Case 6:24-cv-00298-DC-DTG Document 1-4 Filed 05/30/24 Page 1 of 59
`Case 6:24-cv-00298-DC-DTG Document1-4 Filed 05/30/24 Page 1 of 59
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`EXHIBIT 4
`EXHIBIT 4
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`Case 6:24-cv-00298-DC-DTG Document 1-4 Filed 05/30/24 Page 2 of 59
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`IN THE UNITED STATES DISTRICT COURT
`FOR THE WESTERN DISTRICT OF TEXAS
`WACO DIVISION
`
`VOIP-PAL.COM, INC.
`Plaintiff,
`
`v.
`T-MOBILE USA, INC.;
`Defendant.
`
`CIVIL ACTION NO. : 6:24-cv-298
`
`JURY TRIAL DEMANDED
`
`DECLARATION OF DANIJELA CABRIC, PH.D.
`
`I, Dr. Danijela Cabric, declare as follows:
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`I.
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`INTRODUCTION
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`1.
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`I have personal knowledge of the facts contained in this declaration and I could
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`competently testify to those facts as a witness. In preparing this Declaration, I have reviewed the
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`following, as well as the other documents discussed herein:
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`a. U.S. Patent No. 8,542,815 (“the ’815 Patent”) and its file history;
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`b. U.S. Patent No. 9,179,005 (“the ’005 Patent”) and its file history;
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`c. U.S. Patent No. 10,218,606 (“the ’606 Patent”) and its file history.
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`2.
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`I have been retained by VoIP-Pal.com, Inc. (“VoIP-Pal”) as an expert in the fields
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`of computer science, computer communications, and related technologies. I am being
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`compensated at my consulting rate of $500 per hour. My compensation is not dependent on and
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`in no way affects the substance of my Declaration. I have no financial interest in VoIP-Pal or in
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`VoIP-Pal’s patents.
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`II.
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`QUALIFICATIONS
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`3.
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`My technical qualifications are as follows. I hold a Ph.D. in Electrical Engineering
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`in 2007 from the University of California, Berkeley in Berkeley, CA, for research on the topic of
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`“Cognitive Radios: System Design Perspective,” under the supervision of Dr. Robert W.
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`Brodersen. Previous to that, I received a M.S. in Electrical Engineering in 2001 from the
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`University of California, Los Angeles (“UCLA”), based on a thesis entitled, “Characterization of
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`a Fast Frequency-Hopped FSK Testbed through Simulations and Field Trials.”
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`4.
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`I am a Full Professor of Electrical Engineering at University of California, Los
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`Angeles. I have been a full, tenured professor in the Department of Electrical Engineering at UCLA
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`since 2018. My research interests include digital communications and wireless system design. I
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`am aware of the knowledge that a person of ordinary skill in the art would have had at the time the
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`invention was made.
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`5.
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`I have taught undergraduate and graduate courses at UCLA and at UC Berkeley.
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`For example, I have taught the following undergraduate courses at UCLA: Signals and System,
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`Digital Signal Processing, Logic Design for Digital Systems, Circuit Analysis I, Digital Electronic
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`Circuits. I have also taught graduate courses at UCLA including Estimation and Detection, Digital
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`Communications, Wireless Communication System Design, Modeling and Implementation.
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`Further, I developed a new graduate-level course titled: Special Topics in Circuits and Embedded
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`Systems: Wireless Communications System Design. At UC Berkeley, I taught the undergraduate
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`course Probability and Random Processes and was a graduate-level course consultant for the
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`course VLSI Signal Processing.
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`6.
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`I am a Fellow of the Institute of Electrical and Electronics Engineers (IEEE) and
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`have also been recognized by the IEEE as a ComSoc Distinguished Lecturer from 2018-2020. In
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`2020, I received the Best paper Award at the 4th ACM Workshop on Millimeter-Wave Networks
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`and Sensing Systems, and the year before, in 2019, I received the Best paper Award at the IEEE
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`International Conference on Communications, Networking, and Computing. I am the author or
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`co-author of at least five books or chapters, 70 journal publications, eight magazine articles, 126
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`conference papers, 17 invited papers, 1 patent and 2 patent applications. I have also been invited
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`to speak at about 62 talks, panels, keynotes, or tutorials. I am the author or co-author of over 250
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`technical publications in the areas of communications, communications signal processing,
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`networking, embedded systems and integrated circuits.
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`7.
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`I have also been hired by several technology companies as a consultant, including
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`Amazon, Inc., Perceptronics Solutions, LocatorX, Intellectual Ventures, and Specom, Inc. I have
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`also served on the Board of Advisors for MaxLinear, Inc.
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`8.
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`My Curriculum Vitae provides a more detailed description of my qualifications,
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`experience, publications, awards and patents, as well as a list of cases in which I have testified at
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`trial, hearing, or by deposition within the last four years.
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`III. TASK
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`9.
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`I have been asked to review the VoIP-Pal patents listed above and provide context
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`regarding the understanding of these patents of a person of ordinary skill in the art (“POSITA”) at
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`the time of invention. I have also been asked to provide some background information and
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`comparisons to other communication systems, including an assessment of what inventive concepts
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`claimed in the VoIP-Pal patents would not have been well-known, routine or conventional to the
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`POSITA.
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`10.
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`Based on my review of the above-mentioned patents and my background and
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`experience in the field of computer science, it is my opinion that one of ordinary skill in the art as
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`of the priority date would be someone with an undergraduate degree in either Computer Science,
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`Computer Engineering, Electrical Engineering, or a closely related discipline. Furthermore, I
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`believe that such a person would also have 2 years of experience in system-level software
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`development. In my opinion a greater degree of professional experience could serve to replace
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`some degree of formal education. I also believe that some greater degree of formal education
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`could serve to replace some degree of professional work experience.
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`A.
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`11.
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`Background of the Technology of the Patents
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`The earliest telephone systems to receive public use within the United States
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`involved a telephone directly connected to a switchboard that had a human operator. The operator
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`was signaled when the portion was lifted from the hook. A caller would then identify the person
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`they wished to call to the operator. If the callee was connected to the same telephone switch board,
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`the operator would physically pull out a cable associated with the caller’s phone and plug the cable
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`into a socket associated with the callee’s telephone. If the callee was associated with a different
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`switchboard, the operator would connect the caller to an appropriate switchboard with a different
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`human operator. This arrangement was error prone (e.g., operators would often connect the wrong
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`party) and limited the number of possible telephones because of the physical limits of switchboards
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`and cables to be pulled. This basic system developed into the traditional analog telephone service,
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`also called the Plain Old Telephone Service (“POTS”), in which there was a dedicated, point-to-
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`point electrical connection between the caller and callee.
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`12.
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`Rotary dialing eventually was introduced, beginning at around the turn of the 20th
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`century, where a rotary disk was marked with numbers from zero to nine. A caller would spin the
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`wheel and a mechanical device in the telephone would cause a sequence of electrical pulses to be
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`sent to the network corresponding to the digit dialed, for example, four pulses would be sent for
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`the number four. Rather than speaking to a human operator, an electric device would count the
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`pulses and begin to route a call once an appropriate and valid sequence of digits was dialed by the
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`caller. This advancement improved reliability of call routing and reduced the time required to
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`initiate a call but there was still a dedicated, point-to-point electrical connection between the caller
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`and the callee. As multiple companies began to provide telephone services and the number of
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`customers increased, a caller could be a customer of one telephone company and the callee could
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`be a customer of another. To address this problem, trunk lines were used to connect one company
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`to another.
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`13.
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`Eventually, as the number of companies continued to increase and telephone
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`services spread over much larger geographic areas, the notion of a Public Switched Telephone
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`Network (“PSTN”) emerged. Dedicated wires were used to connect a caller and callee and were
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`“circuit-switched” to connect these two participants. The PSTN developed gradually into the
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`middle of the 20th century, still built around rotary dialing and circuit-switched, analog POTS
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`connections to individual telephones. A circuit-switched network assigns dedicated resources,
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`such as switch settings and specific wires, to connect a caller to a callee. While the call is ongoing,
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`these resources cannot be used for any other communications.
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`14.
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`The next important advancement for consumer telephone service, introduced
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`broadly during the second half of the 20th century, was the introduction of push-button telephones.
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`The rotary dial was replaced by a matrix of buttons, each labeled with a digit from zero through
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`nine along with the additions of ‘*’ and ‘#’. The underlying signaling technology was dual-tone
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`multiple-frequency (“DTMF”) and involved two different audible tones being sent simultaneously
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`from the telephone into the telephone network. A receiver within the network decoded these tones
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`and formed them into a sequence of digits indicating the number of the callee.
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`15.
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`Around this time a scheme for international telephone addressing was introduced,
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`with a numeric protocol for identifying one country from another and providing country-specific
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`routing within the destination country. The E.164 standard now documents how telephone
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`numbers can be uniquely identified. Local rules govern how to dial a telephone number to cause
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`a telephone call to be routed. While many advances, such as DTMF dialing and automated
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`international routing, may have been originally introduced via ad hoc methods, eventually they
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`required multiple parties (companies and governments) to agree on standards to enable wide-
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`spread reliable use and inter-operability among different physical communications networks.
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`Even with these advances, the systems still relied on circuit-switched technology that dedicated
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`resources between callers and callees during the call.
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`16.
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`The move to take human operators out of the loop, with the introduction of rotary
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`dialing, combined with the fast increase in demand for telephone services throughout the 20th
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`century, resulted in the development of automated telephone switches. These switches originally
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`supported analog voice calls initiated via rotary dialing and dedicated ports as well as physical
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`wires for each circuit-switched call. Eventually analog voice services were replaced within the
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`network with digital voice. Digital voice is communicated using a sequence of chunks (or packets)
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`of data. This advancement allowed the physical resources to be shared among multiple calls over
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`short bursts of time. For example, a physical wire can move a packet for one call at a specific
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`instance in time and then move a packet for a totally different call subsequently, only to later return
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`to transfer a new packet for the original call. This advance is called packet-switched
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`communications and provided an important increase in network reliability and efficiency while
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`driving down the cost. However, in most situations throughout the 20th century (and often still
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`today), the connection to the end user’s physical telephone is analog. The conversion between
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`analog and digital encoding is commonly done at the point where the PSTN network switch
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`connects to the POTS handset, for example, at a Class-5 telephone switch, which connects the
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`POTS handset to the PSTN at the service provider’s central office. Various signaling protocols
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`were used to setup calls through switches at PSTN central offices or exchanges including in-band
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`signaling, which was superseded by out-of-band signaling (e.g., “Signaling System 7” or “SS7”).
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`17.
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`The Internet became important to consumers, via broad deployment, during the late
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`1980’s and early 1990’s. Eventually available bandwidth and reliability increased to the point
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`where pioneers began to experiment with techniques to carry voice communications over the
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`Internet. These early efforts then began to focus on techniques called Voice Over Internet Protocol
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`(VoIP) and session initiation protocol (SIP). VoIP provided a consistent set of protocols and
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`mechanisms for moving digital voice packets between two callers using the Internet rather than
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`existing PSTN networks. For example, SIP provided a mechanism for establishing and terminating
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`these calls between users of a VoIP service. Furthermore, a callee could register with a VoIP
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`service so that an identifier (such as their name, email address or a nickname) could be associated
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`with the computer to which they were logged in. Eventually VoIP services expanded to provide
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`interoperability with the existing PSTN services. For example, the company Skype began to allow
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`a user to call a PSTN number using a feature marketed as “Skype out”. However, the user was
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`required to explicitly classify the call as a PSTN call by specifying a real physical telephone
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`number. In this case the VoIP system included a gateway between the VoIP network and the PSTN
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`network in order to route to the PSTN telephone. Calls placed to a proprietary non-PSTN user
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`identifier, such as an email or nickname, however, remained within the VoIP network and were
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`not routed to the PSTN network and did not connect to a POTS telephone.
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`18.
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`The advent of VoIP technology allowed customers to physically move their
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`telephones from one location to another, even from one continent to another, with no fundamental
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`change in its operation from the point of view of a caller once a connection to the Internet was
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`established. However, the integration of network equipment to route between different types of
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`networks using VoIP, for example from a VoIP caller in Europe to a PSTN callee in the United
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`States, introduced a number of new complications. The VoIP service needed to be able to
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`distinguish between callees within the VoIP network and those outside of it and thus required
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`different methods for identifying callees and routing to them depending on whether the callees
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`were within or outside the VoIP network. One way to identify callees on the VoIP network was
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`to use a predefined proprietary user identifier such as an email or nickname. The VoIP service
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`provider also needed to interpret dialed PSTN numbers in order to correctly route calls to a PSTN
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`callee. A VoIP caller had to use different types of callee identifier depending on whether or not
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`the destination (callee) was within the VoIP network or not. The caller’s choice of the type of
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`callee identifier thus explicitly specified the destination network.
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`19.
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`Starting from about the 1960’s, some organizations desired to take greater control
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`over their telephony network and thus created a privately controlled network by using a private
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`branch exchange (PBX), which was a kind of private switch that allowed them to assign their own
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`internal phone numbers or “extensions” to their users (for example, short three- or four-digit
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`numbers for convenient dialing) and also to control calls over their internal network without
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`recourse to the public switch telephone network (PSTN). Keeping internal calls on their internal
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`network also allowed these organization to avoid some of the expense of using an external network
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`such as the PSTN. As networks migrated to Voice-over-IP (VoIP), some of these PBXs began to
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`support VoIP protocols over a packet switched network. However, the typical method of operation
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`required the user to dial a special code to signal to the PBX when a PSTN number was being
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`dialed, which would be sent to the PSTN. For example, it was typical to require the user to “dial
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`9” to send a call over an outside line to the PSTN, whereas other dialed numbers were interpreted
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`as internal and were routed internally provided that they identified a valid extension. Again, the
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`user manually specified the selection of the network on which the call should be routed by their
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`manner of dialing (e.g., by dialing ‘9’). Inwardly bound calls from the PSTN were typically passed
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`through a receptionist connected to the PBX. Some PBX systems had Direct Inward Dialing (DID)
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`features to allow incoming calls to be routed directly to a specific extension or phone within the
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`organization’s Private Branch Exchange (PBX) system, bypassing the receptionist. Organizations
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`purchased telephone numbers from a PSTN telephone company and assigned them to individual
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`PBX extensions within the company. The first DID service for PBXs in the U.S. appears to have
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`been developed by AT&T starting in the 1960s, nowadays typically delivered on a Primary Rate
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`Interface (PRI) circuit. The use of DID lines on PBX systems benefited organizations for several
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`reasons: it allowed callers to reach specific extensions directly, without the need for a receptionist
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`or interactive voice response system; it allowed existing and new PSTN phone numbers to be
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`assigned to particular local extensions by the PBX administrator; it allowed a large number of local
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`extensions to share a smaller number of physical PSTN lines, with only some extensions having
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`dedicated PSTN phone numbers. Typically, an organization that operated its own PBX would buy
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`a block of PSTN numbers from a PSTN service provider (e.g., AT&T) such that if any of those
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`numbers were dialed, they were forwarded by AT&T to the PBX, which in turn, would distribute
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`the call to the appropriate extension based on the PBX configuration. This enabled the direct
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`inward dialing of calls from the PSTN to PBX users. Conventionally, however, outgoing calls
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`from PBX users to PSTN numbers were signaled by the PBX users dialing a certain prefix (e.g.,
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`“9”), thus PBX users specified routing over the PSTN by dialing this prefix. By way of
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`background, direct inward dial numbers and lines (DIDs) were sometimes referred to as “Direct-
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`in-Dial numbers”, “DID lines”, “Direct Dial-in numbers”, “DDI numbers,” “DDI lines”, or private
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`direct dialing numbers, for example.
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`20.
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`Digifonica’s advancements over the prior art. The above-described history and
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`technical background serves to provide important context for understanding and recognizing the
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`benefits of the technology disclosed and claimed in the asserted VoIP-Pal patents, which were
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`formerly assigned to a predecessor-in-title company, namely, Digifonica. At a high level, VoIP-
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`Pal’s ’815 and ’005 Patents describe and claim improved methods of routing and interoperability
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`as between a private network and the PSTN and included inventive concepts that were not well-
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`understood, routine or conventional in the prior art, as will be further described and explained
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`below. VoIP-Pal’s ’606 Patent is focused mostly on improved methods for routing within an
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`interconnected communication network comprising multiple nodes or network elements. I will
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`begin by discussing the ’815 and ’005 Patents, and then will discuss the ’606 Patent.
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`B.
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`21.
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`Discussion of the ’815 and ’005 Patents
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`Claim 14 of the ’815 Patent. By way of example, Claim 14 of the ’815 Patent
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`provides improvements and inventive concepts that go beyond Claim 1. Claim 14 recites, “The
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`process of claim 7 further comprising, causing a database of records to be searched to locate a
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`Direct-Inward-Dial (DID) bank table record associating a public telephone number with said
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`reformatted callee identifier and if said DID bank table record is found, classifying the call as a
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`private network call and if a DID bank table record is not found classifying the call as a public
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`network call.” Claim 7 of the ’815 Patent recites, in turn, “The process of claim 1 further
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`comprising formatting said callee identifier into a pre-defined digit format to produce a re-
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`formatted callee identifier.” In view of the patent specification and the claims, a POSITA would
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`understand Claim 7 as disclosing that a callee identifier can be transformed to a callee identifier in
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`a format recognizable by the system for DID searching (Claim 14) and subsequent use in routing
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`(Claim 1). While some preferred embodiments of a reformatting technique are discussed in the
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`’815 Patent with reference to Figure 8B, a POSITA would appreciate that other methods could be
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`used to generate an identifier that the system can use to identify a route to the callee. This is
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`discussed in further detail below.
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`22. More particularly, Claim 14 of the ’815 Patent recites causing a database of records
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`to be searched to locate a DID bank table record associating a public telephone number with the
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`callee identifier. A public telephone number or DID number would be one that is recognizable as
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`a PSTN compatible number, for example, a number compatible with the E.164 standard for PSTN
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`telephone numbers. As a POSITA would understand, such a number would, for example, typically
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`include a country code (CC), a national destination code (NDC) or area code, and a subscriber
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`number (SN). See id., 19:4-18, 22:34-44. A DID number or “public number”, as recited in the
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`claim, could include PSTN-based geographical indications helpful for routing to PSTN locations.
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`For example, a PSTN number could include “44” as a country code (to represent the United
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`Kingdom) or “1” (to represent the U.S./Canada) , for example, and an area code such as “604” or
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`“778” to represent areas associated with Vancouver, Canada. See ’815 Patent at 18:32-37, Figures
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`9, 10 and 12. When expressed in a human-readable form, an E.164 formatted number typically
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`looks like this: +[Country Code][National Destination Code][Subscriber Number]. For example,
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`a number in London might be formatted as +44 20 1234 5678, where “44” is the country code for
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`the UK, “20” is the NDC for London, and “1234 5678” is the subscriber number. A POSITA
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`would understand that the E.164 format is exemplary and that not all parts of the string may be
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`necessary to represent a PSTN number if the format is understood. For example, a “+” is not
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`necessary if it is understood that the first digit or digits of a number represent a country code (e.g.,
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`the leading “1” in item 283 in Fig. 14 is a code representing Canada/US). See id., Figs. 13-14 and
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`19:15-18. In some contexts, a PSTN number may be represented in shorter form, for example, by
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`omitting features such as the country code when a “local” PSTN number is being called. See id.,
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`21:65-22:6. As another example, the same local PSTN number might alternatively be dialed in a
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`national style by prepending a national dialing digit. See id., 21:33-37. Similarly, a POSITA
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`would recognize that public numbers could be represented by a variety of different DID database
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`formats, so long as they were consistent and recognizable; for example, a country code could be
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`omitted or implicit from a DID record in some internal system representations of a PSTN number
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`(e.g., the system might be configured to assume that a 10-digit phone number is located in
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`Canada/U.S., which nevertheless would be associated with a specific user on the PSTN network).
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`Id., 19:4-10, 22:44-48. In other words, a POSITA would understand that there are many ways to
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`represent a public number. The E.164 format is not the only format for specifying public numbers,
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`nor does it mandate how to validly dial a telephone number, which can vary in different locations.
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`A POSITA would recognize from Claim 14 that the claimed system associates public numbers
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`with “direct-inward-dial” (DID) records, which indicates the ability to receive calls from the PSTN
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`(which is how a “DID” has been conventionally defined). However, a POSITA would recognize
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`that Claim 14 indicates that a DID information database is searched for subscriber-initiated
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`outgoing calls, not just direct inward calls from PSTN telephones incoming from non-subscribers
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`(e.g., via a gateway).
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`23.
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`Claim 14 includes an unconventional inventive concept: using a DID database to
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`configurably remap public callee identifiers from both private and public network sources to route
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`calls to a private network node or PSTN gateway. As discussed above, a DID number was
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`typically used in PBXs to route inward-bound calls from the PSTN to a specific “extension” of the
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`PBX (whereas calls between PBX users were made by dialing shorter PBX extension numbers).
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`Similarly, the patent specification would indicate to a POSITA that stored DID information is
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`“associated with the user on the PSTN network”, meaning that PSTN callers could call into the
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`system based on the DID information that would be associated with a system subscriber upon
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`registration, for example. See id., 19:4-10. Notably, Claim 14 recites a database mechanism for
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`associating public (PSTN) numbers with user devices and integrating the routing of
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`communications to a specific subscriber (associated with a DID entry) both from other subscribers
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`(i.e., subscribers of the private network who are calling the specific subscriber from the private
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`network) and from non-subscribers who are calling the specific subscriber from the PSTN (e.g.,
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`via a gateway). Locating DID information for the called subscriber in the DID database is how
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`the call is classified as a private network call (compare “classifying” in Claims 1 and 14), which
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`is used for “producing a private network routing message for receipt by a call controller” to effect
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`the routing of the communication to “an address, on the private network, associated with the
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`callee” (Claim 1). In summary, DID-based calls from both private network subscribers and non-
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`subscribers are routed to the called subscriber over the private network.
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`24.
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`A POSITA would recognize that DIDs were conventionally used for direct inward
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`dialing in PBXs. Similarly, in the context of the patent, the POSITA would recognize that a DID
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`would setup calls from the PSTN such as through a third party invite. Id., 16:56-62, 17:11-15.
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`However, the scenario in Claim 14 points to some unconventional differences. In Claim 14, the
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`application of DID information effectively merges the aforesaid routing of communications from
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`public network sources (i.e., direct inward dialed calls from the PSTN) with those from private
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`network sources (i.e., DID-based calls from other subscribers of the private network) to route to
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`the called subscriber. However, for calling subscribers, the same DID database information is
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`Case 6:24-cv-00298-DC-DTG Document 1-4 Filed 05/30/24 Page 15 of 59
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`used to classify the call as to which network to use for subsequent routing (private or public).
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`Compare Claims 1 and 14. In cases where a search of the DID database located DID information
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`associated with the callee identifier received from the caller’s device, the availability of that
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`information is how the call is classified as a “private network call” to produce a “private network
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`routing message.” The absence of related DID information in the DID database is how it is
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`determined that the call should not be placed on the private network, i.e., it is how the call is
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`classified as a “public network call” to produce a “public network routing message,” to effect the
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`appropriate routing with a call controller. Id. In both cases, the calling subscriber does not specify
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`which network (public or private) to use for routing the call, and indeed, does not need to know
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`this because of the use of DID information. In contrast, conventional PBXs used DIDs for
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`incoming PSTN calls but outgoing calls from behind the PBX were made without using a DID by
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`the caller explicitly selecting which network to use (the PBX’s private network or the PSTN) by
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`the manner of placing the call. If the caller dialed a special code such as “9”, subsequent digits
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`were interpreted as (and sent to) the PSTN via the PBX. However, calls within the PBX internal
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`network were placed by dialing extension numbers which were different than the PSTN numbers
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`represented by the DIDs. The DID number of the called subscriber was not used for classifying
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`or routing the dialed call. Indeed, the DID number would not normally even be dialed by the caller
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`unless the caller was calling from outside the PBX (e.g., from a mobile phone or home phone),
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`that is, from a distinct external communication system.
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`25.
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`Furthermore, in PBX systems, it was not practical to dial the PSTN number
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`represented by the DID number directly on the PBX since the leading digits of the DID number
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`could overlap with and interfere with the dialing of private numbers (i.e., extensions) defined by
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`the PBX operator. For example, consider a scenario in which a first subscriber wanted to call a
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`14
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`Case 6:24-cv-00298-DC-DTG Document 1-4 Filed 05/30/24 Page 16 of 59
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`second subscriber having a DID with a “604” area code (see Fig. 14, item 274 of the ’815 Patent:
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`“1 604 867 5309”). If the first subscriber was calling from within Vancouver, they might interpret
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`the number as a local number (“604” is a typical Vancouver area code), and if so, they might want
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`to dial “604-867-5309” (if 10-digit dialing was the local PSTN dialing convention), but this would
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`potentially conflict with the dialing of PBX extension numbers starting with these digits (e.g.,
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`“6048”). However, if the local convention was 7-digit dialing, the caller might wish to dial “867-
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`5309”, which would conflict with dialing PBX extensions starting with those digits (such as
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`“8675”).
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`26.
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`Another problem is that a conventional PBX was unable to interpret and follow
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`changing local dialing conventions without interference with its existing private extension
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`numbers. Whenever PSTN dialing conventions changed, if the PBX user tried to directly dial
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`PSTN numbers according to the new convention, it would create a new set of conflicts. For
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`example, Vancouver switched from 7-digit dialing to 10-digit dialing in 2001, and the rest of
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`British Columbia switched in 2008. See: < https://www.cbc.ca/news/canada/vancouver-gets-10-
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`digit-dialing-1.275934>
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`and <https://www.canada.ca/en/news/archive/2007/06/new-dialing-
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`come-british-columbia.html>. As a further problem, PBX users from outside the local area
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`associated with “604” could try to dial “1-604-867-5309” (which includes a “1” national dialing
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`digit for long-distance calls), but that could interfere with still other kinds of local extensions. To
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`avoid such problems, PBXs required the use of a special code (e.g., dial “9”) to signal the caller’s
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`intention to dial a PSTN number, which was then routed to the PSTN. Nor was dialing DIDs
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`desirable since PBX users dialed short extension numbers to reach other PBX users. In summary,
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`trying to dial DID numbers on a PBX system would not work reliably or was impractical. A
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`POSITA would recognize that DID numbers in traditional PBXs were for the use of callers outside
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`15
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`Case 6:24-cv-00298-DC-DTG Document 1-4 Filed 05/30/24 Page 17 of 59
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`the PBX, whereas in the ’815 and ’005 Patents, a system is disclosed in which DID-bas