Abstract:
A method and system for using watermarks in communication systems is disclosed. Watermarks are typically small amounts of auxiliary data embedded in a cover signal. The cover signal is the primary communication signal, and may be binary bits, multi valued symbols, analog waveforms, or any other type of primary communication signal. Security strength indication, location tracking, intrusion detection and transmission of non-security information using watermarks are disclosed, along with a system for managing watermarks.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application claims the benefit of U.S. Provisional application No. 60/545,678, filed Feb. 18, 2004, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates generally to communication systems. More specifically, the present invention is directed to using watermarks in communication systems.  
       BACKGROUND  
       [0003]     Communication systems provide a large and growing number of convenient communication services, and have become a pervasive part of modern life. Such communications will continue to grow in popularity and capability, driven by such innovations as the availability of high-speed wired and wireless Internet access, rapidly developing wireless devices, growing popularity of global positioning system (GPS) applications, etc. As the use of these technologies continues to grow, however, currently apparent deficiencies and susceptibilities are likely to become more troublesome, while others are likely to arise. For example, valuable consumer data can readily be extracted from many sources where the consumers have little or no control over the extraction of data which they may have voluntarily provided to a third party for a legitimate purpose. With no control mechanisms, such extraction of consumer data may cause users to view their communications as risky and feel as though the risks are invisible and/or impossible to control.  
         [0004]     The issues outlined above may generally be categorized as pertaining to “trust,” “rights,” “identity,” “privacy” and “security,” collectively referred to as TRIPS. “Trust” refers to the assurance that the entity to which information being communicated in these systems is dependable in specific situations. To illustrate, a user may want to know that a communication was sent to it from a trusted source, using trusted communication nodes. The user in an ad-hoc network may have no knowledge that the communication was transferred over a hacker&#39;s device with packet sniffing software. Additionally, with the use of tunneling, intermediate nodes transferring the communication may be transparent to the user.  
         [0005]     “Rights” (or “rights management”) refers to the control of access to data or devices. To illustrate, a user may have limited rights in a communication system, and is therefore restricted to a subset of available services while operating within the system. However, if that user colludes (knowingly or unknowingly) with a second node having superior rights, that user may gain rights above those that the user is allowed, and thereby gain access to system resources not otherwise available to him.  
         [0006]     “Identity” refers to the control of information associated with the identity of a user. To illustrate, a rogue device may attempt to access a network by pretending to be an authorized user of the network, by using that authorized user&#39;s identity.  
         [0007]     “Privacy” refers to ensuring the privacy of the individual, the data and the context. To illustrate, a user may not want others to know which web sites the user visits. Or, a user may want to keep specific communicated information private, such as financial or medical information, etc.  
         [0008]     “Security” refers to the security of the data and context, such as preventing an unauthorized individual access to a user&#39;s information.  
         [0009]     To reduce the susceptibility of communication systems to unauthorized or unintended access to data residing or being communicated on them, techniques such as wired equivalent privacy (WEP), Wi-Fi Protected Access (WPA), Extensible Authentication Protocol (EAP) and GSM based encryption are used. Although these techniques provide some protection, they are still susceptible to trust, rights, identity, privacy and security issues. To illustrate, although a particular wireless communication node may have the correct WEP keys to communicate with a wireless user, that user may not know whether he/she can “trust” that node.  
         [0010]     Additionally, authentication of the user using the keys required by these systems typically occurs at higher layers of the communication stack. Accordingly, even when these controls are in place, a rogue wireless user or hacker may have some (although limited) access to the communication stack. This access creates vulnerabilities, such as to denial of service attacks, among others.  
         [0011]     A Watermark (or digital watermark) is typically a small amount of auxiliary data that is embedded in a cover signal, which is the primary communication signal. The cover signal may be binary bits or multi valued symbols or analog waveforms involved in the primary communication. Since the watermark is embedded in the primary communication signal, it is desirable to explore how watermarks may be used to protect communication systems, in all aspects described above.  
       SUMMARY  
       [0012]     The present invention is a method and system for using watermarks in communication systems. Watermarks are typically small amounts of auxiliary data embedded in a cover signal. The cover signal is the primary communication signal, and may be binary bits, multi valued symbols, analog waveforms, or any other type of primary communication signal. Security strength indication, location tracking, intrusion detection and transmission of non-security information using watermarks are disclosed, along with a system for managing watermarks.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a wireless communication system wherein WTRUs are provided with a security strength indicator providing an indication of the level of protection provided within the coverage area in which the WTRU is operating.  
         [0014]      FIG. 2A  is a WTRU having a screen wherein a security strength indicator is displayed.  
         [0015]      FIGS. 2B and 2C  are graphical representations of a security strength indicator.  
         [0016]      FIG. 3  is a coverage area of a base station of a wireless communication system in accordance with the present invention.  
         [0017]      FIG. 4  is a WTRU and base station configured for managing the use of watermarks.  
         [0018]      FIG. 5  is a wireless communication system wherein watermarks and sensors are used for intrusion detection in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     As used herein, a wireless transmit/receive unit (WTRU) includes but is not limited to a user equipment, mobile station, fixed or mobile subscriber unit, pager, station (STA) or any other type of device capable of operating in a wireless environment.  
         [0020]     As used herein, a base station (BS) includes but is not limited to a Node-B, site controller, access point or any other type of interfacing device in a wireless environment. When referred to hereinafter a transmit/receive unit (TRU) includes a WTRU, base station or a wired communication device.  
         [0021]     As used herein, watermarks include but are not limited to metadata, tokens, keys, signatures, or any other type of identifying information associated with data packets. The information may be derived directly from TRU specific information, or from or in conjunction with other information.  
         [0022]     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components.  
       Watermarking of Communications  
       [0023]     As used herein, watermarking can be broadly classified into two main categories; 1) watermarking of messages for security purposes, to thwart improper use of network resources or information; and 2) watermarking of messages for non-security purposes, such as to indicate context information, or to provide more efficient signaling or better control.  
         [0024]     With regard to security purposes, the different means of generating watermarks can be classified based on their security levels, complexity and cost of implementation. Depending on security needs, any of various levels of security can be implemented. In general, the security of a communications system can be multi-tiered, and the security parameters of higher network layers can be set using watermarks.  
         [0025]     The choice of stack for communication is preferably based on the physical level security (i.e. layers  1 - 7 ). The type of security at the different levels is varying based on the physical level. In one embodiment, networks may be deployed using physical security the way in which frequency, time slot, and code are used.  
         [0026]     The steps to address security issues can be generally categorized as follows: prepare for attempts to improperly use network resources or information; prevent such use (secure against and deter such use); detect; alert; contain and eliminate such use; and identify the improper user.  
         [0027]     Preparing for improper use relates to putting mechanisms in place to manage heightened potential risk of improper use. Similar to the profiling of individuals known or believed to have engaged in unsafe activities, and assessing and containing the potential risk of such individuals to airline travelers. A similar database for communication offenders can be established and managed. Watermarks can be used to identify offenders, and to indicate their appearance on the network; whereupon precautionary measures can be taken, such as increasing the network security level.  
         [0028]     Preventing improper use relates to securing a network against improper use, and deterring such use. With respect to securing a network, when the existence of a security risk on the network is detected, a security state can be broadcast to the network, similar to a terrorism threat level (red, orange, yellow), for example. The security state can be communicated by an AP or base station, which can initiate a change, up or down, in the amount of security enabled by the network and/or client devices.  
         [0029]     With respect to deterring improper use, indicators of security measures in place may be employed, for example. This is analogous to indicating the existence of a building security system against unauthorized entry by displaying a sign that such a security system is in use. The indicator can be controlled by watermarks, and can include the display of a logo or other indicator defining the currently applied security standard. Other protection indicators can include those associated with measures that a user can enable or disable.  
         [0030]     Another method to deter improper use of network resources and information is to provide an agent that periodically checks in on each user to see if everything looks normal. In this case, the average user is monitored to make sure all activity that affects him is conventional.  
         [0031]     Detection of improper use may be accomplished by implementation of an intrusion detection protocol, for example. Out of character behavior for individual network users can be detected and used to heighten security measures. For example, it can be determined through monitoring that a user normally uses network resources or information in some sort of a repeatable pattern or profile. If the user changes behavior in some significant and possibly risky way, this detection can enable additional security precautions, or trigger an authentication or re-authorization procedure.  
         [0032]     Another method to detect improper use is to place sensors on the network at various locations to continuously monitor user activity. Any transmissions without the proper watermarks, can trigger an intruder alert. This can be used to re-authenticate the users in the vicinity of the detecting sensor. The security level of the network can also be upgraded, and sensors may also be used to identify the location of the intruder.  
         [0033]     Another method to detect improper use of network resources and information is to provide an agent that sends a check-up to a user who appears to be engaging in uncharacteristic and/or risky activities. Such activity can either be detected at the AP (e.g., MAC address re-use); or detected through a “neighborhood watch” program where clients in the vicinity detect improper behavior.  
         [0034]     User monitoring can be accomplished in an office building or campus employing sensors in each room or at many locations. The RF range of the sensors can be limited, e.g., by transmitting at low power. The user equipment can be asked to relay beacons transmitted by the sensors, and the network can thereby track the user continuously.  
         [0035]     With respect to providing an alert to improper use, a security indicator on a device attached to a network, similar to a battery power level indicator, can be provided to indicate the type of activity the device is engaged in.  
         [0036]     With respect to containing improper use, e.g., by use of watermarks for repudiation, when a rogue transmitter is identified on a network, its identity can be broadcast to the other network users, and all devices can be directed to ignore the rogue transmitter&#39;s requests for the medium. In 802.11, this can be accomplished by ignoring any virtual carrier sense reports from the transmitter. This is less complicated than ignoring the physical carrier sense, since in that case the determination of the source is made at a higher layer. A broadcast of the currently identified threat can also indicate which network mechanisms should be protected better.  
         [0037]     With respect to eliminating improper use, in the event of a denial of service attack, all network devices can be instructed to begin packet-by-packet inspection for a specific TA in the packet header of 802.11 wherein detected packets can be ignored.  
         [0038]     To identify an improper user, watermarks can be used to indicate information about a user or device improperly using network resources or information. Watermarks can indicate, for example, context information such as physical or logical location, or device specific information such as a hardware identifier. Additional detail regarding the use of watermarking for security purposes is provided in the description of the Figures, which is hereinbelow.  
         [0039]     Referring now to using watermarks for non-security purposes, watermarks may be used for all types of non-security purposes including, for example, context, signaling, and control. A few examples are provided below.  
         [0040]     Comparison of a watermark between two and more devices can be used to determine the distance (physical and logical) between devices and used for a multitude of uses (location, intrusion detection, context awareness, routing, store and forwarding, power management, etc. . . . ). Header overhead can be reduced by using watermarks instead of MAC or IP information in a header. This can be useful where the capabilities of the network or of networked devices are limited, and it is critical to reduce the size of data packets or to conserve bandwidth.  
         [0041]     Watermarks can also be used to implement providing and accounting for different service levels to users in different service classes. For example, a user may want to ensure security or other special protections when less than desirable conditions exist in the network. Watermarking can be enabled as a function of a service plan. For example, in a CDMA system extra physical layer protections can be maintained on traffic only of a specific user class, invisible to the user. Only traffic of that class can run on those protected lanes of digital communication.  
         [0042]     Watermarks can also be used in an ad hoc fashion in social gatherings, to match likes and dislikes of people in the same vicinity. They can also be used as news broadcasters in an ad hoc fashion to distribute context information such as accident data, temperature data, etc. Additional detail regarding the use of watermarks for non-security purposes is provided in the description of the Figures, which is hereinbelow.  
       Security Strength Indication by Watermarks  
       [0043]     In a first embodiment of the present invention, a security strength indicator is provided to devices operating within a communication system. There are many different techniques for addressing TRIPS issues in communication systems. For example, specific techniques for addressing various TRIPS issues are described in U.S. patent application Ser. No. 10/996,493, filed on Nov. 23, 2004 (hereinafter the &#39;493 application), 11/035,174, filed on Jan. 13, 2005 (hereinafter the &#39;174 application), and 11/034,987, filed on Jan. 13, 2005 (hereinafter the &#39;987 application), each of which are incorporated by reference as if fully set forth herein. The various watermarking techniques may generally be classified based on the level of protection provided, complexity, and cost of implementation. The security strength indicator described herein quantifies the level of protection provided on a per base station basis based on the techniques being implemented by the particular base station and provides an indication to the WTRUs operating within the base station&#39;s coverage area of the level of protection provided in that coverage area.  
         [0044]     Referring now to  FIG. 1 , a wireless communication system  100  is shown. The wireless communication system  100  includes, in one embodiment of the present invention, a network controller  102 , a plurality of base stations  104 , and a plurality of WTRUs  106 . In a preferred embodiment of the invention, a security strength indicator is provided to or by each base station  104  in a wireless communication system  100 . The base station  104  communicates the security strength indicator to the WTRU&#39;s  106  operating within its coverage area.  
         [0045]     The security strength indicator is preferably generated on a per base station basis. This allows, for example, a particular security strength indicator to be provided for the WTRUs  106  operating within coverage area  108  while WTRUs  106  operating within coverage area  110  are provided with a different security strength indicator. This is useful in situations where coverage area  108  is, for example, a residential area wherein lower tier protection techniques are implemented and coverage area  110  is, for example, a military base wherein higher tier protection techniques are implemented. The security strength indicators may be broadcast from the base stations  104  to their respective WTRUs  106 . Alternatively, the security strength indicators may be transmitted as watermarks from the base stations  104  to their respective WTRUs  106 .  
         [0046]     The security strength indicators may be generated at a network controller  102  for each of the base stations  104 . In another embodiment, the base stations  104  may generate their own security strength indicators. In still another embodiment, the WTRUs may be configured to generate security strength indicators where they are operating in an ad-hoc network, for example. Or, the security strength indicator may be generated by the base stations  104  based on information reported to them by the WTRUs  106 .  
         [0047]     The security strength indicator is preferably generated dynamically in that it may be computed at predetermined intervals. In this manner, the security strength indicator may vary as a function of the state of the system  100 . For example, if an intruder is detected in say coverage area  108 , the security strength indicator may be upgraded or otherwise adjusted, as appropriate.  
         [0048]     The security strength indicator may be quantified as desired. For example, a coverage area in which 128 bit encryption is being used may have a higher security strength indication than a coverage area wherein 56 bit encryption is being used. Similarly, a coverage area wherein watermarking is implemented at lower layers (i.e. physical or RF layer) may have a higher security strength indication than a coverage area wherein watermarking is implemented at higher layers (i.e. application layer).  
         [0049]     The security strength indicator may be displayed on a WTRU  106  in any manner as desired. For example, reference is now made to  FIGS. 2A, 2B , and  2 C. In  FIG. 2A , a WTRU  106  having a screen  130  wherein a security strength indicator  132  is displayed. The security strength indicator can be anything sufficient to indicate a particular value among a range of values, e.g., a number in a range from a low number to a high number, such as the number 4 on a scale of 1 to 5 (not shown) or some type of graphic indicator. Or, color indicators can be used, for example, where green indicates good and tight security and red indicates loose or lax security, and yellow indicates an intermediate level of security. In such a scheme, white may represent an unknown, undetermined or unreported level of security.  FIG. 2B  is a first example of a graphical indicator indicating the equivalent of a security strength indicator value of four (4) wherein the indicator has a scale of one (1) to five (5), for example.  FIG. 2C  is a second example of a graphical indicator, also showing the equivalent of a security strength indicator value of four (4) on a scale of one (1) to five (5). Level zero (0) can represent an unknown, undetermined or unreported level of security.  
       Location Tracking Using Watermarks  
       [0050]     By way of explanation, a watermark is the insertion of metadata or other unique information into data transmitted between a transmitter and receiver for signaling and/or security purposes. Detailed descriptions of various watermarking techniques are provided in the &#39;493, &#39;174, and &#39;987 applications referenced above.  
         [0051]     Referring now to  FIG. 3 , a coverage area  302  of a base station  304  of a wireless communication system  300  in accordance with the present invention is shown. The system includes a plurality of WTRUs  306   1 ,  306   2 , and  306   n  operating within the coverage area  302 . Additionally, a plurality of sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318  are deployed throughout the coverage area  302 . The sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318  are preferably configured to transmit at a relatively low power so that the RF range of the sensors is appropriate in view of the number of sensors that are deployed in an area and the relative spacing between them.  
         [0052]     The sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318  are configured to periodically (or in response to a specific command) transmit an identifier to WTRUs within its RF range which is forwarded by the WTRUs as an embedded watermark to their respective base station for purposes of tracking the location of the WTRUs. In a preferred embodiment, the network is aware of the location of each sensor  308 ,  310 ,  312 ,  314 ,  316 ,  318  and the particular identifier that each sensor  308 ,  310 ,  312 ,  314 ,  316 ,  318  transmits. Therefore, based on the watermark that is received and the WTRU from which the watermark was received, the location of the WTRU may be computed.  
         [0053]     In one embodiment, WTRUs  306   1 ,  306   2 , and  306   n  authorized to operate within a coverage area  302  may simply be required to forward signals received from the sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318  to the base station  304  as embedded watermarks. In this embodiment, the WTRUs  306   1 ,  306   2 , and  306   n  may not even be aware of the watermarks and are simply operating as a conduit for transmission of the identifiers from the sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318  to the base station  304 .  
         [0054]     In another embodiment, however, the identifiers sent by the sensors may be encrypted, and the WTRUs  306   1 ,  306   2 , and  306   n  authorized to operate within a coverage area  302  may be provided with a key for extracting the identifiers. In this embodiment, WTRUs  306   1 ,  306   2 , and  306   n  authorized to operate within the coverage area  302  are provided with sufficient information to compute their location based on receipt of identifiers from the sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318 . In this embodiment, any WTRU, say WTRU  320 , who fails to provide its location information upon request may be an unauthorized WTRU attempting to operate in a restricted/controlled area. Alternatively, WTRU  320  may be an authorized user that simply needs to be re-authenticated or a new user that needs to be authenticated.  
       Transmission Of Non-Security Information Using Watermarks  
       [0055]     Continuing to refer to  FIG. 3 , there are no restrictions to the type of information transmitted by sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318  in the form of watermarks within a coverage area such as coverage area  302 . For example, in large social gatherings such as a tradeshow, for example, it would be beneficial for the tradeshow participants having common professional interests to be made aware of each other&#39;s identity in order to maximize the probability of having mutually beneficial face-to-face discussions where desired. For example, in this embodiment, assume WTRUs  306   1 ,  306   2 , and  306   n  are registered participants of a trade show. As part of the registration process, participants are requested to provide information regarding themselves such as the industry in which they work and perhaps other relevant information. This information is broadcast as a watermark that can be received and displayed on the WTRUs  306   1 ,  306   2 , and  306   n  of all registered participants.  
         [0056]     Therefore, in this embodiment, assume the user of WTRU  306   1  reviews the information provided voluntarily by other tradeshow participants and notices that the user of WTRU  306   2  is someone with whom the user of WTRU  306   1  would like to meet. In this example, the users of WTRUs  306   1  and  306   2  have a much higher probability of having a mutually productive meeting than if they were arbitrarily looking for people having similar professional interests. Of course, this embodiment may be implemented in any type of large gathering, professional or personal.  
         [0057]     In another embodiment of the present invention, WTRUs  306   1 ,  306   2 , and  306   n  authorized to operate within a coverage area  302  may receive traffic, weather, news, or any other type of information as a watermark broadcast throughout the coverage area  302  by either the base station  304  or the sensors  308 ,  310 ,  312 ,  314 ,  316 ,  318 . The WTRUs  306   1 ,  306   2 , and  306   n  themselves may also transmit such information as watermarks in an ad-hoc fashion.  
         [0058]     In another embodiment of the present invention, more than one type of message can be simultaneously transmitted within data packets in a communication session. This can be accomplished by designating the primary communication signal the cover signal, and designating other types of messages auxiliary data that is embedded in the cover signal. For example, in a wireless telephone conversation, the transmitted and received voice signals can be designated cover signals. Short message service (SMS) messages can be sent simultaneously to or from the WTRU by embedding the messages as watermarks in the voice cover signals. It is noted, of course, that the primary communication signal and auxiliary data are not limited to being a voice signals and SMS messages, but may each be any type of signals. For example, the primary communication signal may be data packets transmitted during a web browsing session. Additionally, it is important to note that this embodiment may be implemented in both the uplink and downlink.  
       Management of Watermarks  
       [0059]     Referring now to  FIG. 4 , there is shown a WTRU  402  and base station  404  configured for managing the use of watermarks. For convenience, only the features of the WTRU  402  are described below as the WTRU  402  and base station  404  are identically configured with respect to management of watermarks. The WTRU  402  includes a watermarking stack  406  wherein at least one watermarking technique  407  is available at, for example, the RF layer (i.e. layer zero)  408 , the physical layer (i.e. layer one)  410 , and layer  2 / 3   412 . The WTRU  402  also includes a watermarking manager  414 . The watermarking manager  414  is configured to evaluate the state of the system including the application being run, intrusion detection status (i.e. have any intruders been recently detected, social group definition (i.e. is WTRU  402  currently being used at a tradeshow type setting as described above), etc. Based on this evaluation, the watermarking manager  414  selects an appropriate watermarking technique/layer or sets of watermarking techniques/layers.  
         [0060]     To coordinate communications between two communicating entities, the watermarking manager  414  may transmit watermarking synchronization information. The watermarking synchronization information may be transmitted separate from a main data flow or as a watermark within the main data flow.  
       Use Of Watermarks For Intrusion Detection  
       [0061]     Referring now to  FIG. 5 , watermarks may be used for intrusion detection. In  FIG. 5 , a base station  504  of a wireless communication system  500  is shown. Operating within a coverage area  502  of the base station  504  are a plurality of WTRUs  506   1 ,  506   2 , and  506   n . Additionally, a plurality of sensors  508 ,  510 ,  512 ,  514 ,  516 ,  518  are deployed at predetermined locations.  
         [0062]     In this embodiment, the WTRUs  506   1 ,  506   2 , and  506   n  are required to insert a particular watermark in their transmissions which are monitored by the sensors  508 ,  510 ,  512 ,  514 ,  516 ,  518 . Where a transmission is detected without the proper watermark, the WTRU from which the non-watermarked transmission was transmitted is flagged as an intruder. It is noted that the watermark may be varied on a periodic basis as an additional security measure.  
         [0063]     In response to detection of an intruder, the base station  504  may take any number of actions. For example, the base station  504  may require that all WTRUs operating within a predetermined distance from the sensor that detected the non-watermarked transmission be re-authenticated. Alternatively, or in combination with re-authentication, the base station  504  may upgrade a security strength indicator for its coverage area  502 . Another option is to broadcast the identity of the intruder to all of the WTRUs  506   1 ,  506   2 , and  506   n  with instructions to ignore the intruder&#39;s requests for the medium. In an 802.11 network, for example, this can be accomplished by ignoring any virtual carrier sense reports from the rogue transmitter. As mentioned above, this is less complicated than ignoring the physical carrier sense, since in that case the determination of the source is made at a higher layer. A watermark broadcasting the currently identified threat can also indicate which network mechanisms should be protected better.  
         [0064]     In the event of a denial of service attack, all network devices can be instructed via watermarks to begin packet-by-packet inspection for a specific TA in the packet headers of network messages and problem packets may be ignored.  
       Watermarking Applications  
       [0065]     Watermarks are preferably used for the authentication, encryption, integrity, and auditing of data. Of course, watermarks may also be used for providing other types of protection in a communication system. To authenticate, a watermark is preferably inserted into a data transmission to authenticate the transmission as being genuine. With respect to encryption, a preferred embodiment of the invention is to include an encrypted version of a key as a watermark inserted into a set of encrypted data. With respect to integrity, conventional hashing functions append an authentication code onto the end of data being transmitted to a receiver. In the present invention, the authentication code is embedded as a watermark. With respect to auditing, in the telecommunications context, auditing can refer to being able to trace the path traversed by a data packet. Such an auditing function can be implemented using watermarking techniques as follows: Suppose that a data packet is sent from A to B via a number of intermediate nodes, referred to as N 1 , N 2 , . . . N M . Each of the intermediate nodes has an associated unique signature (or identifier). As the packet traverses each of these nodes, the node inserts its own identifier as a watermark in the data packet and forwards it to the next node. At the end of the journey, the received data packet has a set of watermarks, which can be analyzed for auditing the communication path. Such an audit process can also be extended to the case where the intermediate nodes are general TRUs. Furthermore, the auditing process may also be used before the data packet reaches the ultimate recipient B.  
         [0066]     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone (without the other features and elements of the preferred embodiments) or in various combinations with or without other features and elements of the present invention.