Abstract:
A telephony security system and method for controlling and logging access between an enterprise&#39;send-user stations at a plurality of customer sites and their respective circuits into the public switched telephone network (PSTN). The system and method includes a discrete line sensor within the customer sites for determining a call type of the call, and taking actions on the call based on predetermined security rules.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of Ser. No. 09/210,347, now U.S. Pat. No. 6,249,575 entitled TELEPHONY SECURITY SYSTEM filed Dec. 11, 1998, to the same assignee. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to telecommunications access control systems and more particularly, to a system and method which permits an in-line device to power-up and assume control of calls. 
     BACKGROUND OF THE INVENTION 
     A telecommunication firewall, such as the device described in U.S. Pat. No. 6,249,575 entitled TELEPHONY SECURITY SYSTEM is a recently developed device that protects an organization&#39;sdata network from access via telephony resources. Rogue modems installed without the knowledge or authorization of an organization&#39;IT personnel make an organization&#39;sdata network vulnerable to access by unscrupulous persons—both inside and outside the organization—via the Public Switched Telephone Network (PSTN). For example, an incoming modem call to an extension dedicated for only voice or fax use is indicative of a possible hacking attempt or of a rogue modem installed on the extension. Similarly, an outgoing modem call from an extension dedicated for only voice or fax use is indicative of a rogue modem and possible unauthorized activity within the private network. A telecommunications a firewall monitors incoming and outgoing calls via line sensors installed on trunks between the Central Office (CO) and the Private Branch exchange (PBX). The line sensor operates in a continuous loop, examining the data stream and determining call attributes (such as call source, destination and call content-type) as the data stream passes through the line sensor. In accordance with a user defined security policy, the line sensor autonomously denies violating calls and notifies IT personnel for appropriate follow-up. 
     Once installed, the line sensor signal receiving and transmitting circuitry is in-line with the trunk. When the line sensor switches on-line, it electrically receives and digitally regenerates the data traveling in both the transmit side and the receive side of each communication channel. In order to enforce the security policy, the line sensor must assume control of the data stream on each channel. If the trunk uses Channel Associated Signaling (CAS), gaining control of the call entails gaining control of the A/B bits transmitted between the CO and PBX. CAS uses specific bits of specific subframes to convey line state information that is analogous to “on-hook” and “off-hook”. Depending on the protocol used, a bit value of one generally corresponds to off-hook or “loop current flowing”, and a bit value of zero generally corresponds to on-hook or “no loop current”. It is highly desirous that the line sensor achieves control of the A/B bits in a manner that will not disrupt ongoing A&amp;B signaling, nor confuse the CO or PBX as to the line state, thereby inadvertently causing the call to be dropped. 
     Unfortunately, when the line sensor comes on-line, the state of the calls on each channel of the trunk is unknown. It is possible to preset the line sensor to transmit a default set of A/B bit values on each channel, but it is difficult to anticipate what the line state on each channel will actually be when the line sensor comes on-line. Calls would be disrupted on any channel whose A/B bit values did not correspond with the present default set of A/B bit values transmitted by the line sensor. It is inevitable that preset default values will be incorrect on some channels, thereby resulting in some percentage of disrupted calls and user inconvenience. 
     Therefore, what is needed is a system and method whereby an in-line device powers-up and assumes control of calls on a trunk without disrupting ongoing call activity. 
     SUMMARY OF THE INVENTION 
     The present invention, accordingly, is a system and method that allows an in-line device to step into the data stream of a communication channel and assume control of the data on a channel in a phased and progressive transition of its hardware and software in a manner so as to be transparent to both the CO and the PBX, and thereby avoid disruption of ongoing call activity. 
     To this end, in the preferred embodiment, the telecommunications firewall line sensor is installed in-line on the PBX side of the demarcation line. When the line sensor is off-line, all data in each channel of the trunk passes “untouched” through the line sensor so that normal call activity is not affected. When the line sensor switches on-line, the line sensor intercepts and digitally regenerates the data traveling between the CO and PBX. At this time, the line sensor determines the line state (A/B bit value) of each channel on the trunk. As the line state for each channel is determined, the line sensor reconfigures itself and overwrites the A/B bits in the received data with identical A/B bit values in the transmitted data, thereby successfully gaining control of the A/B bits transmitted. 
     Once the line sensor establishes control over the A/B bits, the line sensor is now capable of either overwriting the transmitted data with identical A/B bits, or of overwriting the transmitted data with altered the A/B bits, whichever is required to enforce the security policy. In other words, if the security policy allows a call, the line sensor overwrites the A/B bits with identical bit values and the regenerated data is identical to the data received. If the line sensor determines a call is in violation of the security policy and the call is to be denied, the line sensor regenerates the received data, but overwrites the A/B bits with bits that will signal to the CO and PBX that the call has ended, thereby terminating the call. 
     A technical advantage achieves with the invention is the ability for an in-line device to autonomously switch on-line and assume control of ongoing communications on a trunk without disrupting call activity, 
    
    
     Therefore, in accordance with the previous summary, objects, features and advantages of the present invention will become apparent to one skilled in the art from the subsequent description and the appended claims taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of an exemplary telecommunications firewall; 
     FIG. 2 illustrates a schematic block diagram of the preferred embodiment of the present invention. 
     FIG. 3 is a flow diagram illustrating the phased and progressive process of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention can be described with several examples given below. It is understood, however, that the examples below are not necessarily limitations to the present invention, but are used to describe typical embodiments of operation. 
     FIG. 1 is a schematic block diagram of an exemplary telecommunications firewall, similar to one implemented as shown and described in U.S. Pat. No. 6,249,575, comprising at least one line sensor  100 , a firewall client  102 , and a firewall management server  104 , all electrically connected by a Local Area Network (LAN), a Wide Area Network (WAN) or the Internet for interaction as described below. 
     The firewall client  102  is the point of user interface whereby the user designs and implements a security policy. The user creates rules that define which calls the line sensor  100  will allow, deny, or otherwise manipulate. The firewall management server  104  receives the security policy from the firewall client  102  and pushes a copy of the security policy to the line sensor  100 . The line sensor  100  monitors incoming and outgoing calls, determines call attributes, and allows, denies, or otherwise manipulates each call in accordance with the security policy. 
     In this embodiment, the line sensor  100  is installed in-series on a trunk  106  that uses Robbed-Bit Signaling (RBS) or some form of CAS. The line sensor  100  is located on the user&#39;s side of a demarcation line  108 , with interfaces to a Central Office (CO) switch  110  and a Public Branch exchange (PBX)  112 . 
     Also in FIG. 1, numerals  114 ,  116 , and  118  designate end-user stations  120 , representing as examples, one or more modems  114 , fax machines  116 , and telephones  118  which may send or receive calls over the trunk  106 . The modems  114  may be connected to a desktop or portable personal computer. Individual extensions  122  connect each of the stations  120  to the PBX  112 . 
     Now referring to FIG. 2, for the purposes of this invention, the line sensor  100  consists of relays  202  and  204 , transceivers  206  and  208 , and a CPU  210 . The relays  202  and  204  route the data stream through the line sensor  100 . The transceivers  206  and  208  observe and send copies of the A/B bit values in received data to the CPU  210 , digitally regenerate received data, and insert appropriate A/B bit values into the transmitted data stream. The CPU  210  executes software that switches the relays, configures the transmitting transceiver, and generates the appropriate A/B bit values for insertion into the transmitted data stream, thus controlling calls in accordance with the security policy. 
     In the preferred embodiment shown in FIG. 2, when the line sensor  100  is in the off-line mode (such as when the sensor is first installed, powered-off, reset, etc.), the relays  202  and  204  are in the Normally Closed (NC) position and allow the data stream on each channel to pass through the line sensor “untouched” via a default pathway  212  and  214 . 
     FIG. 3 illustrates a process  300  whereby the state of the line sensor  100  hardware and software transitions in a phased and progressive manner to enter the data stream on each channel of the trunk  106  and assume control of each call without disrupting ongoing call activity. In step  302 , the line sensor  100  is in the default off-line mode. The relays  202  and  204  are in the Normally Closed (NC) position when the line sensor is in the default off-line mode, so the data stream on each channel of the trunk  106  passes through the line sensor  100  “untouched” via a default pathway  212  and  214 . Phase I, neither the transceivers  206  and  208 , nor the CPU  210  have access to the data stream. 
     During Phase II and III, the receiving transceiver (RT) and transmitting transceiver (TT) digitally regenerate the data, including the A/B bit values, thus allowing the data stream to pass “unaltered” through the line sensor  100 . Phase II (step  304 - 314 ), begins when the CPU  210  asserts an “on-line” command  216  in step  304 . The relays  202  and  204  switch to the Normally Open (NO) position and route the data stream for each channel through the transceivers  206  and  208 , via a pathway  218  and  220 , as described in step  306 . The TT regenerates the data, including the A/B bit values exactly as received by the RT. In step  308 - 322 , one channel at a time, (where the letter i represents, for this example, one of the 24 channels on a T 1  trunk), a process loop is applied. In step  312 , the RT observes the A/B signaling bits on channel i and sends a copy of the bits to the CPU  210 , in the form of an observed A/B bit value  222 . 
     Phase III (step  314 - 322 ), begins as the CPU  210  stores the observed A/B bit value  222  of channel i in memory, in step  314 . In step  316 , the CPU  210  configures the TT to receive CPU-provided signaling bits and to insert those bits into the regenerated data on channel i. In step  318 , the CPU  210  sends to the TT, a CPU-provided A/B bit value  224 , which is identical to the RT-observed A/B bit value  222 . In step  320 , the TT inserts the CPU-provided A/B bit value  224  into the data stream on channel i and thereby overwrites the A/B bit value in the data stream coming from the RT. The line sensor repeats step  310 - 322  as the TT inserts the channel-specific CPU-provided A/B bit value  224  into the data stream on each channel i. Since the A/B bit value  224  the TT inserts is identical to the observed A/B bit value  222  sent to the CPU  210  by the RT in this phase, ongoing call activity is not disrupted. 
     Phase IV (step  324 - 338 ), is outside the scope of this invention, is now discussed to further demonstrate the purpose and value of this invention. Having successfully entered the data stream and progressively assumed control of call activity in Phase I-III, the line sensor  100  is able to exert its control to deny inbound and outbound calls, as well as terminate calls in-progress in accordance with the user-defined security policy by overwriting the A/B bit values as necessary. 
     In step  324 , the RT continues to monitor the signaling information on each channel, and sends a copy of any change in the observed state to the CPU  210  as long as the line sensor  100  remains in the on-line mode. If the A/B bit value changes, the RT sends a new observed A/B bit value  222  to the CPU  210  in step  326 . The CPU stores the new state in step  328  and immediately sends a corresponding and identical CPU-provided A/B bit value  224  to the TT to insert into the data stream in step  330 . If the call is to be allowed, the CPU-provided A/B bit value  224  corresponds to the observed A/B bit value  222 . Until it receives new A/B bit values from the CPU  210 , the TT inserts the most recently provided A/B bit values. 
     If the call is determined to violate the security policy in step  334 , the CPU provides to the TT, the new A/B bit value  224  that correspond to a “hang up” state, in step  336 . In step  338 , the TT overwrites the A/B bits in the data it regenerates with the CPU-provided A/B bit value  224  that correspond to a “hang up” state, thereby terminating the call. 
     It is understood that the present invention can take many forms and embodiments. The embodiments shown herein are intended to illustrate rather than to limit the invention, it being appreciated that variations may be made without departing from the spirit of the scope of the invention. For example, this invention can be used for a plurality of telecommunications trunk-types. Some examples are T 1 , E 1  and J 1  that use Channel Associated Signaling (CAS) and Robbed Bit Signaling (RBS). The algorithms and process functions performed by the invention may be organized into any number of different modules or computer programs for operation on one or more processors or workstations separate from the line sensor. 
     It is understood that several modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.