An Evolutionary Approach to the
`Development of Two-Way Cable
`Technology Communication
`
`JAMES B. WRIGHT
`
`Rockford Cablevision, Inc.
`
`MARTIN P. BLOCK
`
`D. STEVENS McVOY
`
`Michigan State University
`
`Broadband Technologies, Inc.
`
`While community antenna television (CATV)
`has continued a pattern of steady growth,
`the
`"blue—sky" promises of a cable revolution have
`yet to be realized. Despite the Federal
`Communications Commission rule requiring tech-
`nical capacity for nonvoiee return communication,
`two-way CATV has really not progressed much
`beyond the experimental stage.
`A combination
`of four factors are responsible for the slow
`development. First is the lack of credibility
`in the cable industry surrounding two-way CATV,
`due largely to some early over—zealous specu-
`lation and over-selling of the two-way CATV
`concept before the technology could deliver.
`Second is the inability of two-way CATV to
`attract adequate financial resources, creating
`the familiar "chicken or egg" problem. That
`is, without the financial support the technology
`cannot be developed, and without demonstrated
`technological promise the financial support
`cannot be generated. Other conditions
`contributing to the financial problem include
`the recent recession, high interest rates, and
`industry overexpansion. Third is restrictive
`governmental regulation which requires perfor-
`mance levels and services that contribute to
`higher operating costs and at the same time
`limits the entertainment fare, which reduces the
`potential revenue.
`The profit squeeze would
`limit interest in developing new services, as
`well as making the industry less attractive for
`investment purposes.
`Fourth are technical
`problems in the development of two-way CATV such
`as radio frequency interference and the design
`of a relatively inexpensive home terminal.
`
`While the outlook for two-way CATV does not
`seem particularly bright, a few recent events
`keep the promise alive.
`The National Science
`Foundation has made a large funding comitment
`to experiments in public service applications of
`the two-way technology. This will advance both
`the technology and our knowledge of potential
`applications. Secondly,
`the per-program pay
`television system in Columbus, Ohio has been a
`commercial success.
`In development of the
`Columbus system a number of technical and cost
`_problems have been solved. These events, which
`will be discussed here in some detail, provide
`solid evidence that two-way CATV can be developed
`despite the apparent problems.
`
`To assure this development, a systematic
`approach is needed which carefully times and
`integrates the technical capability with eco-
`nomically viable communication applications on
`a step-by—step evolutionary basis. This paper
`is an attempt to provide an outline of an
`evolutionary process which is believed to be
`feasible.
`It will begin with a description of
`the particular communication capabilities and
`potentials of a CATV system.
`
`Communication Capabilities of CATV
`
`A CATV system, by its physical nature, is
`most efficiently used as a means of dissemi-
`nating information from a single point, or
`source,
`to a large number of points, or users;
`and conversely it may also be efficiently used
`as a means of acquiring information from a
`large number of remote sources and transporting
`it back to a single point.
`A CATV system is
`used least efficiently in point-to—point
`communications.
`It is because of this unique
`characteristic of a CATV system that most
`discussion of two-way CATV is in terms of a
`digital return system generated by push-button
`response pads.
`
`Despite the popular characterization of
`CATV as the television of abundance,
`there is
`a very real limit to the available bandwidth
`in a cable system.
`The use of any available
`frequency must be considered in terms of both
`opportunity cost and the cost of additional
`equipment necessary to support it. This demands
`careful planning and spectrum management.
`
`A typical CATV system resembles a tree,
`with a network of trunk cable and trunk
`amplifiers delivering signals from the headend
`or transmission center to bridger amplifiers.
`These amplifiers then transfer the signal to a
`system of feeder cable and feeder amplifiers.
`The feeder system delivers the signal to the
`tap-off units, and then by service drops into
`
`in Rockford,
`Funding for the experiment
`Illinois, described in this paper and in which
`all three authors are associated, was provided
`by the National Science Fbundation. Director
`of the project, Thomas Baldwin, contributed
`substantially to the paper.
`
`52
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`IEEE TRANSACTIONS ON CABLE TELEVISION, VOL. CATV-2, NO. 1, JANUARY 1977
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`The return problem of
`the subscriber's home.
`noise and interference is most severe in the
`feeder and drop portion of the cable system.
`Here thererare many thousands of individual
`fittings nun every customer service drop is a
`potential‘%1nterference—antenna."
`It is the
`interference problem in the feeder portion of
`the cable system that makes using it for return
`video signals impractical. Return video signal
`service is possible in the trunk portion of the
`system, and data return signals are practical
`for the feeder portion of the system.
`An aural
`return signal service via cable would seem to
`be of limited value because of the existing
`service provided by the telephone company.
`This leaves the most practical design for the
`upstream portion of a two—way CATV system as
`video and high—speed data by trunk cable, and
`data only by the return feeder cable.
`
`The next.consideration is in the allocation
`of the limited bandwidth in the cable system to
`forward and return channels.
`It should be
`obvious that increases inlbandwidth allocated to
`the return signals causeudecreases in the band-
`-width available for forward-video signals.
`’Fortunately data signalslusully require consid-
`erably less bandwidth than do video signals, and
`data signals can be both time and frequency
`multiplexed, as well as "area" multiplexed which
`will be described later. Probably the best
`allocation would be approximately 250 MHz for
`forward service use channels, and only about 25
`Hz for the return service. More details about
`the basic two—way system in each stage of its
`evolution will be provided later.
`
`Applications of Two—Way CATV
`
`One of the greatest obstacles to the
`continued development of two—way CATV technology
`has been the attraction of necessary investment
`capital.
`Investors do not see sufficient return
`from any application of the current technology to
`justify the risk.
`The exploitation of two-way
`CATV app1ications.has failed because each
`application has been considered in isolation,
`without a conwergenn of multiple applications
`for cost-sharing the two-way plant. And, further
`the two-way technology has never evolved asva
`synthesis of practical need and cost—efficient
`technlogy. Two-way.has been considered in term
`of some end-state of both rechnnlogy«and‘agp1i-
`cation.
`The step—at—a-tim.mpproach‘has not been
`followed.
`
`Unlike other communication media, two-way
`CATV has captured the inerest of the public
`sector early in the developmental stages. what-
`ever the future of tuo~wmy canunication, there
`is almost no doubt that the ublic sector will
`play a prominent role,.and that to~way CATV will
`involve applications from both the public and
`private sectors.
`
`A wide variety of public sector applications
`for the two—way CATV technology have been
`
`developed through the National Science
`Foundation research.
`The MSU team has developed
`applications which include a program to diagnose
`developmental delays in children under age five
`in the home, a large scale cable information
`and referral servio based upon a series of
`interactive television vignettes describing
`various social services and programs within the
`community, providing an extension and supplement
`to elementary science education through
`teleconferencing and computer—aided instruction,
`and a series of legal communication applications
`including an automated legal library, publica-
`tion of court-generated information,
`the taking
`of depositions, and the use of the system as a
`research tool to evaluate the effect of
`television advertising on children. Other
`applications have been suggested by other
`research teams.
`
`Private sector applications of two-way CATV
`technology have lagged behind the public sector
`applications because of limited research and
`development money in the relative1y—small cable
`industry. Further,
`the industry has been
`preoccupied with more immediately—profitable
`commercial applications such as pay channels.
`The private sector application receiving the
`most attention is per—program pay TV, with the
`previously discussed Telecinema system the only
`large scale operational example. Beyond per-
`program pay TV,
`there are few demonstrations of
`any private sector applications of two-way
`technology.
`For the future, other private
`sector applications may include marketing and
`advertising research,
`in-home shopping, and
`in-home monitoring and surveillance services.
`Among the suggested marketing and advertising
`research applications are television audience
`measurement, television advertising copy pre-
`testing and post-testing, television program
`pilot testing, package design tests, advertising
`concept tests, product purchase behavior
`measurement, and various other questionnaire-
`oriented research including awareness and
`preference measurement. Among the in-home
`shopping applications are electronic supermarkets
`and catalogs using special dedicated channels
`and interactive advertising. Among the in-home
`monitoring and surveillance applications are
`monitoring heat and smoke detectors, intrusion
`alamms,
`tamper alarms, power load management and
`utility metering; and, metering applications
`involve the remote reading of utility meters
`with the capability of charging differential
`rates depending upon the time-of-day, and the
`ability to turn off various in-home applicances
`to reduce the load in the event of an emergency.
`Further in the future are other applications
`such as electronic mail delivery, electronic or
`automated newspapers, and the electronic public
`forum concept.
`
`While the list of suggested applications
`for two-way CATV can be greatly expanded beyond
`the general categories mentioned here, such
`lists almost always consider two-way CATV tech-
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`nology as a fully developed monolith. Rarely is
`two-way CATV technology considered as an
`evolutionary process, with some applications
`preceding others as the technology and demand
`develops.
`It should be obvious that some
`applications of two-way CATV, such as per-
`program pay TV, are possible given the state of
`the technology today, and other more complex
`applications such as power load management
`require continued technological development.
`
`In order to simplify the relationship
`between the technological evolution of two—way
`CATV and the applications, a classification
`scheme of six categories will be used.
`Ignoring
`all applications which primarily involve
`comunication in an institutional framework, such
`as high speed data communication between banks
`or upstream video transmission from city hall to
`the cable transmission center, and concentrating
`on applications involving communication with
`only digital return from homes,
`the classifi-
`cation scheme includes the four private sector
`applications already discussed—-pay entertain-
`ment, shopping services, marketing research,
`and monitoring services--plus categories in
`education and community information.
`The
`education category includes the in—service
`training applications in an in-home setting
`along with various adult education applications.
`The community information category includes the
`electronic~mail delivery application, automated
`newspapers and related services,
`the public
`forum concept, and the social service information
`and referral system.
`The next task is to
`consider the evolutionary steps in the develop-
`ment of two—way CATV technology.
`
`The First Generation
`
`The first generation in the proposed model
`for two—way CATV system development was designed
`for a per—program pay TV system in Columbus,
`Ohio, and represents the important first step in
`the evolutionary process of two—way CATV tech-
`nology.
`The Telecinema per—program pay TV
`system has been in operation for nearly four
`years.
`The Telecinema system involves a home
`terminal which costs approximately thirty
`dollars, and allows four channels of pay TV
`programming.
`The subscriber selects the
`appropriate channel, and is then billed only for
`the programs that are watched. This method of
`pay TV is contrasted with per channel pay TV
`where the subscriber pays a flat monthly fee
`for unlimited viewing.
`
`A typical pattern for per—channel pay TV
`system is very high initial growth, probably
`around forty percent, followed by a drop to
`around 25 percent after the first few months of
`operation. Part of the explanation for this
`"churn" is the fact that people use only a small
`portion of the entire package of programs that
`is available, but feel they are paying for all of
`it--a sense that they are overpaying in relation
`to their usage.
`
`The Telecinema per—program system was
`tried first by charging subscribers only for the
`movies that were watched. Penetration was eighty
`percent and average monthly revenues were about
`four dollars, which was not enough to cover the
`costs of both the movies and the two—way system.
`In 1974, a three dollar maintenance fee was
`added. This caused the penetration to drop from
`eighty percent to forty percent, but the
`subscribers who dropped the service were those
`who did not watch many movies. Revenue
`increased to eight dollars per month among the
`remaining forty percent penetration.
`
`In December of 1975 Telecinema began
`experimenting with other forms of programing
`in addition to the core of Hollywood films.
`Adult films, children's films, sports events,
`nightclub performances and foreign films have
`been added. Average revenue has now increased
`to eleven dollars per month, and with increased
`experience in programming and advertising
`Telecinema is now predicting average monthly
`revenues of fifteen dollars per month within
`the next two or three years.
`
`The implications for program producers are
`obvious, especially when related technology
`such as satellite program distribution is
`considered.
`The Telecinema system with over 5000
`subscribers, is now the only operating per-
`The
`program pay TV system in the United States.
`system was designed to solve the early technical
`problems found when attempting to use interroga-
`tion—response type terminals in CATV applica-
`tions——the high cost of the terminals and RF
`interference. Early cost estimates for in—home
`terminals ranged from $300 to $1,000, which is
`obviously too high to permit profitable
`operation.
`System maintenance costs, because
`of signal intrusion, were also estimated to be
`prohibitively high.
`
`In order for two—way CATV to become
`economically feasible, it was necessary to
`design a system around a reliable terminal that
`would cost approximately $50, and be part of a
`system that can be reasonably maintained.
`The
`solution was suggested after consideration of
`the types of multiplexing available for the
`return data signal generated by the in—home
`terminals.
`Time division multiplexing (TDM)
`offers the advantage of sharing a single
`frequency for all the terminals, but can easily
`be jammed by one malfunctioning terminal.
`The
`source of the trouble is very difficult to find.
`Frequency division multiplexing (FDM) solves the
`problem of terminal jaming, but if very many
`terminals are to be used,
`too much spectrum
`space is consumed.
`The solution is a
`combination FDM/TDM system which allows the
`"area" multiplexing.
`It consists of the
`simultaneous transmission of groups of 100
`frequency multiplexed terminals at different
`time intervals.
`
`54
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`IEEE TRANSACTIONS ON CABLE TELEVISION, JANUARY 1977
`
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`
`Area multiplexing is accomplished through
`the use of digitally controlled code operated
`switches (COS).
`Each COS consists of band-
`splitting filters which separate the downstream
`(50 to 300 MHz) frequencies from the upstream
`(5 to 30 M2) frequencies. Downstream signals
`pass through the COS continuously without
`interruption, while the upstream frequencies are
`either passed or blocked as directed by a digital
`signal generated by minicomputer. This now
`allows an entire system of in—home terminals to
`be scanned in groups of 100 by activating and
`deactivating appropriate COSs. Placing a primary
`COS at each trunk, and a secondary COS at each
`bridger amplifier makes possible the scan of an
`entire feeder branch which would normally consist
`of between 100 and 200 homes. This design can
`be seen in figure 1.
`
`The use of the COS system allows for a much
`less expensive terminal than a typical interro-
`gation—response terminal because a great deal of
`circuity can be eliminated,
`including the RF
`receiver, decoder and address—recognition
`circuitry.
`A simple FDM terminal requires only
`a data encoder and RF transmitter circuity,
`which with the area multiplexing affected by the
`COS network is all that is required.
`The home
`terminal consists of a modified CATV converter
`which costs approximately $40.
`The modification
`consists of the addition of a circuitry board
`containing only an FSK transmitter and data
`encoding circuitry, Costing
`an additional $20.
`The terminal transmitter is assigned a discrete
`frequency in its own COS area, and is transmit-
`ting all of the time. Each terminal transmits
`a 16-bit data word which indicates the status
`of the converter including the channel selected,
`whether the subscriber's television set is off
`or on, and whether the security key on the
`converter is on or off.
`
`A General Automation SPC 16 minicomputer
`manages the entire scanning operation through
`the use of special interfaces which control a
`COS addresser and RF receiver.
`The minicomputer
`operating in real time, routinely scans the
`system collecting data and generates viewing
`reports. Additional routines are available for
`terminal installation and system maintenance.
`Batch programs generate billing and other reports
`required by the cable operator.
`
`'
`
`System maintenance is easily accomplished
`through the combined use of the minicomputer
`and the COS network to isolate interference and
`other problems.
`End of line oscillators (ELO)
`at the end of each feeder line, add a unique
`carrier frequency for easy identification and
`help in balancing the system.
`The Columbus
`system is maintained in this manner using one
`technician for the approximately 200 miles of
`plant.
`
`The first generation two—way CATV system is
`primarily designed as a per program entertainment
`system.
`It does not allow for any interactive
`
`response, but only relatively simple monitoring
`of the status of the CATV converter attached to
`the television set.
`The only other feasible
`application for first generation technology is
`simple television audience measurement, since
`the system can be scanned at more frequent
`intervals than commercially available mechanical
`diary services.
`The first generation, however,
`has clearly demonstrated both the technical and
`commercial viability of this technology, and
`paves the way for new generations.
`
`The Second Generation
`
`The second generation system is designed
`for the MSU experiments being conducted in
`Rockford, Illinois with National Science
`Foundation funding.
`The National Science
`Foundation awarded seven planning grants in 1974
`designed to develop the potential of two-way
`CATV emphasizing applications in the public
`sector.
`In 1975 NSF funded research based on
`designs developed by three of the original
`grantees:
`the Alternate Media Center at New
`York University, Rand Corporation, and
`Michigan State University (MU).
`
`The MSU team is conducting an experiment
`using two—way CATV in Rockford, Illinois.
`The
`initial application involves the in—service
`training of firefighters, with an additional
`application in association with the University
`of Michigan involving the in—service training
`of elementary and secondary school teachers.
`The experiments represent a substantial
`investment of federal funds, with the MSU,
`University of Michigan projects costing over
`three—quarters of a million alone.
`The entire
`NSF investment is nearly three million dollars.
`
`Approximately one—third of the MSU project
`investment has involved the development of the
`necessary two—way CATV hardware and software
`required for the project. Additional investment
`has been made by Rockford Cablevision in
`constructing the necessary two—way plant in the
`city.
`The two-way CATV facility in Rockford,
`along with the nationally projectable socio-
`economic and demographic mix of households
`available in the community, make Rockford a
`natural experimental site for experiments in
`two-way CATV.
`
`The major difference between the first
`generation (Columbus) and the second generation
`(Rockford)
`is the addition of an interactive
`response capability at the terminal. Rather
`than providing only monitoring capability of the
`status of a channel converter,
`the channel
`converter selection buttons can be depressed to
`transmit a return signal. This requires
`relatively minor modification of the first
`generation terminal,
`including addition of
`interactive channels and a transmit button.
`additional channels allow the terminal to
`function as a converter as well as an interactive
`terminal.
`The transmit button, along with a
`
`The
`
`BLOCK AND WRIGHT: EVOLUTIONARY APPROACH TO CABLE COMMUNICATION
`
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`first Generation: Area Multiplexing
`
`cos AREA
`
`100 HOMES
`
`<1
`
`TRUNK AMP
`
`{ FEEDER AMP
`
`« TRUNK AMP WITH
`BRIDGER AMP
`
`———— TRUNK 0.750-IN. CABLE
`
`FEEDER 0. 500-1». CABLE
`
`i PRIMARY cos
`
`seconnanv cos
`
`C9
`
`END"0F"L I NE
`OSCILLATOR
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`insure the subscriber
`timed LED display,
`responding only when desired and at intervals
`longer than the minimum scan.
`The second
`generation terminal requires a push—button type
`converter, which is not necessary in the first
`generation.
`
`The transportation system of the COS net-
`work and ELOs remains the same as before.
`The
`major difference in the second generation is in
`the minicomputer system. Since more processing
`is necessary with the possibility of a response
`in addition to the monitoring already required,
`the minicomputer system needs to be augmented
`with extended core memory and sufficient disk
`storage to accomodate interaction.
`The primary
`advance to the second generation is not hardware,
`but rather computer software.
`
`The minicomputer software necessary to
`support second generation must not only perform
`the basic system scan routine and system main-
`tenance, but it must also process any response
`data in real time.
`The MBU team has developed
`a specialized minicomputer language designed to
`coordinate downstream video signals with the
`appropriate interactive response making it
`relatively easy for a non-computer oriented
`individual to make use of the two—way system.
`The specialized minicomputer language was
`designed for the in—setvice training projects in
`Rockford, but could be modified for other
`applications.
`
`The coordination of downstream video signals
`and the interactive response signals imply
`control of headend video equipment by the
`minicomputer system. This is accomplished by
`using computer-controllable character generation
`equipment, standard SMPTE time code interfacing
`with any video tape equipment, and standard
`process control input/output signals and relays
`to control the necessary video equipment. This
`makes possible minicomputer control of the entire
`two-way system.
`The second generation system is
`shown in figure 2.
`
`The second generation terminal costs more
`than the first generation because of the need
`for a more sophisticated basic converter, and a
`small amount of additional circuitry and terminal
`modification. Depending on the quantity, second
`generition terminal costs range from $100 to
`$150.
`
`The second generation interactive response
`capability opens many new application areas for
`two-way CATV technology.
`In addition to the in-
`service training applications described above,
`which this generation was designed to support,
`many applications are of interest to both public
`and private sectors. Applications of primary
`interest in the public sector include the public
`forum and the social service information and
`referral system.
`The second generation allows
`for upstream transmission of digital signals, but
`it does not allow the subscriber to receive
`
`individualized information, that is downstream
`informatio-must be shared when transmitted on
`the same channels
`"It is not practical to allow
`subscribers to have the downstream portion of
`any interactive programing "on-demand," rather
`such programming would be distributed on a pre-
`arranged schedule. This is an important limita-
`of the second generation technology.
`
`Private sector applications include in—home
`shopping services such as interactive adver-
`tising and a crude form of electronic catalog
`that would be operating on a fixed schedule.
`Marketing research applications can be greatly
`expanded because of the addition of active
`response. Multiple choice questions can be
`asked and special video material shown to
`respondents in their own homes.
`
`The capital cost of the first generation
`of two—way service is accommodated nicely by
`the per-program pay TV revenue.
`The incremental
`cost of the second generation, e.g., a more
`sophisticated terminal and greater computer
`capacity may be in the range of $20 to $30 per
`household or drop. Educational programs (public
`schools, public safety) which lease the service
`on a regular basis will cover a portion of that
`cost. Market research, direct selling and
`alarm systems should cover the remainder.2 Thus
`far we have achieved or projected achievement of
`a substantial portion of the "blue sky" of the
`early 1970s. However, monitoring applications
`in the second generation must be limited to
`simple closure switches, such as-a relay signal
`from a smoke or heat detector because only a
`few data bits are available in the terminal.
`
`Partially because of the limitation of
`second generation equipment in monitoring
`applications,
`the third generation is being
`developed“
`The imediate advantage of third
`generation two—way CATV technology is the
`ability to monitor activity in the home
`reguiring more complex code than a single bit.
`
`the cost
`1Without the channel converter,
`of the unit would be reduced by approximately
`$75.
`The stripped—down terminal device would
`provide only interactive response generated from
`a simplified push—button pad, perhaps only four
`buttons, but would not provide any monitoring of
`channel converter status. This would limit
`application of the system to interactive
`response, making per-program entertainment
`difficult.
`
`2The huge advantage of smoke detectors
`which communicate directly to the fire depart-
`ment should be noted. when the household is
`occupied,
`the simple alarm can save lives and
`property, but the property is protected only
`during occupancy. With a communicator linkage
`to the fire service,
`the property is protected
`at all times.
`
`BLOCK AND WRIGHT: EVOLUTIONARY APPROACH TO CABLE COMMUNICATION
`
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`58
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`IEEE TRANSACI'IONS ON CABLE TELEVISION, JANUARY 1977
`
`7
`
`
`
`
`
`
`

`
`The Third Generation
`
`A necessary part of any two-way CATV power
`load management system is the ability to monitor
`utility meters. While transmitting utility meter
`information through the upstream communication
`system represents no technical problem, assuming
`the 16-bit data format,
`the scan must be designed
`to prevent the reading of utility meters from
`occupying the entire system.
`The problem for
`terminal design is to provide 16-bit data words
`recognizable by the minicomputer as either
`utility meter information, interactive response,
`or channel status.
`The terminal itself would be
`required to swap channel status and utility meter
`information to make possible simultaneous per-
`program pay TV and power load management applica-
`tions.
`
`The only practical solution to the data
`formatting problem is the addition of'a micropro-
`cessor chip to the terminal. Microprocessors,
`such as the RCA 1800 COSMAC series, would add
`approximately $20 to the cost of the second
`generation terminal. Adding a ROM to store
`program instructions would allow microprocessor
`to accumulate utility meter data and fbrmat the
`16-bit transmission word at the appropriate
`times.
`The third generation terminal is cur-
`rently being developed.
`A working diagram is
`shown in figure 3.
`
`The addition of the microprocessor to the
`terminal provides flexibility to most second
`generation applications.
`The ability to format
`the 16-bit transmission word within the terminal
`makes possible more complex data to be transmit-
`ted from the terminal than simple multiple choice
`selections.
`In the in-home shopping application,
`more complex information such as color, size or
`credit card numbers could be quickly entered
`through the keyboard, and then transmitted all at
`once rather than digit by digit.
`The marketing
`research and educational applications would also
`benefit from the increased input flexibility by
`being able to accept input data more complex than
`a single digit.
`
`Another improvement is terminal technology
`is necessary at this step before moving ahead to
`the fourth generation.
`To improve control and
`security of the system, it is desirable
`to move
`the essential electronics out of the TV control
`terminal to a central location. This shift,
`the
`third-and-a-half generation, does not add any-
`thing in terms of potential applications, but
`rather provides more efficient operation because
`of increased maintenance convenience and terminal
`security.
`The latter is of critical importance,
`particularly in the utility metering applications,
`where thefts of service of staggering magnitude
`have recently been discovered.
`
`The Fourth Generation and Beyond
`
`The evolutionary steps beyond the third
`generation are not as clear as the first steps
`because the associated electronics and informa-
`
`tion processing technology itself are continu-
`ally evolving.
`The next step will no doubt be
`the addition of low cost memory storage in
`either the terminal itself, or in a COS. This
`will make possible the transmission of time-
`compressed digital signals to a memory in a
`specific location such as an individual termi-
`nal.
`
`The addition of the microprocessor chip to
`the terminal also makes possible the decoding of
`downstream information with the addition of a RF
`receiver to the terminal. While additional
`signal decoding and character generation cir-
`cuitry would also be required, it is technically
`possible to allow selection of portions of down-
`stream data signals using keying or-addressing
`scheme.
`If an entire downstream channel were
`devoted to digital information then it would be
`possible to "page" a portion of that data stream
`for local display on the home television set.
`This makes possible electronic automated news-
`papers which the subscriber can page through on
`demand. One video channel could easily accomo-
`date the equivalent of 1,000 pages.
`The news
`could be computer refreshed and controlled.
`Another application is the delivery of second
`class mail and on demand catalogs. The limita-
`tion are restriction to digital information.
`The information is always stored in the down-
`stream communications channel, which given the
`limited available bandwidth, may not be the most
`efficient use of the spectrum.
`
`The addition of memory partially solves
`the problem of inefficient use of available
`spectrum space, since the electronic newspaper
`or mail would not always be present in the
`system, but rather multiplexed on a downstream
`channel carrying similar signals to other termi-
`nals. Not only does this provide for better
`spectrum use, but also allows the transportation
`of more personalized messages.
`
`For this generation of two-way CATV termi-
`nal to becoe feasible,
`the cost of memory will
`have to drop substantially, which should result
`from improved memory technology such as the de-
`velopment of the "bubble memory." This genera-
`tion also implies substantial increases in the
`amount of computer power necessary to run the
`system. with each new generation,
`th