Abstract:
A Radio Frequency based security system for providing security for wireless Local Area Networks (WLAN) that allows the creation and maintenance of arbitrarily shaped secure wireless access areas with boundaries around said wireless Local Area Network and prevents access to the said wireless LAN from outside the perimeter of the secure area. The system includes a plurality of perimeter Radio Frequency Sentry Devices (RFSDs) that are employed to establish the boundaries of said secure area around said wireless LAN. The wireless LAN being secured may be an industry standard IEEE 802.11a, 801.11b or 802.11g based wireless LAN or any other wireless LAN that uses packet based communication protocols. The said RFSDs may be stand-alone devices or they may be connected to a wired or wireless Local Area Network.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Under 35 USC §120, this application is a divisional application and claims the benefit of priority to U.S. patent application Ser. No. 10/946,851, filed Sep. 21, 2004, entitled “Wireless Perimeter Security Device and Network Using Same”, U.S. Provisional Application No. 60/504,615, filed Sep. 22, 2003 and U.S. Provisional Application No. 60/531,972, filed Dec. 24, 2003, all of which is incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     The present invention relates generally to network security systems and more particularly to wireless local area networking systems. 
     BACKGROUND OF THE INVENTION 
     Modem communication and networking solutions are increasingly adopting radio as a communications medium. Industry standards such as the IEEE 802.11/g wireless LAN protocols, the ease of deployment, and the demand for mobile access to data and applications have fueled an explosion in the number of wireless Local Area Networks in use both in commercial as well home environments. 
     An IEEE 802.11a/b/g based wireless LAN may be constructed as shown in  FIG. 1 , with at least one radio transmitter/receiver hub called an Access Point (AP)  101 - 102  and one or more wireless devices  103 - 104 , that use these APs  101  and  102  to communicate with each other as shown by radio links  105 , or to access a network resource. The APs may be connected to a wired LAN and thus can connect a wireless device  103 - 104  to a plurality of network resources. It is relatively inexpensive to set up such a wireless LAN, which makes this a popular method for providing network access. It is estimated that there are over 500 million wireless LAN devices in use worldwide today. 
     However, the use of radio frequency as the medium brings with it a unique set of security related issues. Wireless LANs are inherently different in risk compared to a wired LAN. While in a wired LAN the layers  1  and  2  of the network typically are protected by CATS cables in a secured building, in WLANs these layers are exposed because they are implemented using radio waves and therefore cannot be contained by a physical structure such as a building. Unlike wired networks, communication in Wireless LANs is not confined to a physical link such as a CATS cable; rather, it is broadcast through the air in multiple directions simultaneously and is therefore visible, and may be intercepted and deciphered. Essentially anyone with an available radio can eavesdrop and interject traffic into a wireless networks communication stream. This use of a non-physical communication link, i.e. radio waves, makes Wireless LANs more vulnerable to security threats than wired networks which use a cable such as a CATS cable to propagate data. 
       FIG. 1  illustrates a typical enterprise Wireless LAN. In IEEE 802.11a/b/g based WLANs, wireless devices are permitted to seek out and try to connect with other wireless devices in their vicinity as shown in Wireless LAN area  106  and to form ad-hoc networks. This uncontrolled association further increases the threat to an enterprise Wireless LAN. For example, an authorized user on the corporate network can innocently connect to a neighbor&#39;s network or be maliciously lured to connect to an undesirable or unauthorized wireless device outside of the company premises and thereby compromise the entire corporate network. For reasons such as these, mechanisms to secure Wireless LANs have become an area of great interest and a huge business opportunity. 
     Two key factors have driven the development of WLAN Security solutions and to a great degree existing industry standards: 
     1. “Wired network security mindset,” which believes/operates on the assumption that once the access to a network is controlled, the network is safe. If data is encrypted for an added measure, then the result is foolproof security. 
     2. Failure of solutions developed with this mindset has made vendors more determined to make it succeed—by developing stronger access controls, stronger encryption, and dynamic keys. 
     The result is a myriad of expensive proprietary solutions that do not address the fundamental risks of using the radio frequency (RF) medium, and which, therefore, do not decrease the threats. Most of these passive solutions are cumbersome to deploy, because they do not take advantage of existing wired network infrastructure and they are economically prohibitive to maintain. 
     PRIOR ART 
     Most existing attempts to provide security for industry standard IEEE 802.11a/b/g Wireless LANs may be categorized as follows: 
     1. WEP based security solutions. This is the most basic form of security that is provided in a wireless LAN where a fixed secret code or key known only to authorized users of the WLAN is used to restrict access to only those wireless devices that have the correct secret code or key available to them. This scheme is based on an RC4 encryption algorithm, has been compromised and is no longer considered to be a viable security solution. 
     2. WPA/802.1x based security solutions. This scheme was invented to overcome the shortcomings of WEP. This scheme involves dynamic keys and the authentication of the key each time a wireless device attempts to connect to the network. This scheme has also been compromised. There are several issues with Key management and weakness in the cryptography scheme. It has been shown that it is possible to decipher the secret key and gain unauthorized access to the wireless LAN. It is widely accepted that this method does not provide adequate security for a wireless LAN. 
     3. Virtual Private Networks (VPNs). This mechanism was adopted from the wired LAN side. Security is provided by creating virtual connections between wireless devices and their destination by virtue of encrypting the data transfer between them that is not decipherable by an unauthorized entity. This scheme works well in the wired LAN domain because the data is transmitted over a physical link such as a CATS cable. Unless someone can tap into that CATS cable, they cannot view the encrypted data stream. However, in the case of a wireless LAN, the data stream may be intercepted by a radio eavesdropper and potentially decoded. More importantly, it would be possible for a hostile entity to merely establish an ad-hoc connection with the authorized wireless device at one end of the virtual path and camouflage itself as if it were the authorized device itself. This is referred to as spoofing. It has been demonstrated that this type of security breach is possible. 
     4. Intrusion Detection Systems. These solutions rely on their ability to detect any radio frequency activity outside a known perimeter. As such, they are rendered ineffective by hostile entities that eavesdrop using a passive or listen-only mode and thus do not generate any radio frequency activity. It is widely accepted that this solution does not provide adequate security for wireless LANs. 
     5. Perimeter Control systems. These solutions depend on their ability to differentiate between authorized and unauthorized sources of radio transmission by measuring the relative signal strength of the radio frequency carrier signal. However, naturally occurring phenomenon such as multi-path signals may easily cause Use alarms or camouflage unauthorized sources. In addition, passive eavesdropping is not detected by this solution. It is widely accepted that this solution is not ideal for providing a secure wireless LAN. 
     Thus the inability of any of these above approaches to restrict access to the radio waves carrying the Wireless LAN traffic renders them vulnerable to sophisticated radio frequency eavesdroppers and hence cannot be deemed secure. Accordingly, what is needed is a system and method to overcome these problems. The present invention addresses such a need. 
     BRIEF SUMMARY OF THE INVENTION 
     A wireless network comprising: at least one wireless device that transmits radio traffic; and at least one radio frequency security device (RFSD) for altering the radio traffic based upon a defined perimeter of the network. 
     The present invention is directed to a system and method that effectively eliminates the stated vulnerabilities of the uncontrolled radio frequency medium and unauthorized association of wireless devices in a wireless LAN by creating a secure area that physically isolates the Wireless LAN and its associated network traffic. 
     The present invention eliminates data sniffing or interception of radio waves and ensures that authorized wireless devices connect only within such secured zone. The present invention thus provides a unique and comprehensive security solution for wireless LANs. It should be clear that the present invention maybe used by itself or in conjunction with any of the said existing solutions to provide security for a wireless LAN. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a typical Enterprise Wireless LAN. 
         FIG. 2  shows a typical Enterprise Wireless LAN with external parasitic devices causing security hazard due to RF signal leakage. 
         FIG. 3  shows an Enterprise Wireless LAN with Radio Frequency security devices deployed creating a secure Wireless LAN area and denying access to external parasitic devices. 
         FIG. 4  illustrates a first example of multipath issues. 
         FIG. 5  illustrates a second example of multipath issues. 
         FIG. 6  shows examples of indoor radio frequency multi-path travel. 
         FIG. 7  shows three possible configurations of an installation on a single 100′×100′ building. 
         FIG. 8  is a block diagram of the RFSD for a single channel 802.11 type protocol set. 
         FIG. 9   a  illustrates active packet cloaking, with channel content and utilization outside the wall without RFSD installed. 
         FIG. 9   b  illustrates active packet cloaking, with channel content and utilization outside the wall with RFSD installed. 
         FIG. 10  is a flowchart for the active packet cloaking technique employed in the radio frequency security device (RFSD) for one channel of Wireless LAN. 
         FIG. 11  is an example of the RFSD to create RF sanitized environments (dagger). 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to network security systems and more particularly to wireless local area networking systems. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments and the general principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein. 
     The present invention provides for a system and method that allows for the “cloaking”, i.e., rendering of radio packets invisible, of wireless or radio wave traffic from devices within a defined space, using devices called Radio Frequency Security Devices (RFSDs) that define the perimeter of that secure space. This is shown in  FIG. 7 , which depicts a plurality of deployment choices of the present invention. The system includes one or more RFSDs  701  and an associated Central Commander unit  705  connected to each other over either a wireless (WLAN) or wired network (LAN)  715 . 
       FIG. 2  shows a typical wireless LAN (WLAN) deployed in a building. The components of this WLAN are one or more Access Points (APs)  201 - 202  and a plurality of wireless access devices  203 - 204 . The devices are connected to the APs  201 - 202  and to each other via radio connections  205 . The Access Points (AP)  201 - 202  are usually connected to a wired LAN backbone.  FIG. 2  also shows the excursion of WLAN radio traffic  207  outside the desired perimeter, i.e., the confines of the building. This enables parasitic external wireless devices  209 ,  210  and  211  to receive, decipher and interfere with the authorized and legitimate members of the WLAN. 
     The vulnerable WLAN shown in  FIG. 2  may be secured at the radio wave level by using the present invention as shown in  FIG. 3 . The secure WLAN in  FIG. 3  includes the WLAN shown in  FIG. 2  and includes AP  301 - 302 ; multiple wireless access devices  303 - 304  combined with plurality of instances of the Radio Frequency Security Devices (RFSDs)  312  placed on the perimeter of the building or secure WLAN area  307 . As shown in  FIG. 3 , there is no excursion of WLAN radio traffic beyond the perimeter  307  defined by placement of multiple instances of the RFSD  312 . This prevention of radio traffic excursion outside the desired secure perimeter prevents un-authorized or hostile wireless devices  309 ,  310  and  311  from receiving or interfering with the WLAN radio traffic from within the secure area  307 . 
     The RFSD is shown in  FIG. 8 , and includes a radio transmitter and receiver combination  803 , a micro-controller  806  and a set of antennas  801 - 802  and antenna steering units  802 , 804 . The RFSD may also include a battery unit  808 , an Ethernet controller  809  and an Infra-Red (IR) communications unit  807 . Also integrated into the RFSD is a Reverse Engineering Prevention Unit  810 , which is an electronic device that will destroy the RFSD circuitry if it is tampered with. As shown in  FIG. 3 , these RFSDs  312  create an invisible radio wall  307  around a defined space outside of which the wireless radio traffic within the said space is rendered invisible and indecipherable. In effect, radio data packets crossing the said radio frequency wall  307  are destroyed, using a technique called Active Packet Cloaking (APC), thereby rendering them invisible to unauthorized wireless devices that exist outside the secure space. The present inventive approach to “cloaking” i.e., rendering radio packets invisible, may be applied to cellular or pager networks or indoor/outdoor to wireless Local Area Networks (WLAN) and communication protocols such as IEEE 802.11 xx. Essentially this inventive approach can be applied to any packet switched digital communication. 
     Component Descriptions Antenna 
     The antennas  801  and  802  shown in  FIG. 8  used in the RFSD are directional antennas, with variable coverage pattern, and a very high front to back ratio. 
     Wireless Device 
     The wireless devices may be any known portable or transportable device as shown in  FIG. 3 , configured for wireless communications, such as a mobile telephone, personal digital assistant (PDA)  304 , pager, email devices, laptop  303 , desktop computers, printers, projectors, Access Points  301 ,  302  and  310 , repeaters, cameras or any other network-enabled device. Many of such devices may be handheld devices, but other wireless devices that are not of such a compact size could also be detected and cloaked. These mobile devices are configured to communicate with a network through a wireless interface. 
     Cloaking Description 
     Referring to  FIG. 7 , the cloaking system consists of a plurality of devices called Radio Frequency Security Devices (RFSDs)  701 , placed around a predetermined perimeter to create a secure area for a Wireless LAN of interest. The systems may be enhanced by the inclusion of at least one data processing system. The data processing system may include a user interface and includes memory to facilitate the initial setup, operation, and maintenance of the system, collectively known as the Central Commander  705 . The RFSDs may be stand-alone or may be connected to each other via a wireless or wired network  715 . The network may also include or have access to a variety of functionality and data, which may be hosted on the network or on subsystems or on systems accessible via the network, possibly via another one or more networks. 
     Defined or Secured Space Definition 
     A defined or secure space is comprised of a set of defined regions, areas or location (collectively known as “locales”). A locale may be defined as an interior or exterior space or location, or a combination thereof. For example, a conference room may be defined as a locale. Each locale is defined within the system in relationship to the digital form of the physical space (maps of the building/structure). Locales are defined with a multi-step approach, and at any time a decision may be made by the system that enough accuracy has been achieved and more steps are not required. 
     Defining the Space 
     As the first step, the placement of a plurality of RFSDs on the perimeter combined with the radiation pattern of the receiving and transmitting antennas of these RFSDs, defines accurately but in coarse-grained quality the outline of the perimeter. The second level of granularity is achieved by using the difference of signal strengths using two or more directional antennas facing in different directions. The third level of granularity is achieved by using signal-timing analysis; using Time (Difference) of Arrival (TOA or TDOA) based measurements. Locale definition should preferably be achieved without involving any RF surveys or provide training to the system, where an initial radio frequency propagation map has to be plotted and it becomes specific to an environment. 
     Time (Difference) of Arrival (TOA or TDOA) 
     Time (Difference) of Arrival (TOA or TDOA) are well-defined techniques that have been used for years for locating transmitting devices based on the fact that RF travels at a constant speed of light (an assumed constant for most practical work), so the farther the transmitter is from a receiver the longer it will take for the signal to arrive. In the preferred embodiment of the TDOA implementation in the RFSD, there are two or more receiving systems that are separated from each other by a fixed and known distance. 
     By doing a signal analysis of the two signals a very accurate determination can be made about the direction of the signal origination. The use of one or more antennas once again separated by a fixed and known distance, will give the distance of the originating signal. For example, in  FIG. 4 , the signal  412  originating from a device  406 - 407 - 408  inside the “Secured Space”  410 , will reach the four antennas  402 - 403 - 404 - 405  in the RFSD at different times and different signal strengths, depending its location. Similarly in  FIG. 5 , the signal  512  originating from a device  511 - 512 - 513  outside the “Secured Space”  510 , will reach the four antennas  402 - 403 - 404 - 405  in the RFSD at different times and with different signal strengths, depending on the location of its origin. Wireless devices  406 - 407 - 408  and  506 - 507 - 508  are shown as example locations inside and outside the “Secured Space” respectively. 
     Resolving Multi-Path Problems 
     One other major problem for location systems like the one described above results from multi-path radio waves. The problem is much more pronounced indoors, due to many more reflection surfaces present in close proximity. While there are multiple ways to combat this issue, the preferred way of doing this is achieved by doing the signal analysis in the smallest time window possible so that the multi-path does not even start taking place.  FIG. 6  depicts a few examples of how a signal from a transmitter (Tx)  601  can reach the receiver (Rx)  602 . There are an infinite number of combinations on how the signal can reach the Rx, but a few— 603 ,  604 ,  605 ,  606 ,  607 ,  608 —are shown for the purpose of this discussion. If the minimum distance between the transmitter Tx  601  and receiver Rx  602  is D meters, then the minimum time for the first signal to reach from transmitter Tx  601  to receiver Rx  602  is D/C seconds where C=speed of light in meters per sec. 
     All the other multi-path signals will reach the receiver Rx  602  after this first signal has been received. Because this system is applied to packet switched networks and not constant carriers, a very accurate determination is possible. The determination of D may be a combination of empirical and computed results. 
     Active Packet Cloaking 
     Once the secured space is defined and the RFSDs are in place along the perimeter, the RFSD is enabled to perform Active Packet Cloaking (APC). APC is the core of the “cloaking” invention. The APC system is composed of 3 major components: a receiving side, a transmitting side and control electronics. The receiving side is composed of one or more receiving systems and the transmitting side is also composed of one or more transmitting systems. The receiving and transmitting systems will typically be pointing in different directions. The two are controlled with control electronics to control when and what is to be received or transmitted. 
     Packet cloaking is achieved by identifying a packet originating from within the Secured Space and instantly transmitting an altered packet out and away from the Secured Space perimeter. The transmission is typically at the same power level as the received packet that triggered it. The net result is that a receiver outside the Secured Space cannot decipher the packets that are originating from inside the Secured Space. Any communication between devices outside the secured area will work unaffected, as only the packets originating from within the Secured Space are being altered. 
     For example—The IEEE 802.11alb/g protocols use the half duplex CSMA/CA protocol for access arbitration. CSMA/CA allows multiple people to use a single communication channel, with only one person transmitting at a time. With the present invention, i.e., the “Cloaking” system in place, the channel usage remains unaltered and identical to that prior to the introduction of said “Cloaking” system. The only difference now is that the slot being used by a transmitter inside the Secured Space now contains altered data as opposed to the original valid IEEE 802.11/g packet. 
     Shown in  FIGS. 9A and 9B  are three pairs of IEEE 802.11/g compliant wireless devices, communicating on the same channel. The authorized devices  902 - 903 - 904  are inside the “Secured Space”; the two outside devices  910 - 912  are on an independent network outside the “Secured Space” on the same channel; and the parasite device  920  is a malicious station that is listening to both inside WLAN traffic  905  and outside WLAN traffic  915 . 
       FIGS. 9   a  and  9   b  the show the wireless packet stream  950  and channel utilization for the above environment. To demonstrate the principle clearly a perfect scenario is assumed, with fixed length packets  905 - 915 , no wasted slots and no random back off interval, etc. The packet stream  950  consists of a sequence of packets from both the inside WLAN  905  and the outside WLAN  915  in a chronological order. As shown in  FIG. 9   a , with the RFSDs absent, the individual packets  905 - 915  are clearly visible in the stream  950  outside the “Cloaked Space”. 
     When the RFSD  901  is present only the packets  905  originating from within the “Cloaked Space” going past the RFSD  901  perimeter, are cloaked and effectively destroyed as shown by the packets  000  in the packet stream  950  illustrated in  FIG. 9   b , thereby creating an “invisible wall”, for the packets. The net result is that the channel utilization remains unaltered for the inside WLAN traffic  905  and the outside WLAN traffic  915 , just that the “outsiders” cannot see the “insiders” wireless traffic. The parasite wireless device  920  now can still listen to the valid communication  915  of the outside or unprotected WLAN, and none of the two outside wireless devices see/hear the inside or protected WLAN traffic  905 . Outside the secure perimeter WLAN traffic packets that originate from within the secure area appear as blank packets  000  in the packet stream  950 . 
     The inside network, however, will see the outside WLAN, but can never connect to it, as any packets coming from the inside, going outside are destroyed. In order for the inside network not to see the outside, the RFSDs may be enhanced to prevent the outside radio packets from entering the Secured Space in the similar manner. 
     Flow Chart of APC 
       FIG. 10  is a flowchart which describes the Active Packet Cloaking Technique employed in the RFSD for one channel of Wireless LAN. 
     Self-Tuning Mode 
     An RFSD gathers and maintains information about its surrounding peers and their status to maintain redundancy and allow for self-healing of the network, in case the need arises. Self-healing would be required in case one of the RFSDs malfunctions or executes at reduced power levels due to a failure or partial failure in the RFSD or the data processing system. 
     The central controller typically triggers the self-tuning mode. However, as an alternative, the RFSDs can initiate this action independently as well. The system sets itself up by having one or more RFSD transmit and the others listen, in multiple combinations, to gather sufficient data about the radio frequency environment, to create a Radio Frequency map of the area. This mode can be triggered periodically during idle time, based on a configuration or a default factory setting. Corrective actions will include notification to the Central Controller, audio and/or visual indication at the device, adjusting the power output of the neighboring RFSDs, adjusting the antenna directivity and radiation patterns, and adopting a low risk approach of blocking all suspicious packets. The compromise is made in favor of security over efficiency. 
     RFSD 
       FIG. 8  provides a block diagram of a single channel RFSD, suited for IEEE 802.11 a/b/g/ protocols. The preferred embodiment of the RFSD will include transmit antenna  801  and receive antenna  802 ; multiple radios  803 , one or more radio direction finding (RDF) units  805  and controlled with a micro controller  806 . The radios  803  will be selected depending on the protocol of interest. 
     The RDF unit  805  is a signal analyzer that will compare two signals for strength and time of arrival and is also controlled by the micro controller  806 . To account for the differences in the electronics in the multiple paths from the antenna to the RDF unit  805 , a calibration will be done as a part of the “self-tuning” to generate and store an offset value to be applied during a real measurement. The Antenna steering unit  802 - 804  may be a phased may antenna control, or a simple antenna switch to transmit with another antenna present in the RFSD, or a physical antenna rotator, or a combination thereof. Multiple channel coverage will be achieved by replication of the above-mentioned architecture or by multiplexing across the channels. 
     Sanitized Wireless Zone (Dagger) 
     A direct effect of turning the transmitting antennas to point in the same direction as that of the receiving antennas and/or reversing the receiving antennas as the transmitting antennas, enables the RFSD to be used to “sanitize” a Defined Space where a specified type of packet switching digital communication wireless network will be disabled.  FIG. 11  describes one of the possible applications. The two transceivers  1105  and  1106  in  FIG. 11  attempt to establish communication, the wireless protocol handshake never completes successfully, as the RFSD destroys all packets  1111 - 1112  that it sees originating from within the “Sanitized Space”. The outside network, comprised of AP  1101  and wireless device  1102 , also never sees the handshake that is trying to take place inside. The insiders, however, will see all the wireless traffic that is happening outside the “Defined Space”. 
     Cloak and Dagger Application 
     The use of the RFSDs in both possible manifestations, i.e., cloaking packets leaking out from a secure space perimeter or cloaking packets within a secure space perimeter, allows the creation of sanitized, open access and secure zones. 
     Reverse Cloak Application 
     Reversing the Receiving and Transmitting Antennas on the RFSDs, results in the outside wireless networks being hidden from view of the insiders. 
     Forward and Reverse Cloaking Application 
     Using the combination of the reversed Cloak and the regular Cloak, creates a system where not only the inside wireless network is hidden from the outsiders, but the outside wireless network is also not seen by the insiders. 
     Redundancy 
     Redundancy is applied in two forms, one is within the RFSD by having backup Transmitting and Receiving systems, which can be used either under extreme unexpected load conditions and or environment changes or whenever the RFSD decides that these backup units need to be kicked in as well for additional security, or when one of the Tx/Rx chains fails/partially fails. 
     The other form of redundancy is by adding additional devices on the Secured Space, as shown in an example in  FIG. 7 . 
     Battery Backup 
     Two levels of battery backups are provided in the RFSD, one to ensure continued service during power failures where the internal wireless network is still functioning. As the battery power is limited, the preferred way is to power the Cloaking system with the same power grid/circuit as the internal wireless network to be secured. Here again the power will be most conveniently delivered using Power Over Ethernet (POE) or slightly modified POE for higher power rating. The second level of the battery backup is for the controllers, to have enough time to perform an elegant shutdown. 
     Reverse Engineering Proofing 
     Reverse engineering causes a huge impact not only on individual companies, but economically in general, as well. In order to discourage these malpractices by people or companies with ulterior motives, a well thought out “Self Destruct Mechanism” has been designed to put inside the RFSDs. 
     At the first level, stolen/lost RFSDs are useless without the authorization of the Central Controller. Each RFSD and Central Controller will be hard-coded, with a GUID like identification and each RFSD is further tied with a Central Controller, discouraging malicious use of the RFSDs. For special purposes an override mode will exist that will let the RFSD function without the Central Controller as well. 
     At the second level, any attempt to open the RFSD without a special electronic key (RFSD Key), will result in burning out most of the critical circuitry including some of the PCB tracks with minimum visual damage. This is done with critically placed fuses across the boards to blow up the critical components; this power is derived from the battery backup and capacitors. 
     The RFSD Key will be a mix of unpublished sequence delivered using IR/RF and proximity switches and receive an ACK/NACK confirmation back from the lock inside the RFSD. The RFSD Key distribution will be limited to manufacturing only and not to the field, except with prior approval, thereby discouraging stealing/copying of the key. 
     Alternate Access to RFSD 
     As it is possible that the RFSDs may be mounted in difficult to reach places, and there may be times that direct access to the device is required to update/configure/run diagnostics an alternate method of communication is made available through an Infrared (IR) port. The other alternative to access the RFSDs will be via another piece of software that can hook up directly to the Ethernet cable coming out from the RFSD. 
     Physical Installation of the Cloaking System 
     There are lots of different scenarios that can apply to the Cloaking System deployment, of which some have been pictorially described in  FIG. 7 . The actual mounting of the RFSDs will be highly dependent on the type, shape and the surroundings of the “Space to be cloaked”, however a typical installation will be done just outside the building or on a pole mount similar to a security camera or such other device. 
     In some cases it may even be possible to mount the RFSDs on the inside of a building say on a window or other such opening, it may even be possible to do a “split install” in which case part of the device is inside the building connected to an Ethernet jack and power or a POE jack/device, and another part sits in a weather proofed enclosure just outside the wall, connected with a cable that has been drilled through the wall. All of this mounting will be done by following the guidelines of the building and the Federal and State codes for installing external devices on or near a building, electrically connecting the devices to inside the building. Similar Codes will be followed for mounting the RFSDs and passing cables in an outdoor setup as well. 
     Central Controller Description 
     The Central Controller (CC) is the control authority and holds knowledge of all other systems in place. As and when the RFSDs power up, they register themselves with the CC, the RFSDs can communicate with each other via the CC, or lookup another RFSD from CC and establish a direct contact with it. The CC is a piece of software running on a computer on the same network, where the RFSDs are connected. The communication between the RFSDs and the CC is done over a secure tunnel to discourage theft and misuse. This also allows deployment across insecure networks. There can be one or more CCs that collect the information from and send information to the RFSDs. Essentially the CC works on a distributed architecture, where each CC talks to a set of RFSDs and send the information to the others as well. This architecture allows for redundancy, fail-safe operation and load balancing. 
     The User Interface (UI) in the CC is used for defining the space preferably with the use of a map of the space being cloaked; this information is then used for tuning the definition of the space. The CC collects the telemetry data from the RFSDs to monitor its health and statistics, to be displayed on a UI and/or stored for generating reports. The CC is also used as a single point software upgrade for one or more RFS devices. 
     The CC will also have SNMP interfaces available so that the Blue Leaf system can be monitored/administered using third party network management software, e.g., IBM Tivoli or HP OpenView. 
     An API will be provided for the CC that will allow installations or companies using proprietary network management solutions, to integrate this system into their solution, so that the CC&#39;s UI need not be used. 
     Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.