Patent Publication Number: US-7224678-B2

Title: Wireless local or metropolitan area network with intrusion detection features and related methods

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of wireless networks, and, more particularly, to wireless local and metropolitan area networks and related methods. 
   BACKGROUND OF THE INVENTION 
   Wireless networks have experienced increasing development over the past several years. Two particular examples are the wireless local area network (LAN), and the wireless metropolitan area network (MAN). In a basic service set (BSS), such networks include one or more wireless stations (e.g., a laptop with a wireless network interface card (NIC)) that communicate with an access point or base station (e.g., a server) via radio frequency signals, for example. The base station performs numerous functions, such as synchronization and coordination, forwarding of broadcast packets, and providing a bridge between the wireless LAN/MAN and a wired network, such as telephone network, for example. 
   In an extended service set (ESS), multiple base stations are included in the network. On the other hand, in some wireless LANs/MANs there may be no base stations at all, only wireless stations engaging in peer-to-peer communications with one another. This topology is called an independent basic service set (IBSS), and in an IBSS one of the wireless stations is typically elected to act as a proxy for the missing base station. 
   Perhaps the most significant reason for the popularity of wireless LANs/MANs is that such networks are relatively inexpensive and easy to deploy in that a wired infrastructure is not required. Yet, wireless LANs/MANs also have several significant drawbacks not found in wired networks. For example, because wireless LAN/MAN devices are so prevalent, such devices are readily available to would-be hackers who may attempt to intrude upon the network and compromise network security using an unauthorized wireless station (i.e., a rogue station). Also, if wireless LANs/MANs are operated too closely to one another the networks may intrude upon one another and cause network disruption, particularly if they share common channels. 
   One of the more prominent standards which has been developed for regulating communications within wireless LANs/MANs is that of the Institute of Electrical and Electronic Engineers&#39; 802 LAN/MAN Standards Committee, entitled “IEEE Standards for Information Technology—Telecommunications and Information Systems—Local and Metropolitan Area Network—Specific Requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications,” 1999, which is hereby incorporated herein in its entirety by reference. In addition to providing wireless communications protocols, the 802.11 standard also defines a wired equivalent privacy (WEP) algorithm which is used to protect wireless signals from eavesdropping. More particularly, WEP provides for the encryption of messages to be sent between stations as well as an integrity check to ensure that the integrity of the originally transmitted messages has not been compromised. 
   While the WEP algorithm does provide some measure of network security, it does not detect or report potential intrusions into the network. Only recently have such intrusion detection systems been made available. These systems typically include security monitoring software to be installed on stations where intrusion detection is desired. Such software may attempt to detect intruders by monitoring and recording media access control (MAC) addresses or Internet protocol (IP) addresses and comparing them to known addresses of authorized network stations. Furthermore, such systems may observe when WEP is not enabled. 
   One particular example of an intrusion detection system from WildPackets, Inc. is called AiroPeek. AiroPeek searches for unauthorized rogue stations based upon ESS and BSS identifications (ESSIDs, BSSIDs) in use in the network. That is, a list of all authorized BSSIDs and ESSIDs in use in the network is created. A filter is then used to exclude all unauthorized stations. This filter is created by capturing normal network traffic and determining the data offset in an 802.11 frame corresponding to the ESSID or BSSID. AiroPeek also includes an alarm that is triggered on the basis of frame count. That is, if the frame count exceeds zero, the alarm is triggered (i.e., if any frames are detected from a rogue station, then the alarm is triggered). Further, AiroPeek can provide notification of an alarm via email or by using a modem to dial out of the system (e.g., to a pager). 
   Despite the advancements made by the above systems, some intrusions into a wireless LAN/MAN may still go undetected by such systems. That is, if a rogue station has obtained access to an authorized address and/or ID, for example, the above approaches may not detect the intrusion of the rogue station into the network. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing background, it is therefore an object of the present invention to provide a wireless LAN/MAN with intrusion detection features and related methods. 
   This and other objects, features, and advantages in accordance with the present invention are provided by a wireless local or metropolitan area network which may include a plurality of stations for transmitting data therebetween using a media access (MAC) layer, where each of the stations has a respective MAC address associated therewith. The wireless network may also include a policing station for detecting intrusions into the wireless network. This may be done by monitoring transmissions among the plurality of stations to detect frame check sequence (FCS) errors from a MAC address, and generating an intrusion alert based upon detecting a number of FCS errors for the MAC address exceeding a threshold. 
   Furthermore, the policing station may detect intrusions into the wireless network by monitoring transmissions among the plurality of stations to detect failed attempts to authenticate MAC addresses, and generating an intrusion alert based upon detecting a number of failed attempts to authenticate a MAC address. More specifically, the policing station may generate an intrusion alert based upon detecting the number of failed attempts to authenticate a MAC address within a predetermined period. 
   In addition, the plurality of stations may transmit request to send (RTS) and clear to send (CTS) packets therebetween prior to transmitting data. The RTS and CTS packets typically include a network allocation vector (NAV) indicating a time duration reserved for transmitting the data. As such, the policing station may further detect intrusions into the wireless network by monitoring the RTS and CTS packets sent between the plurality of stations to detect an illegal NAV value therein and generate an intrusion alert based thereon. 
   The plurality of stations may also intermittently operate in a contention-free mode during a contention-free period (CFP). Thus, the policing station may also advantageously detect intrusions into the wireless network by monitoring transmissions among the plurality of stations to detect contention-free mode operation outside of a CFP (or vice versa) and generate an intrusion alert based thereon. 
   Additionally, the wireless network may have at least one service set ID associated therewith, such as a BSSID and/or an ESSID, for example. Accordingly, the policing station may further detect intrusions into the wireless network by monitoring transmissions among the plurality of stations to detect service set IDs associated therewith. The policing station may further generate an intrusion alert based upon one of the detected service set IDs being different than the at least one service set ID of the wireless network. Also, the plurality of stations may transmit data over at least one channel, and the policing station may detect transmissions over the at least one channel not originating from one of the plurality of stations and generate an intrusion alert based thereon. 
   The policing station may advantageously transmit an intrusion alert to at least one of the plurality of stations in some embodiments. As such, the appropriate countermeasures may be taken to respond to the intrusion. Further, the policing station may include one or more base stations and/or wireless stations. 
   An intrusion detection method aspect of the invention is for a wireless local or metropolitan area network including a plurality of stations. The method may include transmitting data between the plurality of stations using a MAC layer, where each of the stations has a respective MAC address associated therewith. Moreover, transmissions among the plurality of stations may be monitored to detect FCS errors from a MAC address, and an intrusion alert generated based upon detecting a number of FCS errors for the MAC address exceeding a threshold. 
   Additionally, the method may also include monitoring transmissions among the plurality of stations to detect failed attempts to authenticate MAC addresses, and generating an intrusion alert based upon detecting a number of failed attempts to authenticate a MAC address. In particular, an intrusion alert may be generated based upon detecting a number of failed attempts to authenticate a MAC address within a predetermined period. 
   Furthermore, the method may include transmitting RTS and CTS packets between the plurality of stations prior to transmitting data. As noted above, the RTS and CTS packets typically include NAV values indicating a time duration reserved for transmitting the data. Moreover, the RTS and CTS packets transmitted between the plurality of stations may be monitored to detect an illegal NAV value therein, and an intrusion alert generated based upon the detected illegal NAV value. 
   The plurality of stations may intermittently operate in a contention-free mode during a CFP. As such, the method may also include monitoring transmissions among the plurality of stations to detect contention-free mode operation outside of a CFP (or vice versa), and generating an intrusion alert based thereon. 
   In addition, the wireless network may have at least one service set ID associated therewith. Thus, the method may further include monitoring transmissions among the plurality of stations to detect service set IDs associated therewith, and generating an intrusion alert based upon one of the detected service set IDs being different than the at least one service set ID of the wireless network. Here again, the service set IDs may be ESSIDs and/or BSSIDs, for example. Also, the plurality of nodes may transmit data over at least one channel. Transmissions over the at least one channel not originating from one of the plurality of stations may therefore be detected, and an intrusion alert generated based thereon. The method may also include transmitting the intrusion alert to at least one of the plurality of stations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of a wireless LAN/MAN in accordance with the present invention for providing intrusion detection based upon frame check sequence (FCS) errors. 
       FIG. 2  is a schematic block diagram of an alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon failed authentications of media access control (MAC) addresses. 
       FIG. 3  is a schematic block diagram of another alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon illegal network allocation vectors (NAVs). 
       FIGS. 4 and 5  are schematic block diagrams of further alternate embodiments of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon contention-free mode operation outside of a contention-free period (CFP) and based upon contention mode operation during a CFP, respectively. 
       FIG. 6  is a schematic block diagram of another alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon transmissions occurring during an unauthorized period. 
       FIG. 7  is a schematic block diagram of still another alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon detecting integrity check values which do not correspond with their respective data packets. 
       FIG. 8  is a schematic block diagram of yet another alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon detecting usage of non-consecutive MAC sequence numbers by a station. 
       FIG. 9  is a schematic block diagram of another alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon detecting collisions of packets having a predetermined packet type. 
       FIG. 10  is a schematic block diagram of yet another alternate embodiment of the wireless LAN/MAN of  FIG. 1  for providing intrusion detection based upon detecting collisions of a same MAC address. 
       FIG. 11  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting FCS errors. 
       FIG. 12  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting failed authentications of MAC addresses. 
       FIG. 13  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting illegal network allocation vector (NAV) values. 
       FIGS. 14 and 15  are flow diagrams illustrating intrusion detection methods in accordance with the present invention based upon detecting contention-free mode operation outside of a CFP and detecting contention mode operation during a CFP, respectively. 
       FIG. 16  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting transmissions occurring during an unauthorized period. 
       FIG. 17  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting integrity check values which do not correspond with their respective data packets. 
       FIG. 18  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting usage of non-consecutive MAC sequence numbers by a station. 
       FIG. 19  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting collisions of packets having a predetermined packet type. 
       FIG. 20  is a flow diagram illustrating an intrusion detection method in accordance with the present invention based upon detecting collisions of a same MAC address. 
       FIG. 21  is a flow chart illustrating additional method aspects of the invention for intrusion detection. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
   For purposes of the foregoing discussion, like numbers refer to like elements throughout. Moreover, referring particularly to  FIGS. 1–10 , reference numerals differing by decades are used to indicate similar elements in alternate embodiments. For example, the wireless stations  11 ,  21 ,  31 ,  41 ,  51 ,  61 ,  71 ,  81 ,  91 , and  101  illustrated in  FIGS. 1–10  are all similar elements, and so on. As such, these elements may only be described in detail upon their first occurrence to avoid undue repetition, but later occurring elements are understood to be similar to those first described. 
   Referring now to  FIG. 1 , a wireless LAN/MAN  10  in accordance with the present invention illustratively includes a wireless station  11  and a base station (or access point)  12 . While only a single wireless station  11  and base station  12  are shown for clarity of illustration, those of skill in the art will appreciate that any number of wireless and/or base stations may be included within the wireless network  10 . 
   Before describing the wireless network  10  in further detail, a brief discussion regarding wireless LAN/MAN protocols is warranted. In particular, the foregoing discussion will assume a network implementation using the 802.11 standard for clarity of explanation. However, those of skill in the art will appreciate that numerous aspects and embodiments described herein may also be used with other suitable wireless LAN/MAN standards (e.g., Bluetooth, etc.). 
   The 802.11 standard is for use with the OSI network model for data transfer, which includes seven layers at which certain types of data are sent using various protocols. These layers include the application layer, presentation layer, session layer, transport layer, network layer, data link layer, and physical layer. The data link layer further includes media access control (MAC) and logical link control sub-layers. The wireless station  11  and base station  12  in particular use the MAC layer for transmitting data therebetween, particularly respective MAC addresses associated therewith, for example. Of course, the remaining layers of the OSI model may also be used for data transmission as well. Moreover, data is typically sent in packets, and various packets types are used for different types of message data, as will be described further below. 
   In accordance with the invention, the wireless network  10  illustratively includes a policing station  13  for detecting intrusions into the wireless network by a rogue station  14 . By way of example, the rogue station  14  may be used by a would-be hacker attempting to hack into the wireless network  10 , or it may simply be a node from a different wireless network that is operating too closely to the wireless network  10 . The policing station  13  may include one or more of a wireless station and/or a base station. In the present example, the policing station  13  monitors transmissions among the stations  11 ,  12  to detect frame check sequence (FCS) errors from a MAC address. If a number of FCS errors detected for a given MAC address exceeds a threshold, the policing station  13  generates an intrusion alert based thereon. 
   It should be noted that, as used herein, the phrase “transmissions among the stations” is intended to mean any transmission directly to or from one of the stations  11 ,  12 , as well as any transmission within an operating range of the wireless network  10 . In other words, the policing station  13  may monitor transmissions directed to or originating from the stations  11 ,  12  as well as any other transmissions it may receive whether or not they are specifically directed to or originate from a station in the network  10 . 
   In the above described embodiment (and those described below), the policing station  13  may advantageously transmit the alert to one or more of the stations  11 ,  12  in the wireless network  10 . By way of example, the policing station  13  may transmit the intrusion alert directly to the base station  12 , which may then notify all of the remaining stations in the wireless network. Alternately, the policing station  13  may broadcast the intrusion alert to all network stations. In either case, the appropriate countermeasures may then be taken to respond to the unauthorized intrusion, as will be appreciated by those skilled in the art. Such countermeasures are beyond the scope of the present invention and will therefore not be discussed herein. 
   Turning now to  FIG. 2 , a first alternate embodiment of the wireless LAN/MAN  20  is now described. In this embodiment, the policing station  23  detects intrusions into the wireless network  20  by monitoring transmissions among the stations  21 ,  22  to detect failed attempts to authenticate MAC addresses. Upon detecting a certain predetermined number of failed attempts to authenticate a particular MAC address, the policing node  23  will generate an intrusion alert. 
   Any number of failed attempts may be used as the threshold for generating the intrusion alert, but it may generally be desirable to allow a station at least one attempt to authenticate its MAC address without generating the intrusion alert. Moreover, in some embodiments the policing station  23  may advantageously only generate the intrusion alert if the detected number of failures occur within a predetermined period (e.g., an hour, day, etc.). 
   In accordance with the 802.11 standard, two stations wishing to communicate with one another within a wireless LAN/MAN typically transmit request to send (RTS) and clear to send (CTS) packets therebetween prior to transmitting data. The reason for this is to avoid collisions with other transmissions. That is, since many or all of the remaining stations in the wireless LAN/MAN may be communicating on the same channel, the stations need to ensure that they are not transmitting at the same time as this could result in interference and network disruption. Moreover, RTS and CTS packets typically include a network allocation vector (NAV) indicating a time duration reserved for transmitting the data. This information is transmitted to all other stations in the wireless LAN/WAN, which will then stop transmission during the specified period. 
   Turning now additionally to  FIG. 3 , a second alternate embodiment of the wireless LAN/MAN  30  is now described in which the policing station  33  detects intrusions into the wireless network  30  by monitoring RTS and CTS packets sent between the stations  31  and  32  to detect an illegal NAV value therein. For example, the wireless network  30  may be implemented in such a way that data transmission may not exceed a certain amount of time, which will be known to all of the authorized stations participating therein. Thus, if the policing station  33  detects a NAV value outside of the allotted amount of time, it will then generate an intrusion alert based thereon. 
   Another feature of the 802.11 standard is that stations within a wireless LAN/MAN may operate in contention or contention-free modes. That is, in a contention mode all stations are required to contend for access to the particular channel being used for each packet of data that is transmitted. During a contention-free period (CFP), medium usage is controlled by the base station, which thus eliminates the need for stations to contend for channel access. 
   In accordance with a third embodiment of the wireless LAN/MAN  40  illustrated in  FIG. 4 , the policing station  43  may advantageously detect intrusions into the wireless network  40  by monitoring transmissions among the stations  41 ,  42  to detect contention-free mode operation outside of a CFP. As such, an intrusion alert may be generated by the policing station  43  based upon such detection. In other words, detection of a station operating in contention-free mode outside of a CFP indicates that this station is not an authorized station, as all authorized wireless stations will be informed by the base station  42  when a CFP has been instituted. Of course, this would also be the case when contention mode operation is detected during a CFP, and such embodiment is illustratively shown in  FIG. 5 . It will be appreciated by those skilled in the art that either one or both of the above CFP intrusion detection approaches may be implemented in a given application. 
   Referring now to  FIG. 6 , another embodiment of wireless LAN/MAN  60  is now described. Here, the policing station  63  detects intrusions into the wireless network  60  by monitoring transmissions among the stations  61 ,  62  to detect transmissions during an unauthorized period. That is, the wireless network  60  may be implemented such that no users are allowed to access the network during specified hours (e.g., between midnight and 6:00 AM). Thus, upon detecting transmissions within this unauthorized period, the policing station  63  may advantageously generate an intrusion alert. 
   Turning now additionally to  FIG. 7 , still another embodiment of the wireless LAN/MAN  70  is now described. In this embodiment, the various stations  71 ,  72  have the above described WEP feature enabled and therefore generate and transmit integrity check values with respective data packets sent therefrom. Thus, the policing station  73  detects intrusions into the wireless network  70  by monitoring transmissions among the stations  71 ,  72  to detect integrity check values which do not correspond with their respective data packets. That is, if an incorrect key stream is used to generate the message ciphertext, or if the message has been tampered with by the rouge station  84 , the integrity check value will most likely be corrupted. As such, the policing station  73  may generate an intrusion alert when such errant integrity check values are detected, as will be appreciated by those of skill in the art. 
   Still another wireless LAN/MAN  80  in accordance with the invention is now described with reference to  FIG. 8 . Typically, when the above-noted OSI network model is used, a respective MAC sequence number is generated and sent with each data packet from the stations  81 ,  82 . That is, with each successive data packet the MAC sequence number is incremented, and thus each packet has a unique MAC sequence number associated therewith. As such, the policing station  83  may detect intrusions into the wireless network  80  by monitoring transmissions among the stations  81 ,  82  to detect usage of non-consecutive MAC sequence numbers by a station, and generate an intrusion alert based thereon. 
   Turning now additionally to  FIG. 9 , another embodiment of the wireless LAN/MAN  90  is illustrated in which the policing station  93  detects intrusions into the wireless network by monitoring transmissions among the stations  91 ,  92  to detect collisions of packets having a predetermined packet type. In particular, the predetermined packet type may include management frame packets (e.g., authentication, association, and beacon packets), control frame packets (e.g., RTS and CTS packets), and/or data frame packets. The policing station  93  may thus generate an intrusion alert based upon detecting a threshold number of collisions of the predetermined packet type. 
   As used herein, “collisions” is meant to include simultaneous transmission of packets as well as transmissions within a certain time of one another. That is, if a certain type of packet is supposed to have a time delay between transmissions, (e.g., a few seconds, etc.), if two such packet types are transmitted too close together (i.e., with less than the requisite delay time between them), this would be considered a collision. By way of example, the threshold number of collisions may be greater than about three, for example, although other thresholds may be used as well. Moreover, the threshold number may be based upon the particular packet type in question, i.e., the threshold number may be different for different packet types. 
   Additionally, the threshold number may be based upon a percentage of a total number of monitored packets having the predetermined packet type. For example, if a certain percentage (e.g., greater than about 10%) of packets transmitted during a period (e.g., one hour) are involved in collisions, then the intrusion alert may be generated. Alternatively, if a certain percentage of packets out of a total number of packets monitored (e.g., 3 out of 10) are involved in collisions, then the intrusion alert may be generated. Of course, other suitable threshold numbers and methods for establishing the same may also be used. 
   Referring now to  FIG. 10 , another embodiment of the wireless LAN/MAN  100  is described in which the policing station  103  detects intrusions into the wireless network by monitoring transmissions among the stations  101 ,  102  to detect collisions of a same MAC address. That is, if multiple terminals lay claim to the same MAC address simultaneously or relatively closely to one another, then either an error has occurred or one of the stations is a rouge station  104 . As such, the policing station  103  generates an intrusion alert based upon detecting a threshold number of such collisions, e.g., greater than about three. Here again, other threshold numbers may also be used, and the threshold number may be based upon a percentage, as previously described above. 
   An intrusion detection method aspect of the invention for the wireless network  10  will now be described with reference to  FIG. 11 . Beginning at Block  110 , the method includes transmitting data between the plurality of stations  11 ,  12  using the MAC layer, as previously noted above, at Block  111 . The transmissions among the stations  11 ,  12  are monitored to detect FCS errors from one of the MAC addresses, at Block  112 . If a number of FCS errors for the MAC address exceeds a threshold, at Block  113 , an intrusion alert is generated based thereon, at Block  114 , thus ending the method (Block  115 ). Otherwise, the transmissions will continue to be monitored, as illustratively shown. 
   In accordance with a first alternate method aspect of the invention now described with reference to  FIG. 12 , the method begins (Block  120 ) with transmitting data between the stations  21 ,  22 , at Block  121 , and monitoring transmissions to detect failed attempts to authenticate MAC addresses, at Block  122 , as previously noted above. If a number of failed attempts to authenticate a MAC address is detected, at Block  123 , then an intrusion is generated, at Block  124 , thus concluding the method (Block  125 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   A second alternate method aspect of the invention will now be described with reference to  FIG. 13 . The method begins (Block  130 ) with transmitting RTS and CTS packets between the stations  31 ,  32  and then transmitting data, at Block  131 . The RTS and CTS packets transmitted between the stations  31 ,  32  are monitored to detect an illegal NAV value therein, at Block  132 , as previously described above. If an illegal NAV value is detected, at Block  133 , an intrusion alert is generated based thereon, at Block  134 , thus concluding the method (Block  135 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   Turning now to  FIG. 14 , a third alternate method aspect of the invention is now described. The method begins (Block  140 ) with transmitting data between the stations  41 ,  42 , at Block  141 , and monitoring transmissions to detect contention-free mode operation outside of a CFP, at Block  142 , as previously described above. If such operation is detected outside a CFP, at Block  143 , an intrusion alert is generated based thereon, at Block  144 , thus concluding the method (Block  145 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. The opposite case in which transmissions are monitored for contention mode operation during CFPs is illustratively shown in  FIG. 15  at Blocks  150 – 155 . Here again, both of these methods could be used in a single embodiment, though this need not always be the case. 
   A fourth method aspect of the invention will now be described with reference to  FIG. 16 . The method begins (Block  160 ) with transmitting data between the stations  61 ,  62 , at Block  161 , and monitoring to detect transmissions during an unauthorized period, at Block  162 , as previously described above. If transmissions are detected during an unauthorized period, at Block  163 , an intrusion alert is generated based thereon, at Block  164  thus concluding the method (Block  165 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   Yet another intrusion detection method aspect of the invention will now be described with reference to  FIG. 17 . The method begins (Block  170 ) with transmitting data between the stations  71 ,  72 , at Block  171 , and monitoring transmissions  172  to detect integrity check values which do not correspond with their respective data packets, as previously described above. If this is the case, an intrusion alert is generated, at Block  173 , thus ending the method (Block  175 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   Turning now to  FIG. 18 , still another method aspect of the invention is described. The method begins (Block  180 ) with transmitting data between the stations  81 ,  82 , at Block  181 . Thus, the method may also include monitoring transmissions to detect usage of non-consecutive MAC sequence numbers by a station, at Block  182 , as previously described above. If such usage is detected, at Block  183 , an intrusion alert is generated, at Block  184 , thus ending the method (Block  185 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   Referring additionally to  FIG. 19 , another method aspect of the invention begins (Block  190 ) with transmitting data packets between the stations  91 ,  92 , at Block  201 , and monitoring transmissions to detect collisions of packets having a predetermined packet type, as noted above, at Block  192 . If a threshold number of collisions of packets having the predetermined packet type are detected, at Block  193 , then an intrusion alert is generated, at Block  194 , ending the method (Block  195 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   Another intrusion detection method aspect of the invention will now be described with respect to  FIG. 20 . The method begins (Block  200 ) with transmitting data between the stations  101 ,  102 , and monitoring transmissions to detect collisions of a same MAC address, at Block  202 , as previously described above. If a threshold number of collisions of a same MAC address are detected, at Block  203 , an intrusion alert is generated, at Block  204 , thus ending the method (Block  205 ). Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   Further intrusion detection aspects of the invention will now be described with reference to  FIG. 21 . As noted above, a wireless LAN/MAN typically has one or more service set IDs associated therewith, such as IBSSIDs, BSSIDs, and/or ESSIDs. As illustratively shown, beginning at Block  210  data transmission may be sent between the stations  11 ,  12 , at Block  211 , and transmissions among the plurality of stations may be monitored to detect service set IDs associated therewith and/or transmissions over a designated network channel not originating from an authorized station, at Block  212 . 
   As such, if a service set ID that is different from an authorized service set ID of the wireless network  10  and/or transmission from an unauthorized station on a network channel is detected, at Block  213 , an intrusion alert may be generated based thereon, at Block  214 . Moreover, the intrusion alert may advantageously be transmitted to one or more stations in the network, as previously described above, or to another source via modem, etc., at Block  215 . Otherwise, the intrusion monitoring may continue, as illustratively shown. 
   It will be understood by those skilled in the art that the above described method aspects may all be implemented in one or more of the wireless networks described above. Also, additional method aspects of the invention will be apparent to those of skill in the art based upon the above description and will therefore not be discussed further herein. 
   It will also be appreciated that the above described invention may be implemented in several ways. For example, the policing station  13  could be implemented in one or more separate, dedicated devices that are not already part of the wireless network  10 . Alternately, the invention may be implemented in software to be installed on one or more existing stations in a wireless LAN/MAN where intrusion detection is desired. 
   Further, many of the above-described aspects of the present invention may advantageously be used for detecting wireless network intrusion even when a rogue station has an authorized network or MAC ID (e.g., contention-free operation outside a CFP, transmission during an unauthorized period, etc.) Moreover, one or more of the above aspects may advantageously be used in a given application to provide a desired level of intrusion detection. A further advantage of the invention is that it may be used to supplement existing intrusion detection systems, particularly those that focus on intrusion in the upper OSI network layers. 
   Additional features of the invention may be found in the co-pending application Ser. No. 10/217,243 entitled WIRELESS LOCAL OR METROPOLITAN AREA NETWORK WITH INTRUSION DETECTION FEATURES AND RELATED METHODS, the entire disclosure of which is hereby incorporated herein by reference. 
   Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.