United States Patent
`
`[19]
`
`Russell et al.
`
`[11]
`
`[45]
`
`Patent Number:
`
`Date of Patent:
`
`6,091,722
`
`Jul. 18, 2000
`
`US006091722A
`
`[54] SUBSCRIBER LOOP BYPASS MODEM
`
`[75]
`
`Inventors: Steven P. Russell, Menlo Park; James
`E. Dunn, Escondido; Donald M.
`Bellenger, Los Altos Hills, all of Calif.
`
`[73] Assignee: 3Com Corporation, Santa Clara, Calif.
`
`[21]
`
`[22]
`
`[51]
`[52]
`[58]
`
`[56]
`
`Appl. No.: 08/819,873
`
`Filed:
`
`Mar. 18, 1997
`
`.................................... .. H04L 12/64
`Int. Cl.7
`........................... .. 370/352; 375/222
`U.S. Cl.
`Field of Search ................................... .. 370/493, 494,
`370/495, 352, 353, 354, 355, 356, 401,
`420, 395, 375/222, 379/93.07
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,237,561
`5,428,608
`5,610,910
`5,668,857
`5,719,901
`5,751,700
`5,784,683
`5,889,774
`
`............................. .. 370/29
`Pyhalammi
`Freeman et al.
`.
`Focsaneanu et al.
`McHale et al.
`Le Riche et a].
`Land et al.
`.......... ..
`Sistanizadeh et al.
`Mirashrafi et al.
`
`8/1993
`6/1995
`3/1997
`9/1997
`2/1998
`5/1998
`7/1 998
`3/1999
`OT1 IER PUBLICATIONS
`
`..... .. 370/351
`379/93.07
`.. 375/222
`370/352
`455/5.1
`370/352
`
`Patrick, Dennis R., “The Telecommunications Act of 1996:
`Intent, Impact and Implications”, from website http://ww-
`w.pfE.org/pff/cad/patr051496.l1tn1l, printed Apr. 29, 1997, 8
`pages.
`Massey, Tim et al., “DSP Solutions for Telephony and
`Data/Facsimile Modems” Application Book, Texas Instru-
`ments SPRA073, copyright Texas Instruments, Inc., Jan.
`1997, pp. 1-102.
`“Procedures for Document Facsimile Transmission In The
`General Switched Telephone Network”, Fascicle VII.3—Rec.
`T.30, former Recommendation T.4, mar del Plata, 1968;
`amended and renumbered at Geneva, 1976 a11d 1980, Mala-
`ga—Torremolinos, 1984 and Melbourne, 1988.
`
`ANSI Technical Publication T1.413—1995, “Network and
`Customer Installation lnterfaces—Asymmetric Digital Sub-
`scriber Line (ADSL) Metallic Interface”, approved Aug. 18,
`1995, copyright American National Standards Institute, Inc.,
`New York, 1995, pp. 1-166.
`SGS—Thomson Microelectronics Technical Publication
`ST7544, Universal Modem Analog Front—End (UMAFE),
`published Jun. 1995, pp. 1-50.
`
`(List continued on next page.)
`Primary Examiner—Douglas W. Olms
`Assistant ExumirLer—Kenneth Vanderpuye
`Attorney, Agent, or Firm—Wilson Sonsini Goodrich &
`Rosati
`
`[57]
`
`ABSTRACT
`
`The present invention allows telephone subscriber loops
`carrying data traflic between computer systems to be
`switched to an alternative connection through a data
`network, thereby unloading data traflic fro111 the telephone
`network. The invention operates by means of a break switch,
`which selectively switches a plurality of subscriber loops
`between a central oflice switching system and a data net-
`work. The break switch is coupled to a concentrator which
`takes a plurality of inputs from the break switch and con-
`nects them to a smaller number of modems in a modem pool.
`The concentrator allows a subscriber line to connect
`to
`di erent types of modems within the modem pool, depend-
`ing upon requirements of a particular subscriber line user.
`The modem pool connects through a network interface to a
`packet-switched network, such as the Internet. Anumber of
`di ‘erent methods can be used to transmit a command to
`switch a subscriber loop from the central office switching
`system to the packet-switched network. A loop current
`detector, which is coupled between the plurality of sub-
`scriber loops and the break switch, can monitor on/o hook
`status of the subscriber loop in order to determine whether
`to switch the connection to the data network. Alternatively,
`the command to perform the switching can originate from a
`remote host which transmits the command through tie data
`network to the break switch.
`
`67 Claims, 6 Drawing Sheets
`
`120 ——
`SUBSCRIBER
`LOOPS
`
`210
`LOOP CURRENT
`DE] ECTOR
`
`220
`BREAK SW[TCH
`
`TO CENTRAL
`OFFICE SW|TCH[NG
`SYSTEM
`
`230
`ANALOG FRONT
`END
`
`240
`
`CONCENTRATORP
`
`280
`CONTROLLER
`
`260
`NETWORK
`I NTERFACE
`
`170
`PACKET-
`SWITCHED
`NETWORK
`
`Dish
`Exhibit 1014, Page 1
`
`

`
`6,091,722
`Page 2
`
`OTHER PUBLICATIONS
`
`Brownlie, J., “Draft Text of Recommendation V.8 (V.id)
`Proposed for Resolution 1, Point 8 Application at the Com-
`ing Study Group 14 Meeting In Jun. 1994”, International
`Telecommunications Union COM 14-10E, Mar. 1994, 10
`pages.
`
`Hawley, George T., “Systems Considerations for the Use of
`XDSL Technology for Data Access”, IEEE Communications
`Magazine, Mar. 1997, pp. 56-60.
`Forney, G. D., “The V/34 High-Speed Modem Standard”,
`IEEE Comm. Magazine, Dec. 1996, pp. 28-33.
`Stuart, R.L., International Telecommunications Union, Tem-
`porary Document 57-E, “Clean Final Draft of Recom1ne11-
`dation V34”, Geneva, Jun. 1-9, 1994, pp. 1-70.
`
`Dish
`Exhibit 1014, Page 2
`
`

`
`U.S. Patent
`
`0002on;1LuJ
`
`Sheet 1 of 6
`
`6,091,722
`
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`Exhibit 1014, Page 3
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`

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`U.S. Patent
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`0002on;1LuJ
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`Exhibit 1014, Page 4
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`Exhibit 1014, Page 5
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`

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`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 4 of 6
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`Exhibit 1014, Page 6
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`

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`U.S. Patent
`
`Jul. 18, 2000
`
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`Exhibit 1014, Page 8
`
`

`
`6,091,722
`
`1
`SUBSCRIBER LOOP BYPASS MODEM
`
`RELATED APPLICATION
`
`This application hereby incorporates by reference a
`related non-provisional application, entitled “Method for
`Bypassing Telephone Network,” by the same inventors,
`Donald M. Bellenger, James E. Dunn and Steven P. Russell,
`having serial number 08/819/874, and filing date Mar. 18,
`1997, which was filed on the same day as the instant
`application.
`
`5
`
`BACKGROUND
`
`1. I"ield of the Invention
`
`The present invention relates to systems for connecting
`telephone subscriber lines to computer networks, and more
`particularly to a system for switching a telephone subscriber
`line from a telephone central oflice switching system to a
`computer network.
`2. Related Art
`
`With the advent of computer networking and personal
`computers, public switch ed telephone networks (PSTNs)
`are increasingly used to connect computer systems to other
`computer systems, and to connect computer systems to
`computer networks, such as the Internet. This creates per-
`formance problems for PSTNs, because telephone line usage
`patterns for communications between computer systems are
`fundamentally different from telephone line usage patterns
`for voice connections. One problem arises because computer
`data calls often last much longer than voice calls, and
`telephone switching equipment cannot distinguish a data call
`from a voice call. Consequently, voice calls may be blocked
`due to the long holding times of data calls. Furthermore, data
`calls do not use the voice bandwidth efficiently. Most of the
`time, a data connection is not actually sending data, it is
`simply reserving the connection in case it might use it.
`PSTNs are designed to maximize trunking efliciency
`when only a small percentage of possible connections are in
`actual use at a given instant. Voice telephone calls typically
`last about three minutes, and during this time a guaranteed
`data transfer rate must be sustained. In contrast, communi-
`cations between computer systems, for example email, do
`not require a continuous transfer rate; interruptions in the
`flow of data which would render speech signals unintelli— ,
`gible are acceptable for many computer communications.
`Furthermore, existing PSTNs were designed assuming a
`lengthy set 11p time followed by a large amount of voice data
`being transferred. These assumptions do not work well for
`computer connections, where many smaller data transfers _
`are spread o11t through a longer session. The call set up time
`in a PSTN is very long relative to the length of the individual
`data transfers. In order to minimize latency caused by call
`set up time, most computer users leave their telephone
`connections off hook for the entire time of the session, which
`may last several hours. This problem is amplified by the fact
`that PSTNs typically bill a flat rate for residential services.
`Hence,
`there is no time—based cost
`for
`lengthy data
`connections, and no incentive to limit connection time.
`As PSTNs are increasingly used to support data calls
`between computer systems, th e long session times for data
`calls often degrades the performance of PSTNs. There is a
`problem with “switch holding time.” PSTN switches are
`designed for an average three minute holding time of a voice
`call. While data calls last much longer, averaging about
`eighteen minutes. The result is that switches begin to block
`because of the long-lived data connections, and additional
`
`2
`calls cannot be completed. This blocking unfortunately
`applies to all calls. Hence, ordinary voice telephone calls
`cannot be completed because they are blocked by data calls.
`One solution to this problem is to design a system around
`a device known as a POTS (Plain Old Telephone Service)
`splitter, which splits a signal on a telephone subscriber loop
`into two pieces; a higher-frequency data component which
`is routed through a data network, and a lower-frequency
`voice component which is routed through a central office
`switching system. However, a POTS splitter can11ot separate
`lower-frequency voice band modem signa ls from ordinary
`voice signals in order to route them through a data network.
`What is needed is an eflicient method of separating data
`calls from voice calls, so that data calls may be switched
`from a PSTN to a data network.
`
`SUMMARY
`
`invention provides an architecture and a
`The present
`method for switching a data call from a PSTN to a data
`network. In one embodiment, this switching is activated by
`a telephone li11e user, before a connection is made through
`a telephone central 0 ice switching system.
`In another
`embodiment, this switching is activated by a network ser-
`vice provider after a connection to the network service
`provider is established through a telephone central office
`switching system. The present
`invention allows lower-
`frequency voice band modem connections to be transferred
`to the data network as well as higher frequency broad band
`modem connections.
`
`the present invention can be characterized as a
`Thus,
`method for switching a subscriber loop between a central
`office switching system and a packet—switched network by:
`establishing a connection between the subscriber loop and a
`switch; receiving a command to switch the subscriber loop
`to the packet—switched network; and switching the sub-
`scriber loop to the packet—switched network.
`According to one embodiment of the present invention, a
`control signal to switch the subscriber loop is generated in
`response to a signal received through the subscriber loop.
`This signal is encoded in the loop current of the subscriber
`loop, and more particularly in the on/off hook status of the
`subscriber loop. “Off hook” refers to the flow of direct
`current as the result of a telephone battery being applied to
`a telephone instrument’s reduced ohmic impedance in an
`active voice transmission state. “On hook” refers to the
`absence of direct current flow from the telephone battery
`when the telephone instrument is in a high impedance idle
`state.
`
`the
`invention,
`In another embodiment of the present
`control signal is generated in response to a telephone num-
`ber dialed into the subscriber loop. This telephone number
`may be in the form of a dual
`tone multiple frequency
`(DTMF) signal, or a pulse dialing signal on the subscriber
`loop.
`According to another aspect of the present invention, the
`switch control signal is generated in response to a signal
`received through the central office switching system. This
`signal may originate from the central oflice switching sys-
`tem itself, or alternatively from a remote host which trans-
`mits the control signal to the switch through the central
`o ice switching system.
`The present invention can also be characterized as an
`apparatus for switching a plurality of subscriber loops
`between a central office switching system and a packet-
`switched network comprising: a network interface coupled
`to the packet—switched network; a plurality of modems
`
`Dish
`Exhibit 1014, Page 9
`
`

`
`6,091,722
`
`3
`coupled to the network interface; and a first switch coupled
`to the plurality of subscriber loops, the central office system,
`and the plurality of modems, for switching the subscriber
`loops between the central oflice switching system and the
`plurality of modems.
`According to another aspect of the present invention, the
`apparatus further includes a second switch coupled between
`the first switch and the plurality of modems comprising: a
`plurality of first switch interfaces coupled to the first switch;
`a plurality of 1node111 interfaces coupled to the plurality of
`modems; and a switching channel for selectively coupling
`first switch interfaces to modern interfaces.
`In one
`embodiment,
`there are n1ore first switch interfaces than
`modern interfaces, so that the second switch performs a
`concentration function by switching a number of subscriber
`lines into a smaller number of modems.
`
`The present invention can also be characterized as an
`apparatus for switching signals onto subscriber
`loops
`between a central office switching system and a packet-
`switched network, comprising: a first port coupled to a
`subscriber loop; a second port coupled to the central office
`switching system;
`a third port coupled to the packet-
`switched network, and a switch coupled to the first port, the
`second port and the third port, the switch responding to a
`control signal to switch the first port between the second port
`and the third ort.
`
`The present invention has a number of advantages. It
`effectively o ‘ loads long-lived data connections from a
`PSTN onto a data network. In doing so, it concentrates a
`number of subscriber loops into a smaller number of
`modems whica connect to the data network, so that a smaller
`number of modems can service a larger number of telephone
`subscriber loops. The present invention also allows tele-
`phone subscriber loops to be connected to a variety of
`different modern types, depending upon which modem type
`is required by a data user on a subscriber loop.
`DESCRIPTION OF THE FIGURES
`
`FIG. 1 is a block diagram illustrating how the bypass
`modem 130 of the present invention connects subscriber
`loops 120 to central 0 ice switching system 140 and packet-
`switched network 170 according to an aspect of the present
`invention.
`
`,
`
`FIG. 2 is a block diagram illustrating the basic functional
`components of a system to switch subscriber loops 120 onto
`packet—switched network 170 in accordance with an aspect
`of the present invention.
`FIG. 3 is a circuit diagram of loop current detector 210
`(from FIG. 2), for detecting current on a subscriber loop _
`within subscriber loops 120 in accordance with an aspect of
`the present invention.
`FIG. 4 is a circuit diagram of break switch 220 (from FIG.
`2), including circuitry for ring generation and for detecting
`incoming calls from the central office switching system 140
`in accordance with an aspect of the present invention.
`FIG. 5 is a circuit diagram of analog front end 230 (from
`FIG. 2), including subscriber loop interface circuitry and
`analog to digital converters in accordance with an aspect of
`the present invention.
`FIG. 6 illustrates the interior structure of concentrator 240
`
`and modern pool 250 (from FIG. 2) in accordance with an
`aspect of the present invention.
`DESCRIPTION
`
`The following description is presented to enable any
`person skilled in the art to make and use the invention, and
`
`4
`is provided in the context of a particular application and its
`requirements. Various modifications to the preferred
`embodiment will be readily apparent to those skilled in the
`art and the general principles defined herein may be applied
`to other embodiments and applications without departing
`from the spirit and scope of the invention. Thus, the present
`invention is not intended to be limited to the embodiment
`shown, but is to be accorded the widest scope consistent
`with the principles and features disclosed herein.
`FIG. 1 illustrates how subscriber loops 120 connect
`through bypass modem 130 to central oflice switching
`system 140 and packet—switched network 170 in accordance
`with an aspect of the present invention. FIG. 1 includes
`computer system 100, which is any type of computer system
`capable of receiving and transferring data. This includes
`computer systems as diverse as personal computers, main
`frame computers, and embedded system controllers.
`Computer system 100 connects to modem 110. Modern
`110 is any type of modern, including a high frequency broad
`band modem, such as a DSL, ADSL, XDSL, HDSL, SDSL
`or VDSL modern. Modem 110 can also be a lower frequency
`voice band modem, such as a v.34 or other voice band
`modem. Voice communications typically occupy a fre-
`quency range of 3(l0—3,400 IIz; signals approximately in
`this frequency range are referred to as “voice band” signals.
`Higher-frequency signals, up to approximately 1 MHZ, are
`referred to as “broad band” signals. Computer data calls are
`typically modulated on a carrier frequency. In the case of
`voice band modem communications, this carrier frequency
`is a lower-frequency voice band signal. In the case of broad
`band modem communications, this carrier frequency is a
`higher-frequency broad band signal. In contrast, regular
`voice signals are typically not modulated on a telephone
`subscriber loop.
`In another embodiment, modern 110 follows the v.34
`standard, but l1as a symbol rate in excess of the symbol rate
`specified in the v.34 standard.
`In a variation of this
`embodiment, modern 110 is implemented with a digital
`signal processor running code to implement
`the v.34
`standard, with a symbol rate in excess of the symbol rate
`specified in the v.34 standard.
`In one embodiment, modern 110 is built into computer
`system 100.
`In another embodiment, modem 110 exists
`independently from computer system 100.
`Tlypass modem 130 connects to central office switching
`system 140. Central office switching system 140 is a cen-
`tralized telephone switching system, which connects to a
`plurality of subscriber loops that extend from central office
`swi ching system 140 to telephone line users. This includes
`private automatic branch exchanges (PABXS), as well as
`swi ching systems found within telephone companies.
`Bypass modem 110 connects to subscriber loops 120,
`which carry electrical signals between bypass modem 110
`and central office switching system 140. If central office
`swi ching system 140 is a PABX system, such as those found
`within businesses and hotels, subscriber loops 120 may
`consist entirely of wiring within a building. If central office
`swi ching system 140 is located at a telephone company,
`subscriber loops 120 extend from subscriber equipment to a
`tele hone company switching system. Subscriber loops 120
`connect to bypass modem 130, which switches subscriber
`loops 120 between central office switching system 140 and
`pac <et-switched network 170.
`Central ofifice switching system 140 also connects to
`public switched telephone network 150, which routes and
`carries telephone signals between a plurality of different
`cen ral office switching systems.
`
`Dish
`Exhibit 1014, Page 10
`
`

`
`6,091,722
`
`5
`Public switched telephone network 150 connects to net-
`work service provider 160. Network service provider 160 is
`any type of system providing network access to computer
`systems. This includes commercial on—line services such as
`America On-Line and Con1puServe.
`Bypass modem 130 also connects to packet-switched
`network 170. Packet-switched network 170 is any type of
`network which transfers digital data;
`it
`is not limited to
`networks using a packet-switched protocol.
`In one
`embodiment, packet-switched network 170 is the Internet.
`However, any other networks for transferring digital data
`may be used.
`Packet-switched network 170 connects to network service
`provider 160, which provides facilities for connecting com-
`puter systems to packet-switched network 170, as well as
`other services used in conjunction with packet-switched
`network 170.
`
`The system embodied in FIG. 1 operates in the following
`manner. Bypass modem 130 is usually transparent. For
`telephone users making or receiving ordinary voice calls, the
`system operates as if the bypass device were not present.
`When a data call is initiated, bypass modem 130 springs into
`action. In one embodiment, a call is first placed through
`central o ice switching system 140 and public switched
`telephone network 150 to network service provider 160.
`Upon receipt of identification information from computer
`system 100, network service provider 160 sends a data
`packet via packet-switched network 170 to activate bypass
`modem 130. Bypass 111odem 130 has an Internet protocol
`address, and network service provider 160 sends commands
`directly to this Internet protocol address through packet-
`switched network 170. Upon receipt of an activation com-
`mand from packet-switched network 170, bypass modem
`130 disconnects a subscriber loop from central office switch-
`ing system 140 and establishes an alternate connection to
`network service provider 160 through packet-switched net-
`work 170.
`
`In the active state, bypass modem 130 supplies all of the
`POTS functions normally provided from central olfice
`switching system 140 to subscriber loops 120. This includes
`battery feed, overvoltage, ringing injection, supervision,
`codec, hybrid and testing functions. During the bypass
`period, any incoming calls from central office switching
`system 140 to the subscriber loop receives either a ring—no— ,
`answer signal, or alternatively a busy signal.
`According to another embodiment of the present
`invention, the control signal used to switch bypass modem
`130 is activated by an electrical signal on a subscriber loop.
`In one embodiment, this control signal is encoded in the loop _
`current status of the subscriber loop, and more specifically
`in the on/off hook status of the subscriber loop. In another
`embodiment, the control signal is encoded on a dual tone
`multiple frequency (DTMF) or pulse signal on a subscriber
`loop. Alternatively, any other ground start, loop start, or
`electromagnetic signaling method may be used. For
`example,
`in one embodiment
`the signal
`is encoded on
`autobaud modem signals as defined by CCITT Blue Book
`Series V or by CCITT v.34. In another embodiment,
`the
`signal is encoded on modern carrier tones, such as defined by
`ANSI Tl.4l3. These include the 34.5 kHz initialization
`tone;
`the 69 kHz upstream pilot
`tone and the 276 kHz
`downstream pilot tone. In another embodiment, the signal on
`the subscriber loop takes the form of a digital message
`encoded on the subscriber loop.
`According to another embodiment of the present
`invention, the control signal is activated by a signal which
`
`6
`travels through central oflice switching system 140. This
`signal may originate from network service provider 160, or
`alternatively, it may originate from a portion of the tele-
`phone system, possibly public switched telephone network
`150, or central office switching system 140.
`In another embodiment, the control signal is activated by
`a signal from packet-switched network 170. In one embodi-
`ment this signal originates from network service provider
`160. In another embodiment this signal originates from the
`telephone system. Alternatively, this signal may originate
`from any other source connected to packet-switched net-
`work 170.
`
`In one embodiment the control signal for the switch is
`activated by a single hook switch llash HSF). This embodi-
`ment operates as follows. The switch normally connects the
`subscriber loop to the voice network. In placing a voice call,
`the system operates as if the switch were not present. To
`activate the switch, the subscriber takes the line off hook,
`and then performs a short interrup ion of the loop current.
`Hook switch flash is defined as the following sequence: off
`hook, on hook, off hook. When the IISF is performed
`manually by a human, the initial o hook and on hook may
`vary in duration approximately between the limits of 40
`msec minimum, to a maximum 0 3 seconds. In another
`embodiment, which detects HSF signals from a computer,
`intervals of less than 30 msec are used. Another embodiment
`uses more than a single HSF to trigger a switching operation.
`It is assumed that there are two types of subscriber loops;
`voice band and broad band. For the voice band subscriber
`loops, any interruption in the subscriber loop current causes
`the switch to return the subscriber loop to the voice network.
`For broad band subscriber loops, the switch ignores discon-
`nect loop current status. Other embodiments use further
`disconnect methods,
`including internal
`timers, a ringing
`signal from the voice network, and other explicit disconnect
`signals sent through the subscriber loop and the data net-
`work.
`
`In another embodiment, the switch is activated by control
`codes dialed into a subscriber loop. For example, when a
`subscriber dials an ordinary telephone call to network ser-
`vice provider 160, network service provider 160 activates
`bypass modem 130 by sending explicit commands to bypass
`modem 130.
`
`In another embodiment, bypass modem 130 decodes the
`dialing signal on a subscriber loop and compares the number
`dialed with an internal table of numbers. If a match is found
`between the number dialed and a number stored in the table,
`the subscriber loop is switched from the voice to the data
`network. This number may be dialed in the form of a DTMF
`or pulse dialing signal. Bypass modem 130 monitors the off
`hook status of a subscriber loop. When the subscriber loop
`goes o ‘ hook, bypass modem 130 monitors what number is
`dialed into the subscriber loop and looks this number up in
`the table.
`
`FIG. 2 is a block diagram of the internal structure of
`bypass modem 130 (from FIG. 1) in accordance with an
`aspect of the present invention. Bypass modem 130 com-
`prises the following elements:
`loop detector 210, break
`switch 220, analog front end 230, concentrator 240, modem
`pool 250, network interface 260 and controller 280.
`Loop Current detector 210 connects to subscriber loops
`120 and break switch 220. Loop current detector 210 detects
`the loop current status, or other electrical signals, on sub-
`scriber loops 120. Electrical signals on subscriber loops 120
`pass through loop current detector 210 into respective inputs
`in break switch 220.
`
`Dish
`Exhibit 1014, Page 11
`
`

`
`6,091,722
`
`7
`Break switch 220 connects to central office switching
`system 140 (from FIG. 1) and to analog front end 230. Break
`switch 220 switches subscriber loops 120 between central
`oflice switching system 140 and packet—switched network
`170 through analog front end 230.
`Analog front end 230 provides battery, overvoltage,
`hybrid and supervision functions for subscriber loops 120.
`Analog front end 230 also connects to concentrator 240, and
`routes signals from break switch 220 into concentrator 240.
`Concentrator 240 additionally connects modem pool 250.
`Concentrator 240 switches a plurality of signals from break
`switch a 220 into a plurality of modems within modem pool
`250. In one embodiment, the number of inputs from break
`switch 220 is greater than the number of modems within
`modem pool 250. Concentrator 240 thereby performs a
`concentration function as well as a switching function.
`Modem pool 250 connects to network interface 260.
`Modems within modem pool 250 takes signals from con-
`centrator 240 and convert them i11to suitable format for
`transmission to network interface 260.
`
`Network interface 260 connects to packet-switched net-
`work 170, and routes signals from modems within modem
`pool 250 to packet-switched network 170.
`Controller 280 connects to loop current detector 210,
`break switch 220, analog front end 230, concentrator 240,
`modern pool 250 and network interface 260. Controller 280
`coordinates the operation of loop current detector 210, break
`switch 220, analog front end 230, concentrator 240, modern
`pool 250 and network interface 260. In one embodiment,
`controller 280 includes a microprocessor, such as the
`Motorola 860, and uses the microprocessor’s internal
`registers,
`timers and external dynamic RAM memory in
`performing the control functions.
`This RAM memory contains various tables including: a
`table relating subscriber loops to one or more data network
`addresses such as switched virtual circuit addresses, perma-
`nent virtual circuit addresses, or IP addresses; a data struc-
`ture for recording time since the last off hook condition was
`detected; a data structure for recording time since the last on
`hook condition was detected; a data structure for recording
`time since the ringing condition was detected; a data struc-
`ture for recording dialed number sequences; a table relating
`subscriber loops to a list of dialed number sequences; a table
`for translating from dialed number sequences to network .
`addresses; a table relating dialed number sequences to data
`network addresses, such as switched virtual circuit
`addresses, permanent virtual circuit ac dresses, or
`IP
`addresses; a data structure for recording cumulative activity
`per subscriber loop for accounting and billing purposes; a _
`data structure for recording overall switch activity across all
`subscriber loops in order to collect
`tra ic management
`statistics to determine utilization of the switch used and
`quality of service; a table relating subscriber loops to
`identification numbers; a table relating suascriber loops to
`one or more telephone numbers; and a
`able specifying
`allowable modem configurations,
`to control switching of
`subscriber loops by concentrator 240 to modems within
`modem pool 250.
`In one embodiment, controller 280 includes a mechanism
`by which the various tables and data structures in the RAM
`memory can be modified and read from a remote location.
`In a variation on this embodiment,
`the modification and
`reading take place in response to data sent over packet-
`switched network 170.
`Network interface 260 facilitates connections between
`modems in modem pool 250 and packet-switched network
`
`8
`170. In one embodiment, network interface 260 includes a
`Motorola 860 microprocessor and an Ethernet interface.
`FIG. 3 is a circuit diagram of a an embodiment of loop
`current detector 210 (from FIG. 2) FIG. 3 illustrates the
`circuitry for a single subscriber loop within subscriber loops
`120. The subscriber loop consists of two lines; subscriber tip
`300 and subscriber ring 302. Subscriber tip 300 passes
`through resistor 304 and feeds into opto-isolator 322 as well
`as 250 volt protection 310. Subscriber ring 302 passes
`through resistor 306 and feeds into opto-isolator 324 as well
`as 250 volt protection 310. 250 volt protection 310 addi-
`tionally connects to ground. Another terminal of opto-
`isolator 322 feeds into a respective input in break switch 220
`(from FIG. 2). Similarly, another terminal of opto-isolator
`324 feeds into a respective input within break switch 220.
`Opto-isolator 322 includes switching transistor 326 which
`connects an output “right” 322 to ground. Opto-isolator 324
`includes switching transistor 328 which connects an output
`“left” 334 to ground.
`Opto-isolators 322 and 324 consist of an LED and a
`transistor encased in a single package. One of the opto-
`isolators 322 and 324 indicates when current flows in one
`direction, and the other opto-isolator indicates when current
`[lows in the opposite direction. Opto-isolators 322 and 324
`are placed symmetrically in each path of the subscriber loop.
`In each case,
`the