Abstract:
An information transmission system comprising a conductor operable to carry a desired information signal. A first tube substantially surrounds the conductor and a second tube substantially surrounds the first tube to define a substantially fluid-tight chamber therebetween. In another aspect, the invention provides an information transmission system suited to transmit information between a first electronic device and a second electronic device located a distance from the first electronic device. The system includes an information transmission line that connects to the first electronic device and the second electronic device. A conduit surrounds at least a portion of the information transmission line. The conduit defines a substantially fluid-tight chamber. A quantity of fluid is disposed within the chamber and a sensor is positioned to measure a parameter of the quantity of fluid. An indicator is operable to signal a breach condition in response to the measured parameter.

Description:
The invention was conceived or reduced to practice in the performance of work under U.S. Government Contract # N00019-93-C-0196 awarded by the U.S. Navy. 

   BACKGROUND 
   The present invention relates generally to information transmission systems. More particularly, the present invention relates to a system and method for detecting tampering with an information transmission system. 
   Information transmission, such as transmission between two computers in an office building, is often accomplished by sending the desired information through an information transmission line that interconnects the two computers. However, it is often required that this information be protected from surveillance or intrusion. If the entire building, or complex of buildings, is secured to a suitable level, the transmission of information presents fewer problems. However, as is often the case, a building may include different levels of security. As such, an information transmission may be required to travel from one room having a high level of security to another room having a high level of security by passing through a relatively low security area. In these situations, it is necessary to secure the information or the information transmission line as it passes through the low security area. 
   To secure the information, some facilities employ information encryption. The information is encrypted before it is transmitted and is decrypted at the receiving point. However, encryption systems can be expensive and complicated to operate, and tends to slow the information transmission. 
   In other situations, the information transmission lines are secured using sensors. The sensors are positioned adjacent the information transmission lines to detect any sort of tampering that may occur. Typical sensors include line-of-site long-range beam sensors, infrared sensors, and/or vibration wire. These sensors function best when they are designed as part of the building. However, when retrofitting them into an existing building, problems arise that make them difficult and costly to install and maintain. In addition, many of these systems require a straight, unobstructed path between the higher security areas to function properly. 
   SUMMARY 
   The present invention generally provides an information transmission system comprising a conductor operable to carry a desired information signal. A first tube substantially surrounds the conductor and a second tube substantially surrounds the first tube to define a substantially fluid-tight chamber therebetween. 
   In another aspect, the invention generally provides an information transmission system suited to transmit information between a first electronic device and a second electronic device located a distance from the first electronic device. The system includes an information transmission line that connects the first electronic device and the second electronic device. A conduit surrounds at least a portion of the information transmission line. The conduit defines a substantially fluid-tight chamber. A quantity of fluid is disposed within the chamber and a sensor is positioned to measure a parameter of the quantity of fluid. An indicator is operable to signal a breach condition in response to the measured parameter. 
   In still another aspect, the present invention generally provides a method of detecting tampering or other breach condition of an information transmission line. The method includes surrounding at least a portion of the information transmission line with a conduit and sealing the conduit to define a substantially fluid-tight chamber. The method also includes providing a fluid to the fluid-tight chamber and monitoring the pressure of the fluid within the fluid-tight chamber. The method further includes signaling a breach condition when the pressure within the fluid-tight chamber changes more than a predetermined magnitude. 
   Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The detailed description particularly refers to the accompanying figures in which: 
       FIG. 1  is a schematic illustration of an information transmission system including end seals and an information transmission line; 
       FIG. 2  is a perspective view of an end of the information transmission system of  FIG. 1 ; 
       FIG. 3  is a partially broken away view of the information transmission system of  FIG. 1 ; 
       FIG. 4  is a perspective view of the end seal of  FIG. 1 ; 
       FIG. 5  is a section view of the end seal of  FIG. 4 ; and 
       FIG. 6  is a schematic illustration of an alarm system including the information transmission system of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Before describing an embodiment of the invention in detail, a brief discussion of building security is necessary. Most office or factory buildings, or complex of buildings, include some level of security. In most cases, this security is low, comprising mainly locks (electronic or mechanical) on the doors or security guards or receptionists at the entrance. However, some industries (e.g., computer chip developers, software developers, toy manufactures, and the like) often require additional security to inhibit or prevent unwanted intrusion. To that end, buildings occupied by these industries often include varying levels, or layers of security. For example, one building may allow entry of any person with an ID badge but may limit the access of that person to only certain areas. Thus, a single building may include two or more security levels, with one security level being lower than the other security level. The lower security level may still be quite high when compared to typical office buildings. For example, the low security level may be classified as “Low Security” thus requiring significant security, while the high security level may be “Restricted Access” thus requiring security precautions in addition to those provided in the lower security area. 
   The present invention allows for the secure and relatively inexpensive transmission of information from one higher security area to another higher security area through a lower security area. However, the invention should not be limited to any particular security level, as it will function to transmit information from one room to another no matter the security level in the rooms or between the rooms. Thus, while the invention is described as transmitting information from one high security room to another high security room via a low security area, these terms are not meant to categorize the actual level of security employed. Rather, they indicate a relative difference in security and are used for exemplary purposes only. In addition, the invention is described as extending between two rooms in a building. However, the invention could be used to connect rooms in different buildings if desired. 
   With reference to  FIG. 1 , a portion of a building  10  including multiple levels of security is illustrated schematically. The building includes a first area  15  or room and a second area  20  or room separated by a third area  25 . The first and second areas  15 ,  20  contain electronic devices  30  such as computers or other information transmission or storage devices. An information transmission line  35  extends between the first area  15  and the second area  20  to interconnect the electronic devices  30 . In the construction illustrated in  FIG. 1 , the information transmission line  35  passes through a space beneath a false floor  40 . However, other constructions may route the information transmission line  35  through walls or a ceiling if that is more convenient. 
   In most applications, the first area  15  and the second area  20  are high security areas (e.g., laboratories, offices, engineering areas, and the like), while the third area  25  is a low security area (e.g., hallways, conference rooms, cafeterias, and the like). As such, the information transmission line  35  passes from high security to low security and back to high security. To maintain the security level of the information, the portion of the information transmission line  35  within the low security area is enclosed in a conduit  45 . 
   The conduit  45  includes a first or inner tube  50 , a second or outer tube  55  that surrounds the inner tube  50 , and an optional coating  60  that surrounds the outer tube  55  as illustrated in  FIG. 2 . In some constructions, the inner tube  50  and the outer tube  55  are formed from corrugated copper. However, other constructions may employ non-corrugated tube for one or both of the inner tube  50  and the outer tube  55 . In addition, other tube materials such as plastic, composite, and the like can be used with copper and other metals being preferred. The use of copper, as well as other metals, as the material to manufacture the inner tube  50  and the outer tube  55  further enhances the information protection capability of the present invention. The copper at least partially shields any electromagnetic emissions emanating from the information transmission line  35 . This shielding inhibits the passive monitoring of the information as it is transmitted. 
   The coating  60  protects the outer tube  55  from abrasion or damage that may occur during the installation and/or operation of the conduit  45 . In addition, the coating  60  protects the outer tube  55  from corrosion and other environmental damage that may impair the function of the conduit  45  over time. 
   The inner tube  50  defines a conductor space  65  sized to allow for the passage of the information transmission line  35 . In addition, the tubes  50 ,  55  cooperate to define a portion of an annular chamber  70  that extends substantially the entire length of the conduit  45 . 
   A spacer piece  75  extends the length of the inner and outer tubes  50 ,  55  in a helix pattern such that it periodically contacts both the inner tube  50  and the outer tube  55 . The spacer  75  does not form a seal between the inner tube  50  and the outer tube  55 . Rather, the spacer  75  maintains the desired gap between the inner tube  50  and the outer tube  55  and maintains the inner tube  50  in a substantially centered position within the outer tube  55 . The spacer  75  is made from any suitable material with TEFLON or another plastic being preferred. The spacer  75  assures that the information transmission line  35  is not in direct physical contact (metal to metal contact) with the outer tube  55 . This additional isolation may reduce the likelihood of passive monitoring of the signal being transmitted via the information transmission line  35 . While preferred constructions employ the spacer  75  as illustrated in  FIGS. 2 and 3 , other constructions may function without the spacer  75  or with a different spacer (e.g., rubber annular washers and the like). 
   An end cap  80  is positioned at either end of the inner tube  50  and outer tube  55  within the first area  15  and the second area  20  to complete the conduit  45  as shown in  FIG. 1 . A conduit  45  similar to that just described is sold by Vacuum Barrier Corporation of Woburn, Mass. under the trade name SEMIFLEX. 
   The end caps  80 , illustrated in  FIGS. 4 and 5 , include an open end  85  that provides for the passage of conductors through the conduit  45  and an attached end  90  that attaches to the inner tube  50  and the outer tube  55 . Each of the end caps  80  includes an inner wall  95  and an outer wall  100  that attach to one another near the open end  85  to define the open ends  85  of each end cap  80 . The inner wall  95  and the outer wall  100  are separated from each other at the attached end  90  of the end cap  80 . Thus, the inner and outer walls  95 ,  100  cooperate to define an annular space  105  that terminates adjacent the open end  85 . 
   The inner walls  95  of the end caps  80  attach to either end of the inner tube  50  and the outer walls  100  attach to either end of the outer tube  55  to complete the conduit  45 . The walls  95 ,  100  and tubes  50 ,  55  can be attached using any suitable means (e.g., brazing, soldering, adhesive, and the like) with welding being preferred. With the end caps  80  attached, the inner walls  95  cooperate with the inner tube  50  to complete the conductor space  65 . The annular spaces  105  seal the ends of the chamber  70  to complete the chamber  70 . Thus, the chamber  70  surrounds all but the open ends of the conductor space  65 , which are preferably disposed within the high security areas  15 ,  20 . 
   One or both of the end caps  80  include a supply line  110  that is in fluid communication with the chamber  70 . The supply line  110  connects to a release/fill valve  115  (shown in  FIG. 6 ) that provides for fluid communication between a source of high-pressure air (e.g., compressor, shop air, etc.) and the chamber  70 . The valve  115  can be configured to admit high-pressure air into the chamber  70 , to vent high-pressure air from the chamber  70 , or to seal the supply line  110  and the chamber  70 . In addition, the supply line  110  provides for fluid communication between the chamber  70  and a sensor  120  that measures a parameter such as the pressure within the chamber  70 . It should be noted that supply lines  110  and sensor  120  could be positioned anywhere desired. Preferably, the sensor  120  is located within the high security area along with one of the first and second electronic devices. However, the invention should not be limited to supply lines  110  and sensors  120  positioned in the end caps  80  or the high security areas alone. 
   The sensor  120  provides a signal corresponding to the measured pressure to an alarm system  125 . The alarm system  125  signals a breach condition when the pressure falls below or exceeds a predetermined value. As used here, a “breach condition” is any condition that results in a sufficient pressure change to be sensed by a sensor regardless of the cause. “Breach condition” includes but is not limited to pressure changes caused by tampering, intrusions, accidental breakage, and deterioration due to aging or environmental causes. The alarm system  125  may also trigger an audible or visual alarm in addition to initiating other steps to secure the information transmission line  35  (e.g., terminating all information transmission). One sensor  120  suited to use with the present invention is the Modus Pressure Alarm Control and Digital Pressure Gage as sold by Modus Instruments Inc., of Clinton, Mass. 
   To use the present invention, the conduit  45  is first installed between two or more devices  30 , such as computers as illustrated in  FIG. 1 . When installed, the portion of the information transmission lines  35  disposed in the low security area  25  is completely surrounded by the chamber  70 . The only exposed information transmission lines  35  extend from the open ends  85 , which are preferably disposed within the high security areas  15 ,  20 . Thus, to breach the information transmission line  35  in the low security area  25 , one must first penetrate the chamber  70 . 
   The chamber  70  is charged, or pressurized with a fluid, such as air to a pressure sufficiently above or below atmospheric pressure so that the sensors may detect a breach condition. Before proceeding, it should be noted that pressure levels can be measured as gauge pressures or absolute pressures. The pressure levels described herein are gauge pressures. However, one of ordinary skill in the art will realize that the sensors will function using either gauge pressure or absolute pressure. While many different pressure levels will function, a pressure level in excess of about 20 pounds per square inch gauge is preferred. In most constructions, an initial pressure of about 25 pounds per square inch gauge functions well, with higher or lower pressure (e.g., above 25 psig or below 20 psig) being suitable for different applications. The actual pressure used in each application is a function of many variables (e.g., sensor sensitivity, volume/length of the conduit, seal quality, temperature fluctuations, etc.). Present sensors  120  will detect a pressure drop or increase of 3 psi with few errors or nuisance alarms. More accurate sensors may allow for the accurate detection of a 1 psi pressure change or an even smaller pressure change. As such, the pressure values described herein can be modified based on the accuracy or sensitivity of the sensor. Likewise, the volume of the conduit  45  may necessitate changes in the pressure values. For example, a higher pressure may be desirable in a larger conduit  45  to assure that the pressure drops quickly in response to a breach. In addition, monitoring for a smaller pressure drop may be desirable in large volume conduits  45  to assure that any tampering is detected quickly. 
   Air is initially supplied to the chamber  70  via the supply line  110  that feeds into the chamber  70 . The supply line  110  is then closed to substantially seal the chamber  70 . The pressure within the chamber  70  is then periodically or continuously monitored. 
   If the pressure changes a predetermined amount, typically in excess of about 3 pounds per square inch, the alarm system  125  will signal a breach condition. In preferred constructions, a pressure drop of about 5 pounds per square inch triggers the breach condition. In another construction, the sensor  120  measures the rate of pressure change rather than the actual pressure drop to detect tampering and trigger the breach condition. 
   In yet another construction, a second sensor measures a temperature, such as the fluid temperature within the chamber  70 . The alarm system uses the measured temperature to compensate for pressure changes caused by local temperature changes. For example, a temperature change may cause a pressure drop in the conduit of 1 psi. Without temperature compensation, another 2 psi drop would be all that is required to trigger a breach condition. By compensating for the temperature change, the system is able to maintain the pressure drop required to trigger the breach condition at a desired value (e.g., 3 psi), thus reducing nuisance alarms. 
   Once a breach condition is signaled, the alarm system  125  may initiate an alarm. The alarm may be audible, visual, or both. In addition, the alarm system  125  may alert security and/or cut off information flow through the information transmission line  35 . As one of ordinary skill will realize, the reaction of the alarm system  125  to the breach condition may vary greatly depending on the particular application. 
   While the present invention has been described as using high-pressure air to fill the chamber  70 , one of ordinary skill will realize that other gasses could be used if desired. In addition, rather than using high-pressure air, a partial vacuum could be employed. In constructions that employ a partial vacuum, the sensor  120  would monitor the pressure within the chamber  70  with an increase in pressure indicating tampering. 
   Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.