PTAB

IPR2017-01606

Securus Technologies Inc v. DSI ITI Inc

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: 3-Way Call Detection System
  • Brief Description: The ’704 patent discloses systems and methods for detecting unauthorized three-way calls, particularly in controlled environments like prisons. The technology works by filtering a narrow frequency band from a telephone line, inserting a low-level white noise test signal into that "notched" band, and then monitoring the amplitude of this test signal to detect changes that occur when a third party is added to the call.

3. Grounds for Unpatentability

Ground 1: Obviousness over Johnson and Rao - Claims 1-20 are obvious over the combination of Johnson and Rao under 35 U.S.C. §103.

  • Prior Art Relied Upon: Johnson (Patent 6,141,406) and Rao (Patent 6,141,415).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that the combination of Johnson and Rao discloses all limitations of independent claims 1 (system) and 20 (method).
      • Johnson teaches a system to detect three-way calls by observing changes in the echo characteristics of a telephone connection. Critically, Johnson explicitly suggests the possibility of injecting a low-amplitude reference signal, such as "white noise," to establish a baseline for monitoring, rather than relying solely on the speaker's voice. Johnson’s system includes a processor (DSP) to monitor for changes in the signal path that indicate a three-way call has been initiated. This teaches the core framework of the challenged claims: using an injected signal and a processor to detect three-way calls based on signal path changes.
      • Rao addresses echo problems in speakerphone systems by teaching a specific method to improve signal monitoring. Rao discloses using a notch filter to remove a narrow frequency band from the incoming audio signal, creating a quiet channel. It then uses a detector (e.g., a band-pass filter) to monitor for any energy appearing in that specific notched frequency band, which would indicate near-end speech. This provides the specific filtering and monitoring technique claimed in the ’704 patent.
      • Petitioner contended that combining these references renders the claims obvious. Johnson provides the overall system and purpose (three-way call detection using an injected signal), while Rao provides the specific, well-known technique for creating and monitoring a dedicated frequency band for signal analysis. A person of ordinary skill in the art (POSITA) would apply Rao's more precise filtering method to Johnson's detection system to improve its accuracy. The combination maps directly to the claimed process: filtering a band (Rao), generating and adding white noise to that band (Johnson's suggestion refined by Rao's technique), and processing the signal to detect shifts in a baseline (Johnson). The dependent claims were argued to be obvious as they add only conventional elements, such as specific filter types (notch, band-reject) and processor implementations, all of which are disclosed or suggested in Johnson and Rao.
    • Motivation to Combine: A POSITA seeking to create a more reliable three-way call detection system, as described in Johnson, would have been motivated to incorporate the techniques from Rao. Johnson itself suggests improving its system with other techniques and using non-interfering frequencies for its reference signal. Rao provides a known, analogous method for creating such a non-interfering channel by notching out a frequency band and monitoring it. The motivation was to improve the signal-to-noise ratio and reliability of Johnson's detection concept by using Rao's method to prevent false triggers from normal speech, thereby achieving a more robust system.
    • Expectation of Success: A POSITA would have had a reasonable expectation of success in combining the references. Both relate to signal processing in telephony to analyze echo and signal characteristics. Applying Rao's filtering technique to Johnson's detection system is a straightforward combination of known elements to achieve a predictable improvement in performance. The functionality of notch filters, band-pass filters, and signal processors was well-understood, ensuring the resulting system would work as expected.

4. Key Claim Construction Positions

  • Petitioner argued that the preambles of claims 1 and 20 ("A three way call detection system..." and "A method of detecting...") are not limiting because they merely state an intended use for a structurally and functionally complete invention recited in the body of the claims. Petitioner asserted that even if the preambles were deemed limiting, the combination of Johnson and Rao discloses the recited purpose of detecting the addition of a third party to a call.

5. Relief Requested

  • Petitioner requested institution of an inter partes review and cancellation of claims 1-20 of the ’704 patent as unpatentable.