Detection of duplicate participants in a two-way modem environment

• US 7,006,446 B1
• Filed: 01/14/2000
• Issued: 02/28/2006
• Est. Priority Date: 01/22/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Anderson, Steven E.
• Primary Examiner(s): LEE, CHI HO A
• Application Number:
  US09/889,540
• Time in Patent Office: 2,237 Days
• Field of Search: 370/248, 370/247, 370/251, 370/252, 455/411, 348/180, 348/192
• US Class Current: 370/248
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 2463/101 applying security measures for digital rights management data processing systems or methods, specially adapted for commerce, e.g. marketing, shopping, billing, auctions or e-commerce G06Q30/00
• CPC Class Codes: H04L 63/10 for controlling access to devices or network resources
• CPC Class Codes: H04L 63/1466 Active attacks involving interception, injection, modification, spoofing of data unit addresses, e.g. hijacking, packet injection or TCP sequence number attacks
• CPC Class Codes: H04N 21/2408 Monitoring of the upstream path of the transmission network, e.g. client requests monitoring data switching networks utilization H04L43/0876; scheduling or organising the servicing of application requests H04L67/60
• CPC Class Codes: H04N 21/25808 Management of client data terminal profiles in network data switching protocols H04L67/303
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

Duplicate participants (e.g., cloned subscriber units) (274) are detected in a communication network, such as a hybrid fiber/coax (HFC) cable television network or the like, by monitoring the physical layer of the network to detect transmission differences between such units. The subscriber units (14, 16, 18, 274, 276) may be cable modems that transmit upstream signals with associated identifiers to a headend (10, 200), e.g., to access the Internet or for telephony. Measured characteristics of the upstream signals can include: (1) propagation time (235), (2) frequency (240), (3) power (245), and (4) spectral characteristics (250). For propagation time, the reception time of the upstream message can be compared to a headend clock (215) and also to other messages with the same modem ID. For spectral characteristics, adjustment coefficients can be provided to the units to normalize the spectrum of the upstream signal to a baseline spectrum. When discrepancies are detected for an upstream signal that indicate duplicate modems are operating in the network, the account of the corresponding unit can be terminated.

Claims

1. A method for detecting a clone subscriber unit in a communication network, comprising the steps of:

recording a transmission characteristic of a signal from an original subscriber unit that is authorized for use in said network;

measuring a comparable transmission characteristic of a signal from a subscriber unit on said network alleging to be said original subscriber unit; and

determining whether there is a difference between the measured transmission characteristic and the recorded transmission characteristic;

wherein any such difference is indicative that the alleging subscriber unit is a clone subscriber unit.

2. The method of claim 1, wherein:

said recording, measuring and determining steps occur at a headend of the network.

3. The method of claim 1, wherein:

the measured transmission characteristic is associated with a physical layer of said network.

4. The method of claim 1, wherein:

said network is a hybrid fiber/coax cable television network.

5. The method of claim 4, wherein:

said original and alleging subscriber units are cable modems.

6. The method of claim 4, wherein:

said original and alleging subscriber units comprise hybrid fiber/coax consumer premises equipment.

7. The method of claim 1, wherein:

the recorded transmission characteristic comprises at least one of a propagation time and a propagation time offset for the signal of the original subscriber unit.

8. The method of claim 7, wherein:

the propagation time offset is determined by comparing an assigned propagation time of the signal of the original subscriber unit to a receive time thereof.

9. The method of claim 7, comprising the further steps of:

providing adjustment data to adjust the propagation time offset to a desired value; and

communicating the adjustment data to any subscriber unit in the network that uses an identifier associated with the original subscriber unit for use in adjusting a propagation time offset thereof.

10. The method of claim 9, wherein:

the adjustment data is provided by a headend of the network.

11. The method of claim 9, comprising the further steps of:

determining the propagation time offset by sampling the signal of the original subscriber unit using a clock having a clock rate corresponding to a first resolution; and

providing the adjustment data at a second, coarser resolution.

12. The method of claim 11, wherein:

the clock rate is increased from a nominal level corresponding to said second resolution for recovering upstream transmissions from subscriber units in the network, to a higher level to achieve the first resolution for determining the propagation time offset.

13. The method of claim 11, wherein:

the clock rate operates at the first resolution for initially providing the adjustment data; and

the adjustment data is provided at the second resolution by omitting at least one least significant bit thereof.

14. The method of claim 11, wherein:

the clock rate operates at the first resolution for initially providing the adjustment data; and

the adjustment data is provided at the second resolution by randomizing at least one least significant bit thereof.

15. The method of claim 1, wherein:

the recorded transmission characteristic comprises at least one of a frequency and a frequency offset.

16. The method of claim 15, comprising the further steps of:

providing adjustment data to adjust the frequency offset to a desired value; and

communicating the adjustment data to any subscriber unit in the network that uses an identifier associated with the original subscriber unit for use in adjusting a frequency thereof.

17. The method of claim 1, wherein:

the recorded transmission characteristic comprises at least one of a power and a power offset.

18. The method of claim 17, comprising the further steps of:

providing adjustment data to adjust the power offset to a desired value; and

communicating the adjustment data to any subscriber unit in the network that uses an identifier associated with the original subscriber unit for use in adjusting a power thereof.

19. The method of claim 1, wherein:

the recorded transmission characteristic comprises a spectral characteristic.

20. The method of claim 19, wherein:

the spectral characteristic comprises at least one of a power spectrum and a power spectrum offset.

21. The method of claim 20, comprising the further steps of:

providing adjustment data to adjust the power spectrum offset to a desired value; and

communicating the adjustment data to any subscriber unit in the network that uses an identifier associated with the original subscriber unit for use in adjusting a power spectrum thereof.

22. The method of claim 21, wherein:

the adjustment data comprises filter coefficient data.

23. The method of claim 1, wherein:

the recorded transmission characteristic is obtained from a measurement of the signal of the original subscriber unit.

24. An apparatus for detecting a clone subscriber unit in a communication network, comprising:

means for recording a transmission characteristic of a signal from an original subscriber unit that is authorized for use in said network;

means for measuring a comparable transmission characteristic of a signal from a subscriber unit on said network alleging to be said original subscriber unit; and

means determining whether there is a difference between the measured transmission characteristic and the recorded transmission characteristic;

wherein any such difference is indicative that the alleging subscriber unit is a clone subscriber unit.

25. An apparatus for detecting a clone subscriber unit in a communication network, comprising:

means for recording a transmission characteristic of an original subscriber unit authorized for use in said network; and

means for comparing said recorded transmission characteristic to a comparable transmission characteristic of a subscriber unit on said network alleging to be said original subscriber unit;

wherein a difference between the compared transmission characteristics is indicative that the alleging subscriber unit is a clone subscriber unit.