecting APs. Since the AMID may not be used in other networks, the STA  20  must use its globally assigned MAC Address to identify itself in such cases. However, the STA  20  may acquire an AMID from the target AP and then communicate the value of the AMID to the new AP via the alternative network path by including the AMID value within the body of messages. This will allow the new AP to identify the STA  20  using it AMID value when it makes a wireless connection.  
     Implementation of the Functionality of the Modules  
      The functionality of the AP  10  and STA  20  described above may be implemented in the corresponding AP/STA agreed-upon address modules  12  and  22  shown in  FIGS. 3 and 4 . By way of example, and consistent with that described herein, the functionality of the AP/STA agreed-upon address modules  12  and  22  may be implemented using hardware, software, firmware, or a combination thereof, although the scope of the invention is not intended to be limited to any particular embodiment thereof. In a typical software implementation, the module  12  and  22  would be one or more microprocessor-based architectures having a microprocessor, a random access memory (RAM), a read only memory (ROM), input/output devices and control, data and address buses connecting the same. A person skilled in the art would be able to program such a microprocessor-based implementation to perform the functionality described herein without undue experimentation. The scope of the invention is not intended to be limited to any particular implementation using technology now known or later developed in the future. Moreover, the scope of the invention is intended to include the modules  12  and  22  being a stand alone modules, as shown, or in the combination with other circuitry for implementing another module.  
      The other modules  14  and  24  and the functionality thereof are known in the art, do not form part of the underlying invention per se, and are not described in detail herein. For example, the other modules  24  may include other modules that formal part of a typical mobile telephone or terminal, such as a UMTS subscriber identity module (USIM) and mobile equipment (ME) module, which are known in the art and not described herein.  
     Advantages/Disadvantages  
      The present invention has the following advantages:  
      1) The AMID value may be assigned for a limited time and does not have an externally known algorithmic or visible connection to the STA or its MAC address.  
      2) The AMID value may be assigned to a given STA and only the “owning” STA can instruct the AP to discard the value. Therefore, other STAs cannot steal the value while it is in use.  
      3) The AMID value is discarded automatically if it is not used. Therefore, if an “owning” STA is unable to inform the AP that it does not want the value the system is self healing.  
      4) Because the system is self healing the STA can at any time select and use a new AMID if it forgets the old value or loses the Commit Key value. This avoids the current problem whereby STAs become unable to connect.  
      5) The value of the AMID chosen is not disclosed until the first message where it is also committed. This prevents and attacker from implementing a pre-emptive denial of service attack by reserving a legitimate station&#39;s MAC address for itself.  
     Motivation  
      Some motivation for the aforementioned solution is as follows:  
      The IEEE 802.11 standard has been used in a wide range of mainstream business and personal applications. The success of products has resulted in an increased dependency on IEEE 802.11 as a primary method for the interconnection of networking equipment. This increased dependence has resulted in a need for assurance that the system will not be disrupted by the actions of unauthorized equipment. Such disruption can be caused by malicious systems generating false information and impersonating valid equipment.  
      The current IEEE 802.11 standard including amendment ‘i’ (security) addresses security of data frames but systems are still vulnerable to malicious attack because management frames are unprotected. At the same time, there is an increased dependence on management frames as a result of IEEE 802.11 amendments such as IEEE 802.11h. Based on the examples of amendments ‘e’ and ‘k’, this trend is likely to continue.  
      Therefore, by reducing the susceptibility of systems to such attack, the result of the work envisioned in the present invention will be applicable and of importance to all the current applications of IEEE 802.11 and both existing and anticipated amendments.  
     Scope of the Invention  
      Accordingly, the invention comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth.  
      It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.