United States Patent
`
`[19]
`
`[11] Patent Number:
`
`4,920,533
`
`Dufresne et a1.
`
`[45] Date of Patent:
`
`Apr. 24, 1990
`
`[541
`
`CATV SUBSCRIBER TERA/[DIAL
`TRANSMISSION CONTROL
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`[751
`
`Inventors: Michel Duh-eerie, Boucherville;
`Samir Sammouo, Brossard; Dave
`Gregory, Caigary; Jean-Paul
`Champagne, Binssard; Alain Tessier,
`Piedmont; Pierre Scott; Francois
`Methot, both of Montreal, all of
`Canada
`
`[73] Assignee: Videotron LTEE, Montreal, Canada
`
`[21} Appl. No.: 262,802
`
`[22] Filed:
`
`Oct. 26, 1988
`
`Foreign Application Priority Data
`
`[30]
`Nov. 2, 1981 [CA]
`
`Int. (:1.5 ............................................... HMN 7/08
`[51]
`[52} vs. C]. .................................. 370/852; 370/941,
`455/5; 358/86
`370/85, 89. 94, 124,
`[58] Field of Search
`sic/69.1, 123; 325/45, 46; 455/3, 4, 5, 6;
`340/8255; 358/84, 86; 380/10, 20
`
`.................... 455/5
`8/1985 McNamara et a1.
`4,533,948
`.. 370/85
`8/1985 Kume etai.
`4,536,875
`1.. 358/86
`4,553,161 11/1985 cam
`380/10
`4,623,920 11/ 1986 Dufresne et al.
`.. 358/84
`4,752,954 6/1988 Masuko
`4,773,065
`9/1988 Kobayashi etal 310/85
`
`
`
`..
`
`Primary Examiner—Douglas W. Olms
`Assistant Exomfner—Alpus H. Hsu.
`Attorney, Agent, or Firm—Antoneili, Terry & Wands
`
`[57]
`
`ABSTRACT
`
`A bidirectional cable communication system compris-
`ing a head and, a bidirectional transmission network
`connected to the head end for transmitting signals
`downstream from the head end to a plurality of sub-
`scriber stations and for transmitting data signals up-
`stream to the head end from the subscriber stations,
`means at the head end for detecting collisions between
`signals received from the subscriber stations and for
`generating a collision signal, means at the head end for
`transmitting downstream on the transmission system
`status bits of data signal indicative of the collision,
`whereby upon detection thereof by a subscriber station
`it can be enabled to cease transmission.
`
`30 Claims, 6 Drawing Sheets
`
`
`
`
`
`
`
`
`
`
`
`SUBSCRIBER
`TEEMIHAL
`
`
`mils/Him?
`
`EXHIBIT
`
`Ex. 1009
`
`Page 1 0f 16
`
`PETITIONER‘S EXHIBIT 1009
`
`Page 1 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`US. Patent
`
`Apr.24,1990
`
`Sheet 1 of6
`
`4,920,533
`
`
`
`
`
`FIG. 1
`
`TERMINATION
`
`Page 2 0f 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 2 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`us. Patent
`
`'Apr.24,1990
`
`Sheet 2 on
`
`4,920,533
`
`23
`
`22
`
`TV TUNER!
`FILTER FILTER
`ANALOG CIRC 011'
`
`
`DIGITAL.
`DEMO}; ULATOR —_
`
`MODULATOR
`
`
`
`DIV.BYN -.
`
`_MEOUT
`
`“WON
`
` _ODULATOR
`_1S: F2)
`LOGIC
`29
`
`
`
`
`
`OTHER
`
`DIGITAL
`cmcurrs
`
`
`
`Fig. 4
`
`
`
`_ROCESSOR
`
`MEDIA ACCESS
`MOMENT
`TRANSMIT
`1C
`
`
`
`STARTFRAME
`DELIMITER
`
`SOURCE
`ADDRESS
`
`LENGTH OF
`FRAME
`
`WCHECK
`SEQUENCE
`
`
`PREAMBLEDES‘I‘INA’I‘ION ADDRESS
`' Fig ' 3
`
`WUWHWUW -----
`‘9
`1\3
`19
`I];
`19
`>3
`19
`
`Fig. 2
`
`Page 3 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 3 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`US. Patent
`
`Apr. 24, 1990
`
`Sheet 3 of 6
`
`4,920,533
`
`Ersa-
`BEEE
`E:E
`
`FIG.5
`
`Page 4 0f 16
`
`'
`
`PETITIONER'S EXHIBIT 1009
`
`Page 4 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`US. Patent
`
`Apr. 24, 1996
`
`Sheet 4 of 6
`
`4,920,533 '
`
`
`
`PROBAB[LITREGISTER
`
`m
`
`LL!.4
`
`Ql
`
`:III
`:-
`m3
`
`Page 5 0f 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 5 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`US. Patent
`
`Apr. 24, 1990
`
`Sheet 5 of6
`
`4,920,533
`
`nusvBIT
`
`IDLE
`
`FIG7A
`
`l'F
`'
`
`TRONJO
`
`73
`
`Hmm
`
`b
`
`0
`
`:i
`
`1'6
`
`L
`
`
`
`
`Page 6 0f 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 6 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`US. Patent
`
`Apr. 24, 1990
`
`Sheet 6 of 6
`
`4,920,533
`
`FIG.7B
`
`Page 7 0f 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 7 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`1
`
`4,920,533
`
`2
`rate downstream data channel. The signals in the data
`channel are transmitted in packets divided into time
`slots, the time slots being separated by a special byte of
`data referred to herein as a status byte. The status byte
`is formed of bits which are referred to herein as “busy
`bits”.
`The downstream data signal is frequency
`multiplexed with the TV signals, using a separate
`channel, and is transmitted downstream through the
`network to the subscriber terminals. The subscriber
`terminals each detect the busy bits and after decoding,
`determine whether the network is
`idle, busy, or
`whether a collision has occurred and if desired, a prior-
`ity level. Each subscriber terminal if it has data to trans-
`mit. transmits back to the head end, with a certain prob-
`ability factor. The probability factor is modified de-
`pending on whether the busy bits which the terminal
`continuously receives indicates a collision (which indi-
`cates that another subscriber terminal has transmitted,
`polluting its data signal). If a collision is detected, the
`probability factor is changed, and the subscriber termi-
`nal retransmits the data from the time slot which has
`been polluted at a time dependent on the probability
`factor.
`The transmitting subscriber terminal also counts col-
`lisions,
`i.e. the number of collisions indicated by the
`busy bits. If the number of collisions is in excess of a
`predetermined threshold,
`it recycles the probability
`factor and retransmits the entire data sequence at a time
`which is controlled by the new probability factor.
`Any subscriber terminal is inhibited from transmit-
`ting if the busy bits which it receives indicate that the
`network is busy in the upstream direction. Thus the
`collision effect occurs following the time that the busy
`bits indicate that the upstream data channel is idle, data
`has begun to be transmitted by more than one subscriber
`terminal, and prior to the time that subscriber terminals
`receive busy bits from the head end which indicate that
`the upstream channel has been seized, i.e. is busy. Thus
`the collision effect occurs typically at the initiation of a
`new transmission by more than one subscriber terminal
`when the channel is idle,
`increasing with increasing
`traffic.
`The probability of transmission factor is varied using
`a random number generator, which, coupled with the
`likelihood of different time delays for signals transmit-
`ted from the various subscriber terminals within the
`system, decreases thellikelihood that more than one
`would transmit at the same time, than if the probability
`factor was varied in the same way at each subscriber
`terminal Further, since the number of collisions causes a
`decreased probability that a subscriber terminal is al-
`lowed to transmit, the heavier the traffic, the more the
`likelihood that a subscriber terminal is automatically
`caused to wait for a longer random period to transmit.
`The system thus automatically compensates and adjusts
`for increased traffic.
`The problem of noise gathering is substantially solved
`by causing each subscriber terminal to transmits its data
`using frequency shift keying at two spaced frequencies,
`and by using a narrow band filter, having two passbands
`just sufficient to pass the two frequencies, in the up-
`stream direction in each branch of the network. The
`downstream data signals are unaffected The filters thus
`block virtually all noise except a small amount in the
`two narrow passbands from passing upstream to the
`head end. The filters are preferably remotely address-
`able so that they can be controllably switched to pass
`
`CATV SUBSCRIBER TERNIINAL TRANSNHSSION
`'
`CONTROL
`
`This invention relates to a bidirectional transmission
`system, and particular to one in which many subscriber
`stations can transmit data signals upstream to a head
`end.
`
`Cable transmission systems typically carry various
`TV signals downstream in a tree-type network contain-
`ing a main trunk and branches from the trunk, with
`subscriber terminals connected to drops via splitters to
`the branches. Typical networks are fabricated of coaxial
`cable, with repeater amplifiers spaced along the net-
`work to maintain the signals to be distributed above a
`predetermined minimum level.
`It has been an objective to allow signals to be origi-
`nated at the subscriber terminals for transmission up-
`stream to the head end as requests for service, for selec-
`tion of programs, responses to polling, etc. However
`various problems as will be described below have pro-
`hibited successful provision of services whereby signals
`could be originated at the subscriber terminals. passed
`upstream through the network, to the head end. Conse-
`quently such systems have utilized a separate transmis-
`sion network, e.g. telephone system or only pseudo-
`interactive systems in which all programs or informa-
`tion signals are presented to the subscriber terminals
`and the programs or information are selected at the
`terminals. In both cases the signals originating at the
`subscriber terminals are not passed upstream in the
`system.
`Two very significant problems prohibited successful
`two-way communication Via the same CATV network.
`With typically thousands of subscriber terminals having
`the possibility of transmitting upstream within the same
`frequency band, there is a significant likelihood that
`several might be transmitting at the same time. The
`result at the head end is pollution of the signals received
`from one subscriber terminal by signals received from
`other simultaneously transmitting subscriber terminals.
`The problem is made worse by the existence of various
`time delays withimthe system presented to the signals
`transmitted from various subscriber terminals due their
`locations being at various different line lengths (trans-
`mission distances) from the head end.
`The second problem involves noise gathering. It will
`be appreciated that significant upstream noise is gath-
`ered from the various branches feeding into a single
`trunk, which noise often can be significantly higher
`than the signal level transmitted by a single subscriber
`terminal The problem is increased with the use of two-
`way amplifiers in the system, those amplifying in the
`upstream direction attempting to amplify whatever
`signals are applied to their inputs, e.g. noise. Such am»
`plifiers typically use automatic gain controls, which
`operate with maximum gain at the time of minimum
`signal, thus outputting maximum noise collected from
`all branches feeding into that amplifier.
`The present invention is a cable transmiSsion system
`which substantially reduces or eliminates the problem
`of collisions between signals from various subscriber
`terminals arriving at the head end at the same time. Also
`disclosed is means for substantially reducing or elimi-
`nating the problem of noise gathering.
`The head end in the cable system of the present in-
`vention provides television signals as in a normal
`CATV system, but also transmits data signals in a sepa-
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`6t}
`
`65
`
`Page 8 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 8 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`4,920,533
`
`3
`signals or upon receipt of an upstream signal. It has been
`found that this structure successfully inhibits noise gath-
`ermg.
`The prior art problems of collision of upstream sig-
`nals in a bidirectional cable communication system and
`noise gathering are thus substantially overcome
`Briefly, the invention is a directional cable communi-
`cation system comprising a head ad, a bidirectional
`transmission network connected to the head end for
`carrying signals downstream from the head end to a
`plurality of subscriber stations and for carrying data
`signals upstream to the head end from the subscriber
`stations. A circuit at the head end detects collisions
`between signals received from the subscriber stations
`and generates a collision signal, and a further circuit at
`the head end transmits downstream on the transmission
`system a status byte of data signal indiCative of the
`collision, whereby upon detection thereof by a sub-
`scriber station it can be enabled to cease transmission.
`Preferably the head end collision detector also in-
`cludes apparatus for detecting whether or not signals
`are being received from any subscriber station and for
`generating a busy or idle status byte signal respectively,
`the byte transmitting circuit generating the byte of data
`signal indicative of the collision, the idle, or the busy
`status.
`
`It is also preferred that the status byte of data should
`be transmitted separating time slots of a downstream
`data signal, in which a maximum round trip propagation
`trip delay, being the sum of the delays of all components
`in the transmission loop to the longest delayed end of
`the network in both downstream and upstream direc
`tions, defines the time period between successive status
`bytes which should be at least as long as said propaga—
`tion delay.
`The invention is also a subscriber terminal for use in
`a bidirectional cable communication system comprising
`apparatus for repetitively receiving a data signal from a
`bidirectional transmission network comprised of a sta-
`tus byte indicative of the status of the network including
`signal collision, busy or idle, and preferably priority,
`apparatus for formulating and storing a data signal to be
`transmitted via the, network to the head end, apparatus
`for transmitting the data signal to the head end via the
`network, apparatus for controlling the apparatus for
`transmitting, the apparatus for controlling comprising
`apparatus for receiving the status byte and for enabling
`transmission of the data signal with a predetermined
`probability P, apparatus for counting the number of
`signal collision status signals received and for adjusting
`the probability P in accordance therewith.
`It is preferred that the apparatus for controlling inhib-
`its transmission for a period of time if the number of
`signal collision status signals received exceed a prede-
`termined maximum, thereupon reinitiating retransmis-
`sion of the complete data signal.
`A better understanding of the invention will be ob-
`tained by reference to the detailed description below of
`a preferred embodiment. with reference to the follow-
`ing drawings, in which:
`FIG. 1 is a block diagram of a bidirectional cable
`communication network in accordance with the inven-
`tion,
`FIG. 2 illustrates the downstream data stream with
`lime,
`FIG. 3 illustrates a data packet with time,
`FIG. 4 is a block schematic of a subsoriber terminal in
`accordance with the invention,
`
`4
`FIG. 5 is a block diagram of the extraction logic
`circuit shown in FIG. 4-,
`FIG. 6 is a block diagram of the media access circuit
`shown in FIG. 4, and
`FIG. 7A and 713 form a schematic of the control
`transmitter at the subscriber terminal.
`FIG. 1 illustrates a bidirectional cable communica-
`tion network in accordance with the present invention.
`However it should be noted that the invention could be
`used in a star type network, a local area network or
`other kinds of networks. In the present embodiment. a
`system is comprised of a head end 1 which communi-
`cates via a wideband communication medium such as a
`coaxial cable 2 with a plurality of subscriber terminals 3.
`The terminals and head end 1 communicate via a net-
`work, such as a well known tree network, but could be
`another form of non-looping network. The tree net-
`work is comprised of bidirectional amplifiers 4 and
`splitters 5 which are connected via drops (not illus-
`trated) to the subscriber terminals. The network is ter-
`minated at a matching impedance 6 in a well known
`manner.
`
`For ease of description only one subscriber terminal 3
`has been shown However it should be clear that sub-
`scriber terminals can be connected to splitters distrib-
`uted along the network in a well known manner.
`In a conventional network, amplifiers 4 will be unidi-
`rectional in the downstream direction, whereby they
`carry a plurality of television channels. The present
`invention, however, is directed to the class of networks
`which also carry data signals. Such signals have been
`provided in networks which carry data signals which
`are to be reconstructed into computer generated pic-
`tures, computer programs, control signals for descrarn-
`blers, etc. Such data signals are sometimes carried in the
`vertical interval of a television channel, but in the pres-
`ent invention they are carried by a separate high speed
`data channel. Consequently the amplifiers 4 should
`have the capability of transmitting the data channel in
`the downstream direction.
`the subscriber
`In order to order specific services,
`terminal 3 typically has a keyboard which generates
`signals, ultimately resulting in command or other data
`signals to be transmitted upstream to the head end.
`Several problems have characterized this upstream
`transmission, with the result that few, if any such practi-
`cal systems exist. The present invention provides means
`for reliably transmitting data upstream from a large
`number of' subscriber tenninals. It should be noted,
`however, that bidirectional amplifier 4 should also have
`the capability of transmitting the data signals received
`from the subscriber terminals in the upstream directiou.
`Such amplifiers exist and the present invention is not
`specifically directed to them.
`Problems associated with upstream transmission in»
`clude noise gathering and data collisions. Noise gather—
`ing involves the generation of noise from the many
`branches of e.g. the tree network, which all feed into
`the main trunk or port of the system. The noise is ampli-
`fied by each of the amplifiers. resulting in a noise level
`at the head end which is excessive.
`Data collisions exist when more than one subscriber
`
`terminal transmits data signals in the upstream direction
`which arrive overlapping in time at
`the head end.
`Clearly this causes corruption of all data signals which
`overlap.
`The solution to the problem of avoidance of noise
`gathering is not the subject of the present invention. In
`
`10
`
`[5
`
`20
`
`25
`
`30.
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Page 9 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 9 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`4,920,533
`
`6
`The busy bits preferably are sent through the down-
`stream channel at 4 M bits per second periodically at the
`beginning of each time slot, as shown in FIG. 2 which
`illustrates the downstream data stream with time. The
`busy bits illustrated by arrows 18 therefore define the
`dine period of each time slot. The time slots can be
`programmed at the head end each containing e.g. 128,
`256, 512, 1024 bits, for example, the bit duration now
`preferably being 0.25 microseconds. The downstream
`data sent within the time slot is indicated as reference
`19.
`The communication controller also ensures that
`downstream data packets are not transmitted during a
`busy or collision state of the network. It also switches
`off the transmitter if it transmits for too long a period,
`e.g.
`if it
`transmits over a predetermined maximum
`packet size. The transmitter is thus locked and timed
`out.
`
`10
`
`15
`
`5
`the present invention the problem of collisions is solved,
`by the use of so-called “busy bits” which are transmit-
`ted from the head end downstream to the subscriber
`terminals. A byte of two busy bits defines the busy or
`idle quality of the channel. The two bits can of course
`define four different states, i.e. idle, busy, collision and
`a fourth state which can be used as a priority indicator
`or other information. However other number of busy
`bits can be used if desired.
`In general, the head end transmits on a regular basis,
`busy bits indicatinq an idle channel, preferably using
`AM modulation of a courier. If it receives data signals,
`it changes the character of the busy bits to define a busy
`condition. Upon analysis of the data, the head and de-
`tects collisions between received data signals, and if it
`detects such collisions, it changes the busY bits to indi-
`cate a collision condition.
`The subscriber terminal, on the other hand, transmits
`the upstream data, preferably in a frequency shift keyed
`form (eg FSK) It constantly monitors the downstream
`busy bits, and transmits when the channel is indicated as
`being idle (assuming that there is some data to transmit).
`If, while transmitting, it detects collisions between busy
`bits, it stops transmitting, waits for a period of time as
`will be described below, and then retransmits the signal.
`In order to minimize noise on the trunk filters 7 are
`connected in series with various branches of the distri-
`bution network, each filter having sharply defined nar-
`row bandpasses for the upstream frequency shift data,
`each filter being connected in the transmission upstream
`direction. This reduces all upstream noise except that
`which is in the bandwidth of the filter. To improve the
`upstream data transmission performance preferably
`filters are used which will remain shut off until they
`sense the presence of upstream carrier signal in the
`actual bandwidths of the filter, whereupon they will
`quickly open; e g. within microseconds, allowing the
`upstream data signal to pass. In addition, the filters
`could be addressable from the head end to cpen and
`close, for network mamrenance purposes. The filters are
`transparent in the dowmtream direction; the television
`signals and downstream data signals pass through these
`filters'1n the downnstream direction.
`Within the head end a source of television signals'is
`connected to a modulator 8, which has its output con-
`nected through channel filters 9 to the coaxial cable.
`Television signals are thus applied to the network as in
`the prior art.
`Receive bandpass filter 10 has its input connected to
`the coaxial cable 2, and its output to a data demodulator
`11. The frequency keyed data transmitted from sub-
`scriber terminal 3 thus is output from demodulator 11.
`Also connected to the output of filter 10 is a collision
`detector 12. Collision detector 12 detects the presence
`of overlapping bits preferably by means of envelope
`detection. Since that type of collision detection must be
`very fast, it is preferably done in broadband.
`Logic within collision detector 12 also provides the
`pair of bits which is referred to herein as the busy bits,
`designating the four states referred to above, idle, busy,
`collision and priority or undefined. These bits, desig-
`nated as [BC or channel state indicator are applied to a
`communication controller 13. Here the busy bits are
`interleaved (multiplexed)
`into a downstream data
`stream, which is applied to modulator 3. Modulator 8
`applies the combined data stream into a high speed data
`channel, from which the output is treated as described
`earlier with reference to the television signal sourCe.
`
`20
`
`25
`
`It is important that the period of time that separates
`the transmission event of consecutive pairs of busy bits
`should be equal to or greater than the maximum round
`trip propagation delay of the network. This delay is the
`sum of the delays of all of the components which consti-
`tute the transmission loop with maximum cable length,
`going first to the longest delayed end of the network, in
`both directions.
`
`Each data packet sent from the head end should pref-
`erably also be equal to or longer than one time slot
`period. A typical packet format is shown graphically in
`FIG. 3; it can be formed for example by a 2—7 byte
`preamble, followed by a one byte start frame delimiter
`followed by a 4 byte destination address, followed by a
`4 byte source address, followed by a two byte frame
`length indicator, followed by an indeterminate number
`of bytes containing the data to be transmitted, following
`by an indeterminate number of padding bytes (if neces-
`sary), followed by a two byte frame check sequence
`Turning now to FIG. 4, a block diagram of the pre-
`ferred form of subscriber terminal 3 shown in FIG. 1 is
`illustrated. Coaxial cable 2 from the network is con-
`nected to both downstream bandpass filter 22 (which is
`similar to filter 9) and upstream bandpass filter 23, the
`latter of which can form two narrow passbands just
`sufficient to pass the two frequencies of the frequency
`shift keyed modulated output signal to be generated in
`the subscriber terminal
`
`The output of filter 22 is carried via splitter 23A to
`TV tuner/analog circuit 24. Circuit 24 may consist of a
`tunable down-converter, pay TV descrambler or the
`like. The output of the circuit 24'1s applied to modulator
`25 for application to a TV set 26.
`The output of filter 2215 also connected via splitter
`23A to the input of a digital demodulator 27, which
`demodulates the data stream in the digital channel.
`Digital demodulator 27 provides data and clock output
`signals on correSponding output lines, in a well known
`manner. These signals are applied via a CAD circuit 8
`where they are translated into parallel in a known man-
`ner, and applied to data and clock inputs of a central
`processor/memory circuit 29. A data and address bus
`30 communicates with the central processing unit/-
`memory circuit 29. Other peripheral digital circuits 3!
`associated with the subscriber terminal are also con-
`nected to the central processing unit/memory circuit
`29, e.g. to control a video display generator, to monitor
`alarm circuits, etc.
`The data and clock lines output at the digital demod-
`ulator are also connected to corresponding inputs of
`
`35
`
`45
`
`SO
`
`55
`
`65
`
`Page 10 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 10 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`4,920,533
`
`7
`busy bits (IEC) extraction logic circuit 32. which is also
`connected to bus 3|). A divide by N circuit 33 is con—
`nected to the clock line, its output being a clock signal
`C]. The divide by N circuit thus generates un internal
`clock signal Cl from the clock line, and is thus desired
`from the downstream data signal.
`A. buffer 34 is connected to the bus 30, for receiving
`data signals from processor circuit 29 for transmission
`to the head end. The output of buffer 34 is connected to
`frequency shift key modulator 35. for modulating the
`output signal from buffer 34 into a frequency shift keyed
`signal within the passband of the upstream data channel.
`The output of modulator 35 is applied through a time
`out circuit 36 which controls the transmission interval
`of the upstream signal. The output of time out circuit 36
`is applied to upstream bandpass filter 23, from which it
`is applied to coaxial cable 2 for transmission to the head
`end.
`
`A media access management transmit logic circuit 3'!
`(MAC) (controlling means) is connected to bus 30, and
`has other inputs connected to the extraction logic cir—
`cuit 32 for receiving the busy bits. The MAC circuit is
`also connected to a control input of buffer 34 and to a
`control input/output of time out circuit 36. The purpose
`of the MAC circuit 37 is to detect the busy, idle or
`collision status of the network by monitoring the busy
`bits, and to control the transmission and the timing of
`the transmission of signals stored in buffer 34 to the
`head end.
`The digital channel signals are received from the
`head via cable 2, are filtered in filter 22 and are applied
`to digital demodulator 27. The resulting data and clock
`signals are applied to processor 29. A keypad or other
`means operating through other digital circuits 31 com—
`municates with processor 29 to cause it to formulate
`data signals for transmission to the head end. The mech-
`anism for formulating these signals in the CPU/memory
`is not the subject of the present invention as techniques
`known to persons skilled in the art can be used. Suffice
`to say that once the signals are formulated, they are
`passed via bus 3|) to the input of buffer 34 where they
`are stored.
`.
`The IEC extraction logic circuit 32 detects the busy
`bits on the data and clock lines at the output of demodu-
`lgor 27. The busy bits are presented to the MAC circuit
`MAC circuit 31 operates using an internal algorithm
`to be described below If the MAC circuit receives busy
`bits which indicate a busy channel or a collision, it waits
`until the arrival of the next busy bits, and continues
`monitoring the busy bits state. If the busy bits indicate a
`free channel, the MAC circuit decides to transmit with
`a probability P, or decides not to transmit with a proba-
`bility (l—P) and thus will wait until the arrival of the
`next set of busy bits whereupon it will operate of a
`probability of transmission adjusting algorithm.
`The MAC circuit upon deciding to allow transmis-
`sion. applies a control signal to buffer 34, which causes
`it to begin outputting its stored packet At the same time
`the MAC circuit monitors the busy bits. If the busy bits
`received, while the circuit is transmitting, indicate colli-
`sion. which means that one or more other transmitters
`are transmitting during the same time period, it immedi-
`ately controls buffer 34 to halt its transmission A colli-
`sion counter is also incremented within the MAC cir-
`cuit.
`If the number of collisions indicated on the collision
`counter exceeds a predetermined maximum, the enitre
`
`packet transmission process is stepped. The packet is
`returned to the buffer 34, where it waits a period of time
`prior to transmission again as controlled by the MAC
`circuit.
`If the number of collisions already occurred is less
`than the maximum, the packet transmission probability
`P is reduced by a factor K (where P=P/K) to a mini-
`mum retransmission probability value Then it waits
`until the next pair of busy hits at which time it repeats
`the examination of the next set of busy bits.
`If the next pair of busy bits does not indicate a colli-
`sion, it will necessarily indicate a busy state, since the
`subscriber station itself is transmitting. This means that
`the local subscriber terminal has uniquely captured the
`channel. Transmissiou is reinitiated and continued until
`the end of the packet, after which the channel will be
`declared free. The collision counter is then initialized to
`zero, and its transmission probability P to 1.
`The extraction logic circuit 32 and MAC circuit 37 of
`FIG. 4 will now be described in detail. Turning to'FIG.
`5, the busy bit extraction logic 32 circuit is shown in
`block diagram. The data and clock lines are connected
`to a descrambler circuit 40, for descrambling if neces-
`sary, if the downstream data signal has been received
`scrambled. Descrambler 40 is a mirror image circuit of
`the head end scrambler, which can be included as part
`of communication controller 13 (FIG. 1). The output
`signals of descrambler 40 are clock and data signals
`which are applied to the data and clock inputs of bit
`counter 4-1. Counter outputs of bit counter 41 are con-
`nected to flag determining circuit 42, which determines
`the beginning of a packet from the contents of counter
`41, and provides on its IND output a pulse or leading
`edge of a pulse which indicates the presence of the
`beginning of a received data packet.
`The data and clock outputs of bit counter 41 are
`connected to zero extraction'circuit 43. This circuit is
`used in a well known manner to remove zeros which
`may have been inserted in the communication control-
`ler 13 at the head end to distinguish the value of long
`bytes which all consist of ones. Thus zero extraction
`circuit 43 reconstitutes the original data. This corrected
`data is applied to a status byte extraction circuit 44.
`The corrected data signal is also applied to a counter
`and interval control circuit 45, which is connected via
`address bus ADDR and data bus DII|--D‘il to bus 30.
`Bus 30 is, as described earlier connected to processor
`29. The time slot interval is determined by the CPU and
`stored in its memory, and this data is sent via the bus 30
`to circuit 45 which in turn presents a control signal on
`the CTRL line to extraction circuit 44. The time slot
`can be found by changing the interval on the extractiOn
`circuit until the received packet check sum matches.
`Extraction circuit 44, which can be a programmable
`register, thus can receive the data within a time slot and
`provide the bits associated with the time of the busy or
`status bits to its output terminals. Those output termi-
`nals are connected to a decode IEC circuit 46, which is
`a two bit decoder, for decoding the busy bits. The four
`output terminals of decode IEC circuit 46 thus reflect
`the four states of the two bits constituting the busy or
`status bits: idle, busy, collision state, and a priority or
`other fourth state, which terminals are correspondingly
`labelled in FIG. 5. The lines connected to those termi-
`nals are connected to the MAC circuit 37.
`Turning now to FIG. 6, media access circuit 3'! is
`shown within the dashed lines in block diagram, along
`with additional details of circuits already shown.
`
`10
`
`15
`
`20
`
`25
`
`3D
`
`35
`
`4t)
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Page 11 0f16
`
`PETITIONER'S EXHIBIT 1009
`
`Page 11 of 16
`
`PETITIONER'S EXHIBIT 1009
`
`

`

`9
`The busy bit extraction circuit 32 is shown having its
`data and clock inputs connected to the output of digital
`- demodulator 27 reproduced from FIG. 4. Its output
`leads idle, busy, collision and priority are connected to
`the input of a transmitter control 51. The clock input to
`busy bit extraction circuit 32 is also connected to an
`input of the transmitter control 51. The address and
`control leads of bus 30 are connected to an address
`decoder 52,
`the decoded output thereof being con-
`nected to transmitter control 51. The data leads DIJ—