Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M3/00—Automatic or semi-automatic exchanges
  • H04M3/08—Indicating faults in circuits or apparatus
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M3/00—Automatic or semi-automatic exchanges
  • H04M3/22—Arrangements for supervision, monitoring or testing
  • H04M3/26—Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
  • H04M3/28—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
  • H04M3/30—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop
  • H04M3/302—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop using modulation techniques for copper pairs
  • H04M3/303—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop using modulation techniques for copper pairs and using PCM multiplexers, e.g. pair gain systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
  • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
  • H04M11/062—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors using different frequency bands for speech and other data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M2201/00—Electronic components, circuits, software, systems or apparatus used in telephone systems
  • H04M2201/18—Comparators

Definitions

• Method and communication arrangement for detecting at least one further communication device that can be connected to at least one subscriber line
• the subscribers or the communication terminals assigned to the subscribers - such as, for example, network termination devices (NT network termination) - are connected to central switching devices or digital multiplexer devices (also referred to as DSLAM, digital subscriber line access multiplexers) via subscriber connection lines.
• the subscriber-side communication terminals or the switching devices are connected to the respective subscriber line - which can be designed, for example, as a two-wire or four-wire line - via a subscriber line unit or a modem arranged in the respective subscriber line unit, the data Communication between the modems can take place via the subscriber line, for example by means of an xDSL transmission method.
• This situation is also referred to as tapping the subscriber line (wire tap).
• the typical tapping of the subscriber line is shown schematically as an example.
• the subscriber connects a communication device B to a switching device A via a subscriber line TAL.
• a further communication device C as a listening device via a stub SL with the Subscriber line TAL connected.
• the connection of the interception device C to the subscriber line TAL is implemented in such a way that the interception device C can receive all information transmitted bidirectionally via the subscriber line TAL.
• the invention is therefore based on the object of improving the detection of monitoring devices connected to a subscriber line and thus ensuring or guaranteeing secure data transmission via the subscriber line.
• the connection of monitoring devices with a high input impedance to the subscriber line should also be detected.
• the object is achieved by a method and by a communication arrangement according to the features of claims 1 and 8.
• the essential aspect of the method according to the invention for the detection of at least one further with at least one part Communication device that can be connected to the subscriber line consists in that the transmission function of the at least one subscriber line is monitored for significant changes, the detection of the at least one further communication device connected to the subscriber line being displayed when a significant change in the transmission function is ascertained.
• the main advantage of the method according to the invention is that even the connection of monitoring devices with a high input impedance to a subscriber line is recognized or detected. Furthermore, with the aid of the method according to the invention, it can be checked whether, in addition to a planned number of communication devices connected to a subscriber line, further communication devices are connected to the subscriber line or to the subscriber line. Illegal intrusion of communication devices - e.g. illegal use of a subscriber line by third parties - are recognized.
• the transfer function of the subscriber line is recorded at approximately periodic time intervals and an average value of the transfer function is derived from the detection results.
• the deviation of the currently determined transfer function from the mean value of the transfer function is monitored, the detection of the at least one further communication device being displayed when a deviation is found above a predetermined threshold value.
• FIG. 1 shows a connection scenario with a listening device connected to a subscriber line.
• FIG. 2 shows the division of a transmission channel formed by the subscriber line with regard to the Shannon capacity from the point of view of the listening device.
• FIG. 3 shows the sequence of the method according to the invention in the form of a self-explanatory flow chart
• the communications device represents a central switch or a multi- tiplexer worn to which a subscriber line TAL a subscriber - not shown - by means of ei ⁇ ner configured as a network termination device communication device B is connected.
• the communication devices A, B are connected to the subscriber line TAL via an xDSL modem MOD.
• the principle of the method according to the invention is that in the case of a “clean” subscriber line, that is to say in the case of a subscriber line without a monitoring device C connected to it, as much as possible of line-specific information such as, for example, the transmission function, background noise, etc.
• subscriber line device - is recorded and recorded or stored or untapped subscriber line device - with at least two communication devices connected to one another via this subscriber line - generally has strictly linear time-invariant properties and can therefore be characterized or identified in the frequency domain by its transfer function H current .
• H current When connecting to another communication device, for example, the locus of the input impedance of the subscriber line changes resulting in a significant change in the transfer function H _ cur ront result has.
• the transfer function H cu rent of the subscriber line is checked for significant changes, a significant change in the transfer function H cürent being indicated by an alarm message.
• All current xDSL transmission methods (CAP, DMT, QAM, TH-PHM) start with a so-called training phase, in which the transmission function H current of the subscriber line is determined implicitly (equalizer coefficients for QAM) or explicitly (for DMT).
• Such routines are already implemented in terms of hardware, ie in the form of a chipset in the individual connection units or modems.
• the method according to the invention can be carried out on both sides of the subscriber line TAL, for example by means of the xDSL modem arranged in the switching center A and / or by the xDSL modem arranged in the network termination device B.
• the transfer function H curren t can be recorded both during the current information transfer via the subscriber line TAL and, for example, as part of the standardized training process according to ITU-T G.992.3 - double-ended loop test (DELT),
• the currently recorded transfer function H currer , t is usually stored in the form of frequency-dependent coefficients, the stored information being called up cyclically and further processed as part of the method according to the invention.
• R represents the achievable bit transfer rate
• the information security is greater the closer the data communication between the communication units involved moves to the Shannon capacity. Additional security in the detection of eavesdropping devices is achieved if the bandwidth of the data communication carried over the subscriber line is expanded with the aid of specific bandpass signals (such as pilot tones or bandpass pseudo noise).
• bandpass signals such as pilot tones or bandpass pseudo noise.
• a listener will normally not pay attention to the frequency range outside the standardized communication bandwidth (e.g. 2.2 MHz with ADSL transmission methods), so there is a high probability that a listening attempt by characteristic echoes in this extended bandwidth range will be detected. This improvement is easy to implement because current commercially available modems are able to detect the transmission function even in this extended bandwidth range.
• the cost function Q for displaying eavesdropping devices connected to the local loop is defined as follows
• the norm of the recorded transfer function H is in accordance with the L 2 norm
• N represents the number of subcarriers of the xDSL signal.
• Detection of a listening direction i.e. the submission of an alarm message is based on a threshold value t, the condition according to the self-explanatory flowchart shown in FIG.
• the subscriber connection lines can be configured as two-wire or four-wire or N-wire lines.
• the L2 standard of the transfer function H is determined as follows depending on the number of wire pairs per subscriber line TAL
• M number of line pairs per subscriber line (xDSL connection)
• N number of subcarriers representing the xDSL signal.
• xDSL modems can advantageously be used to implement the method according to the invention, since they already have mechanisms for detecting the transfer function of subscriber lines as part of the standard-compliant training phase or prequalification method, so that this information only has to be processed further within the scope of the method according to the invention.

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Telephonic Communication Services (AREA)
• Monitoring And Testing Of Exchanges (AREA)

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Publications (1)

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• 2003
  • 2003-09-16 DE DE10342806A patent/DE10342806A1/de not_active Withdrawn
• 2004
  • 2004-08-05 CN CNB2004800266885A patent/CN100531255C/zh not_active Expired - Fee Related
  • 2004-08-05 EP EP04766432A patent/EP1665754A1/de not_active Withdrawn
  • 2004-08-05 US US10/571,745 patent/US20070071229A1/en not_active Abandoned
  • 2004-08-05 WO PCT/EP2004/051727 patent/WO2005032113A1/de active Application Filing

Patent Citations (1)

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