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Technology of Cable Television.Cable Television Information Center, Washington,D.C.Ford Foundation, New York, N.Y.; John and Mary R.Markle Foundation, New York, N.Y.7333p.Cable Television Information Center, The UrbanInstitute, 2100 M Street, N.W., Washington, D.C.20037

EDRS PRICE MF-$0.65 HC Not Available from EDRS.DESCRIPTORS *Cable Television; *Community Antennas; Community

Change; Community Leaders; *Community Planning;Community Programs; *Decision Making; Local Issues;Social Change; *Technological Advancement;Telecommunication; Television

ABSTRACTThe technology of cable television (CATV) is one area

in which local community officials need to develop knowledge so thattheir decisions about the structure of CATV within the community willbe informed. Thus, this paper is designed to familiarize localdecision makers with the technological aspects of cablecommunications, to isolate specific questions which local officialsmust consider as they plan for CATV in their communities, and to noteand explain options available to franchising authorities in dealingwith those questions. Section One of the report describes cabletechnology past, present and future; the second section considersissues involved in systems design technical performance standard, andthe implementation of future technology. (Author/SR)

5

Cable TelevisionInformation Centerthe urban institute

Technology of Cable Television

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Copyright © 1973 by Cable Television Informa-tion Center, The Urban Institute. All rights reserved.No part of this document may be used or reproducedin any manner whatsoever without written permissionexcept in the case of brief quotations embodied incritical articles and reviews. For information address:Cable Television Information Center, 2100 M Street,N.W., Washington, D.C. 20037. Att: InformationGroup.

TECHNOLOGY OF CABLE TELEVISION

U.S. DEPARTMENT OF HEALTH,EDUCATION & WELFARENATIONAL INSTITUTE OF

EDUCATIONTHIS DOCUMENT HAS BEEN REPRODUCED EXACTLY AS RECEIVED FROMTHE PERSON OR ORGANIZATION ORIGIN.ATING IT. POINTS OF VIEW OR OPINIONSSTATED DO NOT NECESSARILY REPRESENT OFFICIAL NATIONAL INSTITUTE OFEDUCATION POSITION OR POLICY.

CABLE TELEVISION INFORMATION CENTERThe Urban Institute

2100 M Street, N.W., Washington, D.C. 20037

PREFACE

This document was prepared by the Cable Television Information Center under grantsfrom the Ford Foundation and the John and Mary R. Markle Foundation to The UrbanInstitute.

The primary function of the center's publications program is to provide policy makersin local and state governments with the information and analytical tools required toarrive at optimum policies and procedures for the development -of cable televisionin the public interest.

ACKNOWLEDGMENTS

The center is indebted to The MITRE Corporation, McLean, Virginia.

CONTENTS

INTRODUCTION 7

I. TECHNOLOGY OF CABLE TELEVISION 7

A. Traditional CATV Systems 7

B. Modern Cable Television I 11

C. Broadband Communications Cable's Future 14

II. MAJOR ISSUES FOR FRANCHISING AUTHORITIES 19

A. Design Decisions 19

B. Technical Standards 29

C. Role in the Evolution of Cable Technology 32

III. CONCLUSION 33

INTRODUCTION

Cable television's entrance into a communityposes special problems for local officials.Although it is an opportunity to determine howthe community wants to regulate a new service

a new medium of communication it is anopportunity often overlooked. Taking full advan-tage of the opportunity usually requires a basiceducational effort so that decisions can be madeon the basis of a working knowledge of how cabletelevision operates, how local citizens can makeuse of it, and what decisions local authorities cantake responsibility for making.

The technology of cable television is one areain which local officials need to develop the know-ledge on which to base their decisions. It is impor-tant that local decision makers understalnd cabletelevision technology for several reasons. First,because a cable television system's technicaldesign importantly influences its social and enter-tainment usefulness, systems should be plannedwith thorough consideration of local demog-raphic, social, and political characteristics and theservice demands which these characteristics maymake on that system. Second, since there mustbe reliable delivery of high quality television sign-als if cable is to perform adequately any of itsexisting or projected functions, franchisingauthorities should establish technical standardsagainst which the performance Of a system canbe measured. Third, because cable technologywill continue to grow in sophistication, local offi-cials will want to develop regulations that will per-mit their community to accommodate changes inthat technology.

This publication has three goals:

To familiarize local decision makers with thetechnological aspects of cable communications;

To isolate specific questions which local offi-cials must consideras theyplan for cable televisionin their communities; and .

To note and explain, where applicable, optionsavailable to franchising authorities in dealing withthose questions.

Section 1 of this report describes cabletechnologythe first goal of this paper. The basiccomponents of a cable television system areexplained both in the historical context of howmost systems were built before governments andcitizens were aware of cable's potential impor-tance, and how systems are being planned today.Discussion is also directed to the role of cablecommunications in the future.

7

The second and third goals are treated in SectionII. The issues involved in system design, technicalperformance standards, and the implementationof future technology are examined from the per-spective of the local public official faced with deci-sions.

TECHNOLOGY OFCABLE TELEVISION

This chapter explains how traditional commun-ity antenna TV (CATV) systems work, discussesthe technical characteristics of modern cable tele-vision, and, examines problems and prospects forbroadband cable .communications -4-- theadvanced systems that exist now only in pro-totype.

A. Traditional CATV Systems

Cable television began by providing a servicewhich extended the range of broadcast televisionstations, or, differently put, brought broadcast TVto those who could not otherwise receive it.Broadcast television service is most attractiveeconomically when the area it covers (a radiusof roughly 35 miles around the transmitter) is heav-ily populated. The reason is that broadcast televi-sion station revenur ;s derived almost entirelyfrom advertisers, ,,t:hu pay for "time" on anamount-per-viewer basis. The more viewers a TVstation reaches, the more it can charge for audi-ence time.

However, the ability to saturate an area, whileimplortantitO the station owner and advertiser,poses certain disadvantages. Once a television sta-tion begins to broadcast, the same assigned fre-quency, or channel number, cannot be used byany other broadcaster within 200 miles; the twosignals will interfere with one another.

Further, a local station broadcasting on a VHF(broadcast channels 2-13) channel adjacent to thechannel of another station within 100 miles willinterfere with the distant signal. The 12 VHF chan-nels are not all adjacent to one another. But inter-ference problems among those that are, limit thenumber of VHF broadcast television stations aviewer can receive to seven.' Table 1 illustratesthis problem in Baltimore and Washington.

In practice, the economics of broadcast televi-sion usually, limit the number of stations evenfurther. Small cities and towns simply do not have

'Any of two TV channels are considered adjacent when theirvideo carriers are 6 MHz apart. Channels 4-5 and 6-7 are theonly non-adjacent channels.

8

enough viewers to support more than one or twostations. It is this economic limit which hasretarded the development of UHF televisiononce thought to be the key to diversity and local-ism in television service because of the numberof channels.

CATV systems grew in towns whose citizensreceived either poor reception or no signals atall. These systems typically provided one to fivebroadcast TV signals to subscribers, and thus werenot radically different from broadcast televisionservice.

However, cable TV systems do use coaxial cableas a medium for delivering television signals, withcharacteristics different from broadcast TV. Asingle cable can carry as ,many as 40 televisionsignals that do not interfere with each other fromone point to another. Further, because signals car-ried by cable'Veak" only slightly from the insideof the cable, q.re frequencies used in one cablecan be used again in another cable next to it.

Hence, the number of stations that can be carriedis limited by the number of cables one can affordto lay not by any fundamental restvictions asin broadcasting.

Finally, since the cable protects signals it carriesfrom ocAside interference, it potentially canderiver i1 !1;;,ter quality signals than those receivedoff-thcx.

A CA,TV system consists of three components:A headend, or control centerA distribution system a network of cables

which delivEr signals to subscribers' homesA subscriber terminal in this case, merely

the subscriber's television set.

HEADEND

The headend includes an electronic controlcenter (sec.. Figure 1), which may or may not behoused near e 100 to 500 foot tower with a sensitiveantenna mouir:ed on it for each broadcast televi-

Table 1. TV Channel Allocations (VHF)

CHANNEL

2

3

BALTIMORE

WMAR-TV

WASHINGTON OTHER

Harrisonburg, Va.

4 WRC-TV

and Philadelphia, Pa.

Richmond, Va. and

5 WTTG

6

7 WMAL-TV

Philadelphia, Pa.

Richmond, Va. and

9 s WTOP-TV

Lancaster, Pa.

Altoona and Phila-10

11_..WBAL-TV

12

delphia, Pa.

Richmond, Va.,), Wilmington, Del. and

Lynchburg, Va.

But separate cable systems in Baltimore and Washington could each carry a full twelve channels (2 through 13)without the possibility of major interference.

Source: Charles Tate, ed., Cable Television In the Cities: ComniUnity Control, Public Access and Minority Ownership (Washington: TheUrban Institute, 1971), p. 9.

,-!

aFigure 1. Control Center for a Cable Television System Headend.

sion signal received by the system (see Figure 2).The antenna is sited to provide the best availablesignal reception. Each received television signalpasses through a processing amplifier, whichseparates the sound and picture components, andadjusts the signal levels to prevent a strong signalfrom one channel from overpowering another onan adjacent channel (as often happens in broad-cast television): Thus, all 12 VHF channels can beused. The amplifier then reassembles the pictureand sound signals for transmission th roughout thedistribution system.

UHF signals are broadcast at levels above therange of frequencies which can be transmittedvia cable electronics. In a cable system which alsocarries UHF television signals, the headendincludes electronic equipment to convertUHF sig-nals to unused VHF channel frequencies withinthe cable system spectrum.

Figure 2. Antennas and Tower for a Cable Television SystemHeadend.

9

DISTRIBUTION SYSTEM

The process of transporting signals trom theheadend to the subscriber is commonly referredto as "downstream" communication; the tradi-tional cable system,is capable of communicationin the downstream direction only. The distributionsystem for one-way communication consists of acoaxial cable and the electronics necessary totransport signals from the headend to the sub-scriber. The basic element is a coaxial cable; thecable consists of an inner conductor, generallymade of copper or copper-clad aluminum sur-rounded by an insulator (such as extruded foampolystyrene or extruded foam polyethylene)which is in turn enclosed by an outer conductor,typically aluminum (see Figure 3). Coaxial cablesused by the cable television industry range indiameter from one-quarter to one inch.

plastic sheathing

\1outer conductor

plasm foim

inner conductor

Figure 3. Coaxial Cable.

The distribution network, or "plant," is dividedinto two portions, trunk lines and feeder lines.Trunk lines, which are constructed of one-half tothree-quarter inch coaxial cable, are the majorarteries of the cable system. They transport thesignals from the headend to the extremities ofthe cable system. Feeder lines, which are con-nected to the trunk lines, carry signals past eachhome. In a typical distribution plant, there is twoto five times as much feeder cable as trunk cable.Although individual trunk lines are longer thanfeeder lines, there are a far greater number offeeder lines.

Both the trunk line and feeder lines employ elec-tronic amplifiers which are installed at specificintervals to boost the cable signal, as shown inFigure 4. Feeder lines are connected to the trunklines by an electronic device called a bridgeramplifier. This amplifier draws signal power from

10

Figure 4. Cable and Amplifier.

the trunk for further distribution, and protects thetrunk lines from electronic disturbance in thefeeder lines.

Subscribers' television sets are connected to thefeeder lines with. a subscriber "drop" line. Thesubscriber drop consists of a tap at the feeder,the drop cable (typically one-quarter inch diame-ter cable), and a room wall plate connector. Ashort length of coaxial cable runs from the wallplate and is connected to the antenna terminalsof the television set via a matching transformer.

An understanding of the electronics in the dis-tribution system is helpful in making decisionsabout system layout and capacity.

Two problems in the electronic operation ofcable system distribution limit the size of the geog-raphical area a single cable system can serve. Theyare termed attenuation and distortion.

Coaxial cable attenuates, or weakens, a signalit carries. As a television signal, flows throughcable, the signal strength, or power of the televi-sion signal, diminishes; a typical coaxial cabletrunk line has its signal reduced to 1/100 of itsoriginal strength for approximately every 2,000feet of cable. The reduction of signal strengthbecomes perceptible to the viewer as a 'snowypicture. To counteract this attenuation, amplifiersare connected to the coaxial cable to boost signalstrength.

Unfortunately, the amplifiers themselvescause the second problem distortion. Both

cable and amplifiers introduce random electronicimpulses into the television signal as it travelsthrough the distribution system. These impulsesare called "noise," and appear on the televisionscreen as snow. Since each amplifier boosts boththe signal and the noise, there is a limit to thetotal number of amplifiers which can be attachedto a length of cable. Current design permits signalsto be processed by 18 to 25 trunk amplifiers ina row ("cascade") before the amount of snowbecomes objectionable.

The distance between amplifiers depends uponthe degree to which each amplifier boosts thesignal. The amount of boost is limited becauseat high signal output, the amplifier produces otherkinds of signal degradation. These degradations,called intermodulation and cross-modulation dis-tortion, appear on the television set as movingbars or stripes.

Trunk cable amplifiers are operated at lowpower levels to minimize amplifier-produceddegradation. In practice, the distance betweentrunk amplifiers is about 2,000 feel. Thus, in com-bination, the amplifier cascade limit and the max-imum distance between amplifiers defines themaximum distance for trunk cable to be 7 to 10miles.

Feeder cable amplifiers (sometimes called lineextenders) feed signals to the subscriber. Theyare operated at higher power levels than trunkamplifiers in order to permit more subscribers tobe fed from a single amplifier. Since the feederamplifiers are operated at higher power levels thanthe trunk amplifiers, the number of cascadedfeeder amplifiers is normally limited by (1:stortionconsiderations to three. The distance betweenfeeder amplifiers is less than between trunkamplifiers, because the large number of sub-scribers drain signal from the feeder cable. In prac-

i» III)) I4'4

Figure 5. Cable Distribution Network for a Cable TelevisionSystem.

lice, feeder cable extends no more than 4,000 feetfrom the trunk, and often less. Figure 5 illustratea typical trunk and feeder network.

SUBSCRIBER TERMINAL

"Subscriber terminal" is a term more approp-riate to the description of advanced rather thancontemporary systems. Here, in the case of tradi-tional CATV systems, the term refers simply tothe subscriber's television receiver; in an ad-vanced cable system it would consist of a televi-sion receiver in addition to other facilities, andwould he capable of two-way communication andother services.

The standard television receiver is capable ofreceiving two bands of television broadcast fre-quencies: VHF and UHF. Unfortunately, as Figure6 illustrates, present cable electronics design fre-quencies are not broad enough to encompass UHFtelevision frequencies. System operators deal withthis problem partially, by converting UHF signalsat the headend to unused VHF channels. But whilethe operators can deliver as many as 35 channelsto subscribers' homes, the standard television -receiver can receive no more than 12 of thosechannels.'

The standard receiver is equipped with elec-tronic circuits that enable it to tune and receivebroadcast signals. These circuits are not necessaryfor cable reception and may introduce unwantedbroadcast signals that will interfere with cable,sys-terns. This problem can be reduced if the cableoperator is permitted to modify the-Inside of thetelevision receiver or connect the cable directlyto the tuner.

A more practical solution is the developmentof a special cable receiver, designed to receiveall 35 channels from the cable. Research anddevelopment is taking place, but as yet there isno such cable receiveron the market. In the mean-time, other arrangements have been devised toincrease capacity. These arrangements will be dis-cussed later in more detail.

B. Modern Cable Television

Traditional cable television was developed toprovide television service to communities too

'Although cable electronics permit transmission of 40 televi-sion channels simultaneously, at present no manufacturer hasdesigned a system that delivers more than 35 channels to sub-scriber's': Thus, although the electronic capacity of cable is40 ch;?,nnels, subicriber service for the time being will probahlybe `iunited to 35 channels.

UHF tekvision(channels 14 to 70) <

Aeronautical and mobile.<communications

VHF television(channels 7 to 13)

Aeronautical and mobilecommunications

FM radioVHF television(channels 2 to 6)

Mobile communications

-S06

)16

174

10888

54

30

3

MHz

600

500

400

II

III

II

1101111111

300

200

100

Approxin ate rangeof fret uencies

on cable

Figure 6. Television Frequency Spectrum

small to support a television station, or too farfrom cities that did have stations. Traditional CATVwas essentially a retransmission service; but asthe cable industry flourished, traditional systemsprovided the economic base for the furtherdevelopment of cable television technology.

Traditional cable television systems developedin areas where broadcast television is poor. Today,systems are built in areas where broadcast televi-sion service is available. Consequently, the pro-vision of standard television signals will not beenough, and cable operators in urban environ-ments will have to provide new and more diverseservices. The result will be a more technically com-plex cable system.

1. Headends are becoming more sophisticated,with the addition of new features:

Electronic importation of distant television sta-tions

12

Live studio programming exclusively for thecable system

Automated programming of news and weatherMultiple headend interconnection for large

systems.2. Distribution systems are beginning to havemore capacity as many as 35 channels deliveredto subscribers.3. Subscriber terminals will include devices thatbypass weakne,ses of the teleion receiver.

HEADEND

As in the traditional cable system, the headendin a modern system includes the antennae, andthe electronic control center for amplifying broad-cast signals received and converting UHF signalsto VHF frequencies before transmitting themthrough the distribution system. Additionalfacilities are now required to produce the newservices.

Electronic Importation ofDistant Television Signals

Cable systems are required to carry certain tele-vision stations which place a signal over the sys-tem's service area. Cable operators offer addi-tional program services by importing televisionsignals from distant markets. Since the signals arereceived near the distant market and transportedto the local headend by microwave radio systems,one additional feature of a modern headend isthe equipment necessary to receive and modulatemicrowave signals.

Microwave transmission is a system of broad-casting from one point to another 20 to 35 milesdistant. To import a television station, a transmit-ter near the station radiates the signal in a specificdirection toward the distant receiver ratherthan uniformly in all directions as is done withradio and television broadcasting. Microwave sta-tions must be cascaded when stations from greatdistances are imported. For example, importinga television station from a market 200 miles awaymight require "hops" between three to five mic-rowave stations. Microwave service may be pro-vided by the telephone company, or byspecialized common carriers, or it may be ownedby the cable system operator himself.

Live Studio Programming

System operators frequently operate !ocalstudios to program a channel. The Federal Com-

munications Commission now reouires that allsystems with more than 3,500 subscribers mustoperate to a significant extent as a local outletby origination cablecasting.'

Studio facilities for cablecasting vary in cost,ranging from as low as several thousand dollarsfor facilities bUilt around a half-inch black andwhite video tape recorder, to a full color profes-sional studio that may cost S1 million or more.

Automated Programming

Many system headends now include automatedorigination providing specialized services otherthan conventional telecasts. Automated equip-ment packages provide time, weather, stock tickerand news (AP or UP) wire services, many withalphanumeric message capability. At least onemanufacturer markets a computer controlled vid-eocassette player, which permits the systemoperator to play pre-recorded three fourth inchvideotapes automatically.

Multiple Headend Interconnection

Headends are now becoming increasingly com-plex because of the need for interconnection of.systems. Interconnection is necessary when acommunit-, st: large that it must be served byseveral headends and distribution systems (called"hubs"): It may also develop when several con-tiguous cable systems in neighboring com-munities interconnect to share local program-ming.

Interconnection can be achieved by cable (in-cluding a new one inch cable with low signal losscharacteristics, called "supertrunk"), or by mic-rowave. This microwave is not the one-point-to-another kind used to import distant televisionsignals, but a new service called Local DistributionService (LDS). These microwave systems have thecapability of transporting a large number of televi-sion pictures (from 8 to 38) from one site to anumber of receiving locations, without visibledeu.Idation of signals (see Figure 7). Supertrunkis usually favored over LDS where weather condi-tions do not allow reliable LDS operation or wheretwo-way capability is required, such as in a systemwith a number of local origination studios thatneed to be interconnected. However, in urban

'In United States v. Midwest Video Corp., 406 U.S. 649 (1972),the Supreme Court upheld the FCC's authority to impose theorigination requirement. In the course of that litigation, how-ever, the commission stayed the effect of the rule. Upon affir-mation by the Supreme Court, the commission did not moveto vacate the stay. There is some question, though, whethersuch action was necessary and the commission has not statedwhether the rule is in effect.

f",

environments where underground construction isnecessary, microwave may be the least expensiveone-way interconnection system. In some circum-stances, a combination microwave and cable sys-tem for two-way interconnection may be lessexpensive than an all-cable system.

If interconnection of cable systems is desired(either presently or in the future), the technicalstandards for the distrih, n system must bemore strict than those for .ind alone" system.Whether microwave or caith., is used to intercon-nect hubs, some additional distortions bothmore noise (snow) and more in termodulation aridcross-modulation (moving bars) will occur. Asa result, to obtain the same quality signals as thosecarried by a single hub system, the number oftrunk and feeder amplifiers cascaded in a multiplehub system must be smaller.

Traditional systems use a one-way "tree" layoutthat can be likened to a party line that is, allsubscribers share the same facilities and receivethe same programming (see Figure 8). A "fullyswitched" system such as the nationwide tele-phone network permits two-way private line com-munications by connecting each subscriberdirectly to a vast network of switching centers andalternate signal routes (see Figure 9). Intercon-nection, if properly designed, helps offset theparty line character of cable system.

Interconnection permits headends to act asswitching centers. Interconnection switchingfacilities allow one hub to receive programs ofparticular interest to its subscribers, while anotherhub does not. Or, switching facilities within a hubmay also permit subscribers connected to aspecifi, trunk to receive special programming (forexample, a locally cablecast high school baseballgame) while other trunks do not. Such limitedswitching capabilities are not nearly as sophis-ticated as the fully switched telephone system,but they do increase the flexibility of downstreamone-way service and in the future may increasethe efficiency of two-way services.

Although switched cable systems exist, they areriot widespread in the United States. Switchingcenters are costly, and urban communities wouldrequire a large number of centers. Furthermore,the cost of laying the large number of cablesrequired might be prohibitive, especially if thecables were placed underground.

DISTRIBUTION SYSTEM

The modern distribution system consists of thesame elements as the traditional one coaxialcable, amplifiers, and so on. However, with the

13

Figure 7. Microwave Interconnection of C.:ble Television Sys-tems.

Figure 8. Cable Television Systems Use a Tree-Shaped Network.

Figure 9. Telephone Systems Use a Switched Network.

14

increase in the number of services provided,several problems arise. As mentioned earkr, astandard television receiver is capable of receivingonly 12 of the35 channels cable can carry. Further,a strong local broadcast signal will interfere witha cable signal carried on the same channel whenthe two signals meet in the television receiver,making that channel unusable. Thus, distributionsystems have to be modified to overcome theselimitations.

Two approaches have been developed to solvethese problems. The first, and generally the mostexpensive, is to bring additional cables to eachhome and provide a switch allowing the subscriberto switch from cable to cable, receiving up to 12channels on each one. This approach uses only12 of the 35 channels in each distribution cable

but it does provide a means of receiving morethan the 12 channels on the television set. Further,this approach led the cable industry to developprototype advanced two-way systems based onthe presumption of a dual cable distributionsystem.

The second approach does not involve the dis-tribution system, but rather the subscriber ter-minal.

SUBSCRIBER TERMINAL

More recently, system operators have increasedcapacity by installing a converter instead of extracables. Depending on the model, the converterpermits the subscriber to tune any of 26 to 35cable channels. The converter translates theincoming signal selected by the subscriber to aVHF frequency the best suited to reception bythe television set. Thus, with a converter, a sub-scriber may receive from 26 to 35 channels froma single cable. Greater channel capacity can beachieved by using both multiple cable and conver-ters.

The converter rests on top of the televisionreceiver and takes the place of the receiver's tun-ing mechanism (see Figure 10). Current versionscost about $23 to $35 each.

Figure 10. A Switched Converter.

C. Broadband CommunicationsCable's Future

Modern cable television has evolved from aretransmission system providing basic receptionto an expanded medium for delivering one-wayservices to subscribers. With the addition ofimported signals, au tomated origination, and localprogramming, cable television has surpassed thecapabilities of broadcast television and is well onthe way to becoming the "television of abun-dance" envisioned by the Sloan Commission.'

Cable technology promises two-way communi-cations for subscribers, and the potential of broad-band communication networks in the future.

THE EVOLUTION OFCABLE TECHNOLOGY:TWO-WAY COMMUNICATION

Cable's most glamorous aspect is its "bi-directional," or two-way, capability. For the mostpart, this capability exists now only in prototype.Little is known about the future market for two-way communications; system operatoi ,, there-fore, are likely to be cautious when consideringinvestment in two-way equipment.

Two fundamental kinds of two-way systems areenvisioned for cable communications: institu-tional two-way systems for a few users, and sub-scriber systems for all subscribers. Institutionaltwo-way systems may involve two-way data com-munications or two-way video communications.Most of the electronics for these systems arealready on the market.

Subscriber systems involve three prospectivelevels of capability.Subscriber response systems - very limited, partyline digital communications between subscriberterminals and a computer at the headend, permit-ting such services as opinion polling. These sys-tems exist in prototype and should soon be markettested by several multiple system operators(MSO's). They may be available commercially intwo to three years.Subscriber initiated systems - expanded digitalcommunications between advanced terminals andthe headend. This approach may permit computerassisted instruction, remote facsimile reproduc-tion, or other services. An experimental systemof this type has been constructed in Reston, Vir-

'On the Cable: The Television of Abundance, Report of theSloan Commission on Cable Communications, Edward S.Mason, chairman (New York: McGraw-Hill Book Co., 1971).

ginia. They are likely to be available commerciallyin less than six years.Switched video communications exists commer-cially; the telephone company offers limitedswitched video communications (video telephoneservice) in Chicago. Two-way video telephone ser-vice is not suitable for cable television systems,because cable distribution systems do not havesufficient switching facilities, and cable systemsare not widely interconnected.

In the next few years, only subscriber responseand closed circuit services are likely to be offeredon cable systems. Later, subscriber initiated ser-vices may be available. The technical descriptionthat follows deals with each of these kinds of ser-vices.

Headend

For subscriber response systems, the majoradditions to the headend will consist of a compu-ter to control communications with subscribers,and many more interconnection facilitiesperhaps including links with satellites to con-nect the local cable system with (projected)national video and data networks. The computerwill send short, individually addressed electronicmessages to each of thousands of subscriber ter-minals. Each terminal will respond with short datamessages back to the computer at the headend.The responses would indicate the status of theterminal, which might include the channel beingWatched, subscriber requests for information,subscriber responses to questions posed by a tele-vision snow, or the status of a remote monitoringdevice such as a water meter or fire alarm. Theexchange of messages between headend compu-ter and terminals will take place in split seconds.

Distribution System

The electronics for two-way transmission arequite straightforward, if two cables are used.Amplifiers in one cable boost signals in the for-ward direction (headend to subscriber); amplifiersin the other cable boost signals in the return direc-tion

Two-way signal transmission in the same cableis more complex. A housing which contains a cableamplifier is enlarged to permit these additionalcomponents:

A second amplifier, to strengthen signals beingsent upstream

A pair of electronic filters, which separate thesignal traffic by routing one set of frequencies

15

to one amplifier, and the other frequencies to theother amplifier.

Depending upon planned uses, the filters maypermit either a roughly equal number of upstreamand downstream channels (a "midband split"), orthe majority of the channels about 35 down-stream with a few three or four upstream(a "subband split"). Figure 11 illustrates the dif-ferences in spectrum use.

The choice between these two methods of con-trolling electronic traffic in the cable dependsupon planned use. Midband split arrangementsare intended for closed circuit uses; there are alarge number of upstream channels. The subbandsplit arrangement permits 35 channels down-stream and only four upstream; it is designed forsubscriber response systems.

Subscriber Terminals

Advanced systems depend heavily upon the useof sophisticated home terminals that will include,besides the television receiver, such equipmentas facsimile printers, computer keyboards, andvideotape recorders. Most subscriber services arepredicated on a system of limited subscriberreturn communication called a "subscriberresponse" system. A small push-button terminalin the home (similar to a touch-tone telephonekeyboard) receives periodic data messages fromthe headend computer. A separate message isaddressed to each subscriber terminal. The ter-minal, as shown in Figure 12, responds with a shortdata message upstream to the computer, whichinterprets and stores the messages from each sub-scriber. Since the messages are short, manythousands of them can be sent in sequence overthe cable. Current versions of this system, nowbeing tested, involve a computer which can inter-rogate as many as 30,000 subscriber terminals in22 seconds.

Subscriber response systems, though limited todigital communications between the headendcomputer and subscribers, will permit severalunusual kinds of services:

Opinion polling. Subscribers indicate their opin-ion regarding an issue posed on a cablecastprogram. The results are tabulated by the compu-ter and presented to those televising the program.

Home shopping by cable. Retail shops lease achannel and display goods to subscribers, whomay make orders by keying ordering instructionsinto their terminals. The goods are later deliveredand the customers billed by the cable system.

16

Upstreamsignals

MIDBAND SPLIT

Crossoverfilters

Downstreamsignals

willamm4111

16 ReturnChannels

23Channels

5 30 54 88 108

SUBBAND SPLIT

160 174 216 MHz 300

Upstreamsignals*"signals*"

Crossoverfilters

Downstream...4..signals

4Return

Channels

5

Low VHFChannels

(2-6)

FM

Channels

9

Mid-BandChannels

7

High VHFChannels

(7-13)

14Super-Band

Channels

5 30 54 88 108

Figure 11. Difference in Spectrum Use

Pay television. Some channels will be scrambled,unless unscrambled by a command from theheadend computer. A subscriber may view firstrun movies or other special programs, paying afee-per-program, by indicating to the computerthrough the home terminal to unscramble the paytele% ision channel. The subso:ber is billed at theend of the month.'Remote sensing. The headend co -nputer recordssignals sent via the home terminal from fire andburglar alarms, or automatic reading of utilitymeters.

At a considerably higher level of technicalsophistication and cost than the subscriberresponse system is the "subscriber initiated"

Figure 12. A Subscriber Response Terminal.

174 216 MHz 300

system. On this level of service, communicationbetween subscriber terminals and headend com-puter is greatly expanded, though still digital. Thesubscriber may initiate communications by send-ing data messages to the computer, rather thanwaiting to respond to computer electronic inter-rogation. This gives rise to potential uses suchas computer assisted instruction, random accessto library materials (assuming they have been con-verted to digital form), ticket reservations, direc-tory services, and catalog shopping. In additionto the television receiver, subscriber initiation ter-minals might include several other devices, suchas a remote printer, a video tape recorder, anda full alphanumeric keyboard. One conceotion ofsuch a terminal is shown in igure 13.

Implementation of all 'wo-way services is stillat the experimental level. The necessarytechnology is reasonably well developed, but themarket for services is not known and the costsconnected with providing them are hard toestimate. Cable hardware costs are easily deter-mined; but nearly all two-way applications requirethe use of computers. The cost of programmingthese and the computer associated software maybe a critical factor in the economic feasibility oftwo-way applications. Another important element

'Pay TV can be provided without subscriber response capabilityin the cable system. Several different systems which do notrequire two-way capability are being market tested.

is the cost of terminal equipment in the sub-scriber's home. One-way cable requires only atelevision set and perhaps a convener. Presentestimates of the cost of terminal equipment foreach home indicate that subscriber two-way ser-vices will be very expensive. However, technologi-cal advances and mass production techniques mayreduce terminal costs to economically feasiblelevelsas they did in the production of televisionreceivers and subscribers may well be willingto pay more if they feel the services provided areworthwhile.

Institutional Two-Way Systems

Subscriber services are limited because of thelarge number of users. If, for example, all sub-scribers were equipped with conventional videocameras as part of a video telephone system, 20two-way video conversations would exhaust thecapacity of a single cable.

However, if there are few users, a full rangeof communications services, including two-wayvideo and high speed data, can be offered. Appli-cations of this kind are called institutional usesbecause they are normally operated outside thegeneral home subscriber network, as for example,in businesses, schools, hospitals, or publicagencies. But, if an institutional function does notuse many channels, it may be provided on someof the unused frequencies of the main distributionsystem. Uses which require a large number ofchannels are best provided with a private cableconnecting the few users.

Some of the projected services for closed circuituses are:

Figure 13. One Conception of a Subscriber Initiation SystemTerminal.

17

Two-way vioeo. As an example, a video linkbetween a doctor and a paraprofessional who islocated at a remote medlual clinic could be usedto improve health care in aural areas.Data interconnection. A computer in one depart-ment of a city could be interconnected to anotherdepartment's computer. Banks and branches, hos-pitals and clinics, downtown retail stores and sub-urban branches each have data interconnectionneeds.

FUTURE COMMUNICATION SYSTEMSAN THE CONVERGENCEOF TECHNOLOGIES

How well two-way approaches meet the test.ofthe market depends not only upon cable televisiontechnology, but also upon the parallel develop-ment of competing technologies. Cable televisionis neither the only new develop,:ient in moderntelecommunications, nor the answer to all com-munications needs. It is worthwhile here toexamine what things cable cannot do, and to notedevelopments in competing technologies as well.

Capacity Limits

Theoretically, there are no real limits to cablecapacity: new capabilities can be purchased inblocks of 40 channels simply by adding morecables. In practice, however, cable is limited tothe capacity that can be provided competitivelywhen the costs of other modes of telecommunica-tions are considered.

Systems equipped with subband split subscribertwo-way electronics (see page 13) are not suitablefor widespread use of two-way video. Typically,2,000 or more subscribers would share the threeto four return video channels on a single feederequipped with subband split amplifiers (35 chan-nels downstream, three tc four channelsupstream). Even closed circuit cable with midbandsplit amplifiers permits only 16 channels ofupstream video signals.

One frequently mentioned use of cabletechnology would permit an individual subscriberto request a specific videotape from a library oftapes. This application must be viewed in termsof the number of potential downstream channels.While current systems may have reserve capacitiesof 20 to 30 channels per cable, the sharing of thesedownstream channels by thousands of subscriberscould quickly exhaust the resources and createa shortage of channels. Clearly, a typical cable

18

system could not expect to respond to the requestfor the simultaneous viewing of more than a fewtapes, certainly not hundreds, before all the avail-able downstream capacity was exhausted.

It the demand for these types of servicesbecomes high, additional capacity could beinstalled. But, for the near future, cable systemsmay not be installed with such additional capacity.Further, there are limits to the number of cablesthat telephone poles and underground ducts cancarry.

One means to increased capacity, where con-tinuous motion video is not required, is in theuse of "frame-stoppers," which permit timeshar-ing of a video channel. A television picturejust as a motion picture consists of a seriesof still pictures or "frames." Every one-thirtiethof a second a new frame is transmitted elec-tronically. Each frame is a complete picture. Ifthere is no movement in a TV picture then eachframe transmitted is the same as the previousframe.

A frame-stopper terminal receives a frame, dis-plays it on a TV screen as a normalTV set does,and stores it electronically. Then instead of receiv-ing the next frame transmitted as an ordinary TVset does, the frame-stopper ignores the new frameand replays the stored frame for a specifiedperiod. It is possible to electronically "address"a frame as it is being transmitted. A frame-stopperterminal can then look at the address on eachframe and receive only those frames addressedto it.

Thus, if all subscribers are equipped with frame-stoppers programmed to replay a stored framefor 10 seconds, 300 subscribers can view still pic-tur,r) addressed individually, using only one tele-

n channel. This mode of "slow speed tele-vision" would be use;ul for such applications ascomputer-assisted instruction, remote catalogshopping, or listing poison antidotes.

Frame-stopping technology is still in a state offlux and no commercial firm has yet mass pro-duced a low cost frame-stopper, (under $100 perterminal), although $500 to $700 per terminal nowappears to be a feasible cost.

Most future subscriber applications discussedin the general literature, like frame-stoppingtechnology, require the use of sophisticated hometerminals. To date, no inexpensive units have beendeveloped. As currently projected, home termi-nals would range in cost from $90 to $300 lessconverter (converter costs are $30 per subscriber).Widespread implementation of two-way cable ser-vices is dependent upon the development ofhighly reliable, low cost terminals.

New transmission mediums

A frequently suggested "cure" tor more capacityis new transmission mediums. Two that have beenfrequently mentioned are wave guides and fiberoptics. Both hold promise of huge channelcapacities.

Wave guides are carefully fabricated hollowmetal tubes which efficiently carry Super HighFrequency radio waves. Potentially, wave guidesmay carry from 400 to 800 television channels ofcapacity.

Fiber optics involve transmission of lightthrough very thin glass fibers. The light signalsare coded to carry television signals or data infor-mation which are carried by the light beam asit travels th rough the fiber. The bandwidth capac-ity of optical fibers is breathtaking as many as2,000 television channels or more.

Both systems are in the develcpment stage. Cur-rent work on wave guides is several years fromfruition and is designed to provide long distancetelephone transmission. Several characteristics ofthe current work make it totally unsuited for localdistribution of TV signals. The use of fiber opticsfor transmission is evolving rapidly, but develop-ment of devices to connect the fiber lines toheadend or terminal facilities is lagging. Develop-ment of a broadband communications system withfiber optic transmission may be 5 to 10 years away.

It is possible that coaxial cable will becomeobsolete, but the role of cable television as abroadband local distribution communications sys-tem will remain for the foreseeable 'future.

Prospects for SwitchedVideo Communications

Cable television communication with a treeshaped distribution system is an awkward basefor the development of a fully switched networkthat will allow one subscriber to dial another, aswith the existing telephone network. It does notuse local exchanges which permit flexible and reli-able connection between random subscribers,except through the headend. A cable televisionsystem may never be convertible to a switchedbroadband network, without costly rebuilding.

Further, the cost of a completely switched videotelephone system service nationwide would beextremely expensive. One estimate is $12,000 persubscriber (as compared to $600 per subscriberfor the existing telephone network). Any decisionto build complete video switching between allsubscribers would involve a national policy com-mitment of at least the magnitude of the Interstate

Highway System. The switching capability that iscurrently feasible is based upon very limitedaccess because of the small number of upstream(subscriber to headend) video channels. A fewmanufacturers have produced hardware thatwould provide for limited switching but the pro-jected costs have been two to eight times the costof unswitched cable systems and so have not beenpopular with cable operators.

Other Communications Media

Other telecommunications media offer some of-the same services envisioned for cable television,notably pay television and data transmission. Thefirst pay television services were offered commer-cially via Multiple Distribution Service (MDS) mic-rowave. MDS broadcasts television signals to spe-cial receiver systems of the type that couldeconomically serve a number of TV sets at a singlelocation such as motels, hotels, and apartmentbuildings.

The telephone system already provides datatransmission service. In addition, the telephoneindustry is building an all digital network whichwill eventually lower the costs of data transmis-sion. Other companies have-been created to serveas specialized common carriers and will providea digital network for computer communications.In such systems, however, cable may still serveas the local distribution system between the car-der and the subscriber.

SUMMARY

Cable television has evolved from a retransmis-sion medium as traditional CATV, to modern cabletelevision an important and exciting mediumon its own merits. Most of cable television'stechnical magic lies in the future. But its presentcapacity to deliver an expanded "menu" of one-way video programming results from majortechnological developments in the past 10 years.

In the near future, subscriber response anddosed circuit two-way developments are likely tobe developed and perfected, opening prospedtsfora vast new range of services. In the more distantfuture, broadband communications may movefrom coaxial cable to a new medium, such as opti-cal glass fibers, or some yet undiscoveredmedium. But regardless of its mode of transmis-sion, cable television as a local broadband dis-tribution system is likely to remain in existencefor the foreseeable future. Plans and decisionsmade now by franchising authoritie.; are unlikelyto be invalidated by rapid technological evolution.

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II. MAJOR ISSUESFOR FRANCHISING AUTHORITIES

Understand;ng cable technology is important tolocal officials because they are faced with technicaldecisions about cable television in their com-munity. This part of the report examines threekinds of technical questions local officials mustdeal with.

Design decisions must be made before anyoperator is franchised, and are nearly irreversibleonce the system has been constructed.

Performance issues must be decided beforefranchising, but they also present a continuingresponsibility to the franchising authority forensuring that performance standards are met.

State of the art issues cannot be resolved sincethey will be future problems. However, local offi-cials must decide what mechanism they will createin the franchise to ensure that the franChisingauthority has a role in keeping the systemtechnologically up-to-date.

A. Design Decisions

Some design decisions are of such importanceto the community that they should not be leftentirely in the hands of the system operator. Localofficials ought to take a large share of the responsi-bility for making decisions on at least these sixquestions:1. What kinds of facilities should be constructedfor public use of the system?2. How much present and future capacity shouldbe built into the cable system?3. What kind of two-way facilities should be instal-led at the outset?4, How should service areas be defined?5. What interconnection capacity is needed?6. What can be done to extend service to lessdense areas?

Local officials are not required by the FCC toanswer each of these questions, but failure to doso leaves the decisions entirely in the hands ofthe system operator. Once made, the decisionsare often practically irreverFioe because of thehigh cost of cable system pint and installation.

WHAT KINDS OFFACILITIES SHOULD BECONSTRUCTED FOR PUBLICUSE OF THE SYSTEM?

The commission's rules require only that cableoperators in the 100 largest television markets fur-

20

ni5h channel space for access cablecasting, andmaintain production ,iacilities within the franchisearea for use on the public access channel.'However, the system operator may also agree tofurnish equipment as a condition of the franchiseagreement and it is in the interest of the franchis-ing authority to develop specific priorities offacilities desired before a franchise is granted.Further, the full public value of a cable systemwill not be realized without investment in publicfacilities, such as educational programmingstudios, that will not be provided by the systemoperator. Local authorities interested in promot-ing the publicservices on cable television will havcto plan for thedevelopment of additional facilities,the manpower to use them, and the money topay for them.

For policy planning purposes, facilities for thecable systems fall into two general categories:

Studios and equipment for public access andlocal origination

Other public facilities.

Studios and Equipment forPublic Access andLocal Origination

The origination facilities provided by a systemoperator should be designed to meet the needsof the community served. The range of studiooptions is so broad that facilities can be designedonly after the franchising authority has weighedits planned uses against capital costs. The costsof live studio facilities, whether owned by the sys-tem operator or the community, vary enormously.The following figures illustrate some possibilities.

Low Cost Black and White Studio - $25,000Two live black and white camerasOne 16mm film chainThree 1/2" black and white portable video

tape recorders and camerasModerate Cost Black and White Studio - $50,000Three black and white studio camerasFilm projectorSlide projectorStudio lighting and equipmentSpecial effects generatorTwo 3/4" video tape recordersTwo 1/2" portable recorders and camerasModerate Cost Color Studio $150,000Three color studio camerasSpecial effectS generatorControl room electronicsFilm and slide projectorsTwo color video tape recordersThree black and white video tape recorders

'Cable Television Report and Order, 47 C.F.R. 76.251(a)(4),(1972).

Test equipmentStudio lighting and equipment.It should be emphasized that these studio pack-

ages represent a relatively at,stere investment incomparison with broadcast studio facilities, whichmay run into $1 million or more. Further, thesefigures represent only capital outlays. Operatingexpenses can easily total from $20,000 to severalhundred thousand dollars a year. Planning forstudio facilities, therefore, should include carefuloperating budgets as well as capital costs.

Other Public Facilities

Many communities tend to think of public cableservices in terms of the three access channelsdefined by the FCC's rules. However, cable televi-sion systems offer exciting possibilities for closedcircuit uses that may enhance the quality of in-school education, health services delivery, andother public services. Planning for such pos-sibilities involves consideration of a broad rangeof terminal equipment. Listed below are someillustrative examples.

School FacilitiesTaps to each schoolTaps to each classroom (far more expensive)Videotape recordersStudio facilities for local program production

within the schoolClosed circuit network connecting all schoolsFacilities to permit school studio programming

to be distributed to all subscribers

Hospital FacilitiesPatient room tapsOperating room studio equipmentClosed circuit interconnection of hospitals and

clinics

Library FacilitiesVideotape recorders and tapesCamera equipment.

HOW MUCH PRESENT ANDFUTURE CAPACITY SHOULD BEBUILT INTO THE CABLE SYSTEM?

Most discussions about cable system capacitycenter on channel capacity of the distributionsystem. But distribution capacity questions are dif-ficult to resolve without an estimate of local prog-ramming demands on thesystem. For example,a ten channel local education network, in conjunc-tion with TV signal carriage, would nearly saturatea 35 channel system. Decisions about present andfuture channel capacity should be made in con-junction with estimates about the development

of various sources of local users. Unfortunately,it is very difficult to develop meaningful estimatesabout corqmunications uses that presently existonly on a very small scale. FCC requirements foreducational, government, and public access chan-nels providi? little guidance for the developmentof future programming.

Further, system operators tend to view importedsignals as more attractive offerings to subscribers,than local programming. Thus, the developmentof local programming will depend on the qualityof local planning and interest.

There is no proven method for accuratelyassessing the elements of any community whichwill make use of local programming. Not manyexamples of productive uses exist, and few localinstitutions are in a position to plan precisely howthey will use such an unknown resource. Localofficials are faced with very difficult choices aboutcapacity demands, and the elements of thechoices are not clearly defined.

Local officials can, however, consider the costof system capacity, and weigh it against an assess-ment of the number of users in the communitywho will make use of local programming. Anyassessment is bound to be uncertain andspeculative, since few potential users will be ableto predict accurately what demands they will makeon the system. Nonetheless, an informal canvass

of public school or university activities andresources, for example may give local officialsa sense of some of the demands that will be placedon system capacity. Decisions about capacity maytiien be more informed.

Local officials should also consider the cost ofsystem capacity, since costs ultimately will bereflected in both subscriber rates and theeconomic viability of the system. In the discussionthat follows, distribution alternatives are

Figure 14. A Single Trunk Single Feeder System without aConverter.

21

examined in terms of capacity now and in thefuture and cost implications. The special caseof low cost service to less dense areas is evaluatedlater in another section.

Within present cable industry practice, there arefive primary methods of sending signals from theheadend to the individual subscriber; four ofthese methods comply with FCC requirements forthe top 100 television markets, and the fifth is

suitable for cable television systems outside themajor markets. Since all cable systems consist oftrunk cable and feeder cable, the major distinc-tions between these alternatives involve thenumber of each type of cable required to providecustomer service. The alternatives are:

1. Single Trunk Single Feeder (see Figure 14).A single electronically active trunk cable is laid

from the hub to the neighborhood; a single activefeeder cable is then laid past each home; a singledrop cable enters each home and is connectedto the subscriber's television set.

"Active" cable is installed with the necessaryelectronics to carry electronic signals in one orboth directions. The electronics, depending uponthe cable's purpose, include amplifiers to boostsignal strength, splitters to divide the signal at thecable junction, taps to draw the signal into thesubscriber's home, etc.

The capacity of this system is restricted by thecapacity of the television receiver 12 channels.This system does not satisfy FCC requirementsfor systems in the 100 largest television markets,although it might be appropriate for smaller sys-tems outside the top 100 markets.

2. Single Trunk - Single Feeder -Converter (see Figure 15).

A single active trunk cable is laid from the hubto the neighborhood; a single active feeder cable

4

Figure 15. A Single Trunk Single Feeder System with aConverter.

22

is then laid past each home; a single drop lineenters each home; and a home converter isattached to each subscriber's TV set.

The capacity of such a system standard coaxialcable with available converters is approximately26 to 35 channels. Installation of two-way elec-tronics permits four channels to be carried froms. -ribers back to the headend. Current design

J aches within the industry are probablyre6,..dng a consensus that this option is a relativelyinflexible alternative, not permitting economicalfuture expansion.

However, there is a legitimate argument for thisalternative. If u'ile services develop slowly, thenit will be less expensive to install one cable andwait to install another cable until uses are gener-ated. In other words, this argument asserts thatbecause of the time-value of money despiteinflation and higher installation costs the dollarsinvested in the future might be less than the costof installation of the second cable presently.

If local officials should prefer a single cablesystem, the principal financial impact of such achoice would be

lower capital costs; andthe probability that the system would earn an

acceptable return on investment.3. Dual Activellnactive TrunkSingle FeederHome Converters (see Figure 16).

This distribution syStein includes two trunk cab-les; however, only one of the two contains theelectronics necessary for signal transmission. Theother, a "shadow" cable, contains no electronics.The system includes a single active feeder cable,and a home converter which substitutes for thetelevision set's channel selector. This system iscapable of delivering 26 to 35 channels to the homeat the time of installation.

.14

Figure 16. A Dual Trunk Single Feeder System with aConverter.

Installation of two-way electronics again permitsfour channels from subscribers to the headend.With the installation of midband split, two-wayelectronics, the second trunk cable may be usedfor closed circuit uses. This arrangement providespoint-to-point communications up to 23 channelsdownstream and 16 channels upstream4. Dual Active TrunkDual Active Feeder -A/8 Switch (see Figure 17).

This distribution system includes two activetrunk cables, two active feeder cables, and aswitch at the home TV set enabling the subscriberto switch from cable A to cable B. In order toselect one of 12 channels on each cable, the chan-nel selector on the set is used.

The theoretical maximum channel capacity ofthis alternative is 24 channels. The actual max-imum is often less since a strong off-the-air signalcauses interference to the signal carried on thesame channel in each cable. With three or morestrong local VHF stations, the maximum numberof channels that can be obtained with dual cableis less than 20. Thus, this alternative has, in theshort term, relatively low channel capacity. Expan-sion to high capacity in the future is relatively easy,with the addition of a converter (provided the sys-tem is initially constructed with electronics cap-able of carrying 35 channels of signal bandwidth).Except in very densely populated areas, this alter-native involves higher capital costs per user thanthe other alternatives.5. Dual Activellnactive TrunkDual Active/Inactive' FeederHome Converter (see Figure 18).

This distribution system, like the previous alter-native, includes two trunk cables and two feedercables. However, only one trunk and one feedercable are active; the other trunk and feeder cablesare inactive. The system includes a converter andis thus capable of delivering 26 to 35 channelsto the 'dome immediately. Expansion to 70 chan-nels per subscriber is made possible by the addi-tion of electronics to the second cable.

'A number of the issues involved here are matters of contentionwithin the cable industry. Particularly controversial are thegeneral choices between #3 and #4 above. Choice #3 requiresa high number of subscribers per mile to be immediately com-parable in costs. On the other hand, choice #3 is easily expan-dable. Choice #4 involves the use of converters which areundergoing rapid technical evolution and whose maintenancecosts are in doubt and expansion requires adding elec-tronics. Yet, choice #4 yields more immediate capacity. Themost accurate general statement that can be made is that anappropriate choice depends in part upon the particular com-munity, in part Upon the development of converters and cableelectronics, and in part upon the speed with which new usesrequire the expansion of cable capacity.

Figure 17. A Dual Trunk Dual Feeder System with an A/BSwitch.

The distribution alternatives are summarized inTable 2. An important aspect of each of these dis-tribution alternatives is a basic fact of constructioneconomics: although cable and electronics costthe same regardless of when installed (discountinginflation), installing a second cable along with thefirst is far cheaper than installing it later.

Alternatives #3 and #5 make use of these con-struction economics. Each has dual trunk cables;in addition, alternative #4 has dual feeder cables.A dual trunk-single feeder system includesshadow trunk and shadow feeder cables. Thereis a substantial difference between the two alterna-tives in terms of capital costs as well as expecta-

Alternative

23

Figure 18. A Dual Trunk Dual Feeder System with aConverter.

tions about the development of future servicesand capacity needs.

Depending upon geographical layout and den-sity, a cable system will require from two to fivetimes as much feeder cable as trunk. Thus, theinstallation of a second feeder cable is expensiveno matter when it is undertaken. If a shadowfeeder cable is installed at the outset, distributioncosts, including cable, increase about 20 to 40 percent. But if the second feeder is installed at a laterdate, it will cost at least twice as much as thefirst feeder.

This dues not imply that activating the secondcable will be easy or inexpensive. Conversion of

Table 2. Distribution System Alternatives

Capacity Expansion withoutRebuild

1. Single Trunk-SingleFeeder

24 channels or less tosubscribers

35 channels to subscribers;4 channels subscriber return

2. Single Trunk-SingleFeeder - w/Converter

35 channels tosubscribers

4 channels subscriber return

3. Dual Trunk-SingleFeeder - w/Converter

35 channels to subscribers;some institutional two-way

35 channels to subscribers;4 channels subscriber return;institutional two-way

4. Dual Trunk-Dual Feeder

24 channels or less tosubscribers

35-70 channels to subscribers;4 channels subscriber return;institutional two-way

5. Dual Trunk-DualFeeder-w/Converter

35 channels to subscribers;some institutional two-way

70 channels to subscribers;4 channels subscriber return; orinstitutional two-way

24

shadow to active trunk involves not only the instal-lation of, both forward and reverse trunkamplifiers, filters, and accessories, but also theconnection of feeders from cable A to trunk cableB and adjusting cable Li electronics for two-way.

The second feeder decision involves more thanfinancial outlays. A dual trunk-single feeder sys-tem can accommodate subscriber response -two-way technology without a second feeder. Themain "downstream" trunk is retained for one-waydelivery of 35 channels to subscribers. When elec-tronics are installed in the second trunk, and itis connected to the feeder, subscriber responsetraffic can be carried back to a computer installedat the headend. The second trunk is two-way, andthus can also be used for two-way, point-to-point(closed circuit) uses.

The use of the second trunk cable for closedcircuit applications is limited by the fact that trunkpasses only about one-quarter of the homes andbuildings in a city; the remainder are reached withfeeder cables. Unless a prospective closed-circuituser is located near a trunk, he cannot use theservice. The cable industry, for the time being,solves this problem by extending the second trunkto areas where closed circuit users are located,or by installing a special feeder.

But; in general, it is difficult to predict prospec-tive dosed circuit users and the kinds of servicesthat wiil be required. If the decision is left to thesystem operator, extra trunk or a second feedercable may be installed only to those places whereclosed circuit users have been clearly identified.

That decision is properly one for the franchisingauthority, not the system operator. The greatexpense of a second feeder, installed later, wouldnaturally make a system operator reluctant toundertake the investment, regardless of the city'sneeds. If the franchising authority anticipatesgreat educational or local government demandsfor closed circuit uses (or more than 35 channelsof subscriber services), it may wish to require theimmediate investment in a second shadow feeder.

To summarize these arguments:

Single trunk and feeder systems, althoughlimited in expansion capacity, are less expensiveoptions and do not require investment in cablethat might not be used.

Converters are more economical for systemswith few subscribers per mile; A-B switches area better initial step for systems in denselypopulated areas.

The decision to invest in a second feederdepends upon judgment as to which kind of two-way services will develop most rapidly: closed cir-cuit uses, or subscriber services.

HOW MUCH TWO-WAYCAPACITY SHOULD BEINSTALLED AT THE OUTSET?

Subscriber two-way systems are still in the pro-totype stage, and, for the time being, few com-munities will enjoy subscriber response service.There are, however, several other ways that two-way cable communications can be employed pre-sently. They can be conveniently grouped in threecategories:

Two-way systems for origination at locationsaway from the headend

Two-way closed circuit systemsCommunity information and service center

systems.

Origination Away from the Headend

There are two means by which programs canbe originated away from a. main studio: mobilevans, and remote studio facilities.

A mobile van permits origination virtually any-where, but programs cannot be carried live with-out a microwave hookup to the headend.Similarly, a permanent studio cannot originate liveprograms if it is not connected electronically tothe headend.

The franchising authority must decide whetherlive programming uses planned for originationfacilities justify the costs of interconnection withthe headend for live programming. Even if thereare no formal cablecasting facilities, originationfrom such places as high school basketball gym-nasiums may warrant installation of the cable topermit live cablecasting.

Institutional Two-Way Systems

Two-way services such as data interconnectionand video teleconferencing are feasible on cable,providing the number of users is limited. Institu-tional uses can be provided on unused channelson the main system of cables, or by designatingparticular cable for institutional users. Forexample, each of 40 schools or libraries might beassigned a channel on a cable interconnecting allof them. With studio facilities at each school, anyschool could transmit to all the others. Or, alter-natively, as many as 20 video conferences betweentwo schools (for debates, for example) could takeplace simultaneously.

Hospitals and local clinics might be intercon-nected to permit remote diagnosis (video signalsfrom the clinic to the hospital), orto permit remoteobservation of complex surgery (video signalsfrom the hospital to clinics).

Community Information and Service Centers

Three prOblems have become apparent to manyof those concerned about cable's possible publicbenefits.

Not everyone will subscribe to the systemTwo-way services which seem to have great

public possibilities will be activated on a largescale only upon evidence that they can makemoney

Implementation of two-way s.-Irvice requiresexpensive terminal equipment in the homes ofsubscribers.

These problems, taken together, mean that thepublic benefits of cable television may not be avail-able to those who need them most, and that themost interesting public uses those involvingtwo-way cable may have to wait (or the develop-ment, of profitable commercial uses. In the mean-time, local officials might consider the possibilityof establishing public community information andservice centers.

Such centers could provide a central point towhich citizens could bring questions and prob-lems relating to a wide variety of governmentalservices, linking the public to local governmentand public service agencies via two-way communi-cations systems. They would make cable TV freeto those who could not afford it, ensuring that100 per cent of the population could receive publicservices by cable television. They might allow thelimited introduction of two-way services; and theymight assist in making local government moreresponsive and comprehensive.'

The information and service centers wouldprobably have their greatest value and most useif they were located in multipurpose communityfacilities. A neighborhood center combining adulteducation, recreation, library services,. meetingrooms, social services counseling, and othermunicipal services would be an optimum choice.

Cable receiving facilities could be arranged forindividual and group viewing (see Figure 19). Andtwo-way terminals could be situated in carrelsaffording user privacy but allowing for easy accessto assistance when needed. A small number of

'See Alan R. Siegel and Calvin W. Hiibner. Special Servicesto Neighborhood and Home: A Community Telecommunica-tion Demonstration Concept, Paper for the internationalTelemetering Conference, October 10, 1972. Siegel, director,and Hiibner, program analyst, Community Environment andUtilities Technology Division, Office of the Secretary forResearch, and Technology, U.S. Department of Housing andUrban Development, state in a footnote that neighborhoodfacilities under specified circumstances are eligible for federalsupport for up to three-quarters of facility construction. SeeTitle VII, Housing and Urban Development Act of 1%5, 42U.S.C. 3101.

25

terminals could be located in each center initially,with the ability to increase the number as demandwarranted. A one-way only receiving point wouldrequire merely a television-set preferably color

and a converter; a two-way terminal :would,in addition, have an electronic keyboard,headphones, and auxiliary electronic equipment.Audio and video cassette machines could besituated on carts and checked out when needed.

Figire 19. A Community Information Center Terminal.

The MITRE Corporation, which has done exten-sive research on remote access to computers viacable and on computer assisted instruction, hasestimated the cost of such a system:

Excluding system integration and installationcosts, but including the cost of the computerand all required hardware for audio, colorand video tape capabilities, the pro-rated costamounts to $3,600 per terminal ... If a moder-ate (25 systems) number of systems were con-structed in mass in 1975, the total cost of thesystem will fall to $2,000 per terminal andprobably further.2These figures do not include software develop-

ment costs which usually represent the "hiddenpart of the iceberg" in programs of this kind.

Activation of two-way capability on a wide scalerepresents a substantial investment in system elec-tronics and home terminals, It is not likely to beundertaken except on the expectation of adequatereturn. At the present time, there is no convincingevidence to support such an expectation.

'Toward a Market Success for CA! An Overview of the TICCITProgram (McLean, Virginia: MITRE Corporation, June, 1972).An excellent discussion of computer assisted instruction.

26

An intermediate step that might be consideredwould be to first implement two-way service onlyto community information and service centers.This would both lessen the investment in hard-ware and share the benefit of that investmentamong a large number of users. Information cen-ters could then test the feasibility and publicacceptance not only of social services on cablebut of many commercial services as well.

HOW SHOULDSERVICE AREAS BE DEFINED?

The actual layout of the cable distribution sys-tem is an important issue for the entire com-munity: the layout design will arbitrarily bringtogether or segment existing neighborhoods andcommunities of interest unless careful planningis performed in advance.

This character of the cable distribution layoutwill be reinforced if different parts of the cablesystem can, as the need arises, receive separateprogramming. This would be the case if the systemwere made up of several interconnected hubs.However, when a single system is equipped withrelatively inexpensive switching equipment at theheadend, it is possible to distribute programmingto subscribers connected to one of the system'smain trunks, without distributing it to subscriberson the other trunks. The area served by each maintrunk thus becomes a subdistrict, in which sub-scribers may receive programming transmittedonly to them.

This approach to localizing the programmingprovided by the cable system can be duplicatedby extravagant use of channel capacity. Localprogramming for a neighborhood can be providedsimply by designating a channel for that com-munity. However, that approach rapidly exhaustssystem channel capacity. Districting arrangementsconserve channel capacity by allowing channelsto be used over and over again in different partsof the system.

The boundaries of a trunk district are shapedprincipally by the technical limitations of cablesand distribution electronics. In practice, theselimitations are not overly restrictive. The feedernetwork connected to a single trunk extends ser-vice about three-quarters of a mile on each sideof the trunk. Thus, a trunk district can be as largeas 1.5 X 7-10 miles, or smaller, if desired (see Figure20).

Within those constraints, boundaries can fre-quently be defined to coincide with neighborhoodboundaries, school districts, or political jurisdic-tions. Of course, it is not mandatory that trunk

HEAD END

TRUNK -

FEEDERS

7 MILES

Figure 20. Subdistricts Defined by the Cable Television Distri-bution Layout.

districts be defined. Districting carries with it thepossibility that undesirable community bound-aries (such as railroad tracks which have separatedcommunities racially or by socioeconomic status)will become reinforced. If the franchising author-ity elects to define trunk subdistricts, it shouldthen consider locating origination facilities withinthe subdistrict, to permit local programming forresidents within that community to flourish.

If the cable system involves more than oneheadend, the franchising authority must make ser-vice area decisions. Fundamentally, there are twokinds of decisions involved.

Can (and should) the boundaries for a singlehub be defined to coincide: with other politicaland social boundaries?

Should the hubs be defined in terms that willpermit each hub service area to be franchised toa different owner?

The question of boundaries is not one oftechnology, but rather of local community feelingsand expectations about education and publicaccess programming. The second question, thatof multiple franchises, involves a different set ofissues mostly economic and organizationaland implies a positive role for experimentationand competition between types of ownership andmanagement. The few communities large enoug;,to face the prospect of a multiple hub system heldopportunities for making the cable system sociallymore productive, if intelligently planned decisionsare made.

WHAT INTERCONNECTIONCAPACITY IS NEEDED?

There are generally two interconnection situa-tions. Each involves vastly different proceduresfor solving the problems to be encountered even

though the technical means may be identical.Interconnection issues arise under these two cir-cumstances:

Interconnection of hubs within a multihub sys-tem serving a single city.

Interconnection of systems serving severaladjacent communities (a development that is likelyto increase as communities share educational cab-lecasting, etc.).'

Interconnection of hubs in a multihub systemis a design issue that should be planned anddecided upon before a franchise (or severalfranchises) is issued. The planning process is com-plicated by the fact that each kind of microwaveinterconnection mode imposes different FCClicensing requirements. In some cases, thefranchising authority has no regulatory rolebecause the microwave service is fully regulatedby the commission.

Interconnection of cable systems in separatepolitical jurisdictions differs procedurally frommultihub interconnection within the same juris-diction in two respects:

Interconnection is an issue that usually arisesafter franchises in each community nave beengranted. As a result, it is difficult to anticipate theprecise farm of interconnection requirements andprovide for them in each franchise.

Interconnection of systems under differentfranchising jurisdictions creates problems for localofficials, both in terms of planning and in termsof acting in concert. If no central authority existsto bring about agreement between systemoperators and each of the communities involved,planning for and developing interconnection mayturn out to be an extremely complex problem,one that is mainly political. For this reason, inter-connection of communities for exchange of localand regional programming may be appropriate forstate regulation.

This paper does not address the procedural dif-ferences between the two kinds of intercon-nection. Instead, it focuses on the specific techni-cal alternatives available to interconnect systemsfor different purposes.

There already exists a great deal of interconnec-tion for long distance carriage of television signals.This service is provided by the telephone com-panies and by specialized common carriers, whootter the service to both broadcast television net-works and to cable television systems.

'There is a third kind of interconnection for delivery of com-mercial programming in effect, cable networks. These arenot considered since franchising authorities have no jurisdic-tion.

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However, local interconnection is relativelynew. There are several different kinds of intercon-nection means, with different costs andcapabilities, and the regulatory framework foreach is different. The discussion that follows con-tains costs and capabilities of the basic possibilitiesand a description of the FCC's regulatory require-ments.

Cable

Headends can be linked with cable to provideas many c..annels as needed, one-way or two-way.Each cable can provide up to 40 channels one-wayat a cost of about $2,800 per mile, or 20 channelseach way for two-way at a cost of about $3,300per mile. The commission has not acted explicitlyto define its role in cable interconnection ofheadends.

Local Distribution Service Microwave (LDS)

With a single transmitter ($100,000) and multiplereceivers ($7,000 each), a system can distributeup to 18 channels one-way to many headends.Doubling the number of transmitters andreceivers permits up to 38 channels one-way. LDScould be used to provide 18 channels of two-wayservice between two headends, but it would nor-mally be more expensive than common carriermicrowave (see below).

The FCC regulates LDS fully in accordance withSection 78 of its rules. It licenses the serviceexplicitly for the distribution of signals from oneor more receiving points, from which the com-munications are distributed to the public by cable.

Long Distance Microwave

Chains of receivers and transmitters provideefficient point-to-point microwave interconnec-tion one-way or two-way over great distances. Atransmitter for one channel costs $10,000; thereceiver $5,000. This kind of service is suitablefor interconnecting a headend with a distantstation, but it is less efficient for interconnectionof several local headends serving contiguous dis-tricts.

The FCC regulates common carrier microwaveservice by licensing the carrier.

Instructional Television FixedService (ITFS) Microwave

This low cost service is designed to interconnectschools and colleges, but is occasionally used forother public services as well. A four channel trans-

28

mitter costs $36,000; each four channel receiver$500. It is clearly far less expensive than otherforms of microwave service.

The FCC fully regulates the provision of ITFSthrough Part 74 of its rules:

A license for an instructional television fixedstation will be issued only to an institutionalor governmental organization engaged in theformal education of enrolled students or toa nonprofit organization formed for the pur-pose of providing instructional televisionmaterial to such institutional or governmentalorganizations, and which is otherwise qual-ified under the statutory provisions of theCommunications Act of 1934, as amended.A nonprofit organization which would beeligible for a license for a noncommercialeducational television broadcast station isconsidered to be eligible for a license for aninstructional television fixed station.'Planning for capacity, as for distribution system

capacity, depends upon expectations about prog-ramming resources. If a multihub system is con-structed to provide programming at each hubheadend, then interconnection of hubs should betwo-way to allow programming to be distributedto the entire system from each hub.

If several communities interconnect to sharefacilities, such as a college television studio oraccess programming facilities, interconnectionneeds may be met with a multipoint one-way inter-connection system such as LDS or ITFS microwave.

Despite the regulatory jurisdiction problemsrelated to interconnection, planning by local offi-cials should consider interconnection in conjunc-tion with service areas and distribution capacity.these combinations should then be evaluated interms of present and proj?cted programming usesof the system, and plans should be orientedtoward adequate capacity iv handle anticipateddemands users will place on the system.

WHAT CAN BE DONE TOEXTEND SERVICE TOLESS DENSE AREAS?

Cable service cannot be economically feasibleif there are not enough subscribers to keep theshared cost of the cable distribution system low.In areas of low population density, cable servicehas often been economically infeasible in the past.New developments in amplifier technology permita decrease in per mile costs of distribution elec-tronics. In the future, as cable systems becometechnically more complex, the provision of serviceto small or sparsely populated communities

'47 C.F.R. 74.901 et seq., (1972).

becomes more expensive. Local officials facedwith the problem of low population density (e.g.,20 homes per mile) must be concerned withminimum service at lowest cost, rather than theprovision of excess capacity in the system forfuture use.

Recent technical developments permit signifi-cant opportunities to reduce the capital cost permile, and make the service available to more ruralsubscribers.'

Modern broadband solid state line extenderamplifiers are cheaper than older trunk amplifiers,and provide better performance. These line exten-ders are not as sophisticated as transistorizedtrunk amplifiers, but for small communities theywill provide up to 35 channels of service and theprospect of two-way subscriber response in thefuture, at a fraction of conventional costs.

A smaller system can use smaller size cable andlow cost line extender amplifiers spaced to pro-vide 35 channels of service. Further savings canbe achieved through the use of messenger cable

coaxial cable which has the supporting steelcable built into it. Table 3 below indicates thedifference in cost per mile of installed aerial cable:

Table 3. Cost Per Trunk Mile(for transportation and distribution)

3/4" cable using trunk & bridger amplifiers, typicalconstruction $4,500

1/2" messenger cable using line extendersonly $2,200

These savings can be achieved if the trunk cable,using line extenders, feeds subscribers directly.This eliminates added feeder cables and 3.cs3d-ated bridger amplifiers. It is sufficient for radialdistances of about two miles, feeding as manyas 100 homes per mile, as long as the homes arewithin approximate 300 feet of the trunk.

'Before the development of transistors (and, more recently,integrated circuits), high performance requirements madetube-type cable amplifiers very expensive. Cost savings wereachieved by lowerii:g performance requirements for the feedercable amplifiers (called line extenders). These amplifiers couldbe built to less stringent standards since they were not cas-caded excessively on the numerous short lengths of feedercable. The savings achieved were substantial overall, since somany line extenders were used in a system.

The distortions introduced by transistorized trunk andfeeder amplifiers are less than those generated in the finesttube type trunk amplifier a few years ago. Further, all modernamplifiers have a new circuit design (called "push-pull") whicheliminates a complex kind of distortion and permits the useof additional frequencies outside the standard 12 VHF chan-nels.

Savings in capital cost per subscriber are impor-tant to local officials only if they can be translatedinto lower subscriber rates, or provision of serviceto rural residents who live in sparsely populatedareas that otherwise would not receive service.

B. Technical Standards.

A second area in which local officials shouldmake decisions is that of technical performancestandards;' a malfunctioning system defeats thepurpose of good planning and design. It is possi-ble to leave the enforcement of system perfor-mance to the influence of the market place; thesubscriber, who is the ultimate consumer of cableservice, may discontinue service if the quality ofservice is poor. Theoretically, if the systemoperator begins to lose subscribers, he will makeattempts to improve the systems' performance.

However, there are several reasons why thefranchising authority should assume a role in thedevelopment and enforcement of technical stan-dards. In the first place, the technical standardsset by the Federal Communications Commissionin Subpart K of the February, 1972 Cable TelevisionReport and Order are not considered comprehen-sive by the commission. Moreover, they do notpreclude the establishment of more restrictiverequirements by local governments. In its recon-sideration of the Report and Order, the commis-sion stated:

The general question of federal pre-emptionof technical standards has been informallyraised by a number of parties. Our technicalstandards provide only a start. They will beexpanded to meet changes in the state ofthe art. We see no reason why franchisingauthorities may not now require morestringent technical standards than those inSubpart K.2

Franchising authorities faced with decisionsimmediately may not wish to wait for furthercommission deliberation. It should be notedthat some states have already develowd techni-cal standards for cable systems. rranchisingauthorities in those states should refer to suchregulations before developing their owntechnical standards.

'A guide for technical standards is developed more com-prehensively in Technical Standards and Specifications: Ordi-nance Supplement Section VII. (Washington, D.C.: Cable

9-, Television Information Center, 1973.)

2Reconsideration of Cable Television Report and Order, 36 FCC2d 359 (1972).

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In addition, the FCC does not consider itsmeasurement procedures an adequateguarantee that system performance standardswill be met. The Rules require that each systembe tested annually, and that measurements betaken at three widely separated points. In itsreport, the commission stated:

Many advised that requiring performancemeasurements at only three vaguely definedpoints would fall short of rigorously testingthe system. Consideration has been given torequiring measurements at more than threepoints in order to insure "representative"sampling of system performance. But ourview is that this requirement is not intendedto establish that each subscriber will receiveservice in accordance with the standardsthat can come only with a measurement ateach subscriber terminal. The performancecheck is, rather, assurance to the operatorand to the Commission (should the perfor-mance be questioned) that the signal pathfrom headend to check point is capable ofconforming to the standards. We are there-fore retaining the proposed requirement forthree measurement points. Many systems, asa matter of good practice, will make routineobservations at more than three points. Theultimate requirement, in any event, is thatthe technical standards must be met at eachsubscriber terminal.'

A franchising authority may wish to set forthmeasurement procedures that give reasonableassurance to local officials that standards are infact being met.

The establishment of technical standards bylocal governments is desirable for other reasons.The initial high signal quality may, over time,slowly degrade to a point where the signal qualityis not completely acceptable. Subscribers who areunhappy with the quality of service may not regarddiscontinuing service as an acceptable alternative,especially if off-air television reception in the com-munity is poor. Furthermore, cable television'spromise lies in its potential for public service; asthis service grows, the franchising authority willhave a strong interest in the technical quality ofservices provided.

The franchising authority also has an interestin seeing that cable television facilities are safelyconstructed and operated, and that the system'scomponent parts are durable and reliable. Severalfederal agencies have set forth regulations thatdeal with such issues, but no comprehensive stan-dard for safety, ruggedness and reliability in cabletelevision systems exists in one place. Therefore,

3Cable Television Report and Order, 36 FCC 2nd (1972)(emphasis supplied).

30

the franchising authority may choose to set forthmore comprehensive standards.

Finally, technical standards work no magic bythemselves. A system operator has little incentiveto adhere to a comprehensive testing program ifhis records are not examined by the franchisingauthority. In a letter to the president of a largemultiple system operator, the Chief of the FCC'sCable Television Bureau suggested the commis-sion's view of local governments' responsibilitieswith regard to technical standards.

The Commission will not, however, assumeresponsibility for enforcement of more str-ingent technical standards. Local authoritiesshould therefore be prepared to assume theburden of such enforcement.'Specifically, the center recommends a regulat-

ory program consisting of the following elements:Construction standards to insure a safe and

reliable cable systemTechnical standards for the reception of broad-

cast television signals received either off-the-airor via microwave

Technical standards for ensuring overall sys-tem performance

Procedures for testing system performance toensure that all technical standards are being met

The development of a record keeping log bookthat supports the technical standards and testingprocedure programs.

CONSTRUCTION STANDARDSAND SPECIFICATIONS

Construction specifications for cable TV systemsfocus upon two main elements: systenfsafety andsystem reliability. A cable system which isdesigned to meet very high technical and perfor-mance standards can be ineffective if the antennabreaks the first time it snows or the amplifiersshort out during the first rain.

The development of safety specifications in acable TV ordinance permits the municipality toobserve, check and.monitor and ensure systemsafety. While this aspect of the ordinance is notdirectly related to system performance and qualityof signal received, it is, nonetheless, important.The construction of a cable system involves somedegree of coordination and cooperation betweensuch various municipal departments as highways(rights of way) utilities (pole agreements),engineering (electrical standards), and federalagencies (e.g., Federal Aviation Agency for tower

'Letter from Sol Schildhause, Chief of Cable Television Bureau,Federal Communications Commission, to Edward M. Allen,August 11, 1972.

permits). As such, those standards relating to thequality of construction can be specified in the ordi-nance though it is not necessary to do so. Thefranchising authority may also want to examinelocal codes to determine whether any of themmight affect cable.

The community's interest in construction stan-dards for system reliability is based upon sub-scriber concerns that service be uninterrupted.Frequent system failure due to poor design, con-struction, or equipment should not be toleratedby the franchising authority, and can effectivelybe prevented only by monitoring construction ofthe system from the outset. Further, as publicagencies make more and more use of the cablesystem, reliability of service becomes a direct con-cern of local officials.

Construction standards generally deal withthose elements directly exposed to weather andthe elements. Thus, provisions should bedeveloped for the following:

Antennas protection against wind, ice load-ing and corrosion

System grounding proper grounding of thepower supply and metal components of the sys-tem to ensure that the system is protected againstlightning, power surges, and electrical interfer-ence

Arial cable plant provision to ensure thatthe cable is properly supported, that electronicsare weatherproofed and protected from cor-rosion, and that equipment is accessible formaintenance

Underground cable plant provision to ensurethat conduit is rugged and large enough to permitadding cable in the future when it is needed. Provi-sions to protect cable under heavily traveled road-

The substance of reliability and safety standardsshould be a comprehensive collection of relevantprovisions from the National Bureau of Standards,the Federal Aviation Agency, state regulations, andlocal provision for the use of the community'sstreets.

Compliance for construction centers mainly onthe monitoring of the system as it is built. There-after, the franchising authority's role diminishes.

STANDARDS FOR RECEPTION OFBROADCAST TELEVISION SIGNALSOFF-THE-AIR OR VIA MICROWAVE

Cable television systems may meet very highperformance standards yet still deliver low qualitypictures to subscribers. Broadcast television sign-als carried on the cable may be poor because the

headend antenna is badly situated, poorlydesigned, badly installed, or because the televi-sion station broadcasting the signal is defective.

From the subscriber's viewpoint, poor serviceis poor service, regardless of the cause. Thefranchising authority, however, must be able topinpoint responsibility for poor performance.Standards for reception of broadcast signalsdefine for a system operator the minimum qualityof the signal the system must secure with itsantenna before it distributes the signal to sub-scribers. These standards also provide a way ofgrading the quality of each off-the-air signalreceived, against which the performance of thesystem in delivering that signal to subscribers canbe measured.

The first stop in defining specific standards forsignal acquisition in a community is to requirethat a signal survey be conducted. This surveycan be performed either by the municipality orby the system operator. In either case, it is doneto determine what television signals can bereceived, what quality of pictures to expect andwhat possibilities there are for the headendthe desired site location, height of tower, antennaarray designs and sources of interference.

Armed with results of a signal survey, thefranchising authority is in a position to requirethe system operator to place his antennas anddesign them to receive the best quality of signalpossible, given the character of local geography.

OVERALL SYSTEM PERFORMANCE

The FCC has set technical standards only forthe delivery of broadcast television signals by acable system. The commission expects soon todevelop standards for cablecast programs, andultimately, two-way communications.

In the meantime, effective performance stan-dards for broadcast television signal carriage isthe most appropriate means for assuring that thecable system is capable of doing what it is designedto do.

One way of defining performance standards isto specify exactly how each component of thecable system will perform, and to require the sys-tem operator to install the specified equipment.This is an unsatisfactory approach because it doesnot guarantee the overall performance of thesystem.

A more effective approach is to require the sys-tem to deliver a specified quality of signal to sub-scribers, without specifying how it should do so.The franchising authority can require that for agiven grade of signal received at the cable system

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headend, the system must deliver a specific stan-dard of signal quality to subscribers. Since stan-dards for the acquisition of broadcast signals havealready been defined, ordinance provisions forsignal delivery standards should be developed tocomplete performance standards.

PROCEDURES FOR TESTING THE SYSTEMTO ENSURE THAT STANDARDS ARE MET

No standard has meaning unless procedures aredeveloped for its enforcement. The franchisingauthority should set forth reasonable and effectiveprocedures to test the ability of the cable systemto meet prescribed technical standards. Theseprocedures should be built around three kindsof tests.

First, as a condition of the franchisingagreement, the franchising authority mightrequire an initial, exhaustive, proof of perfor-mance prior to the provision of service. The maintrunks should be tested without exception, andparts of the feeder network selected at random.Finally, a representative number of subscriber tapsshould be tested. The locations might be as fol-lows:

At the last trunk amplifier in widely separatedpoints in the system

At the last line extender in widely separatedfeeders of the system (feeders not fed by the trunktested above)- At multitap locations as selected at random toprovided coverage of the entire area.

The purpose of the test in each case would beto build for the franchising authority a statisticallysound "portrait" of the system's capability. Initialtesting should occur with the completion of con-struction of each section of the system and shouldbe tied to the construction timetable establishedby the franchising authority.

Many performance tests involve an interruptionof service. Once service has begun, tests whichinterrupt service should be conducted only asoften as is necessary to ensure that performancestandards are maintained. A second kind of testshould take place once a year when the franchisingauthority should require the system operator toensure that the system complies with both FCCand local performance standards.

Finally, the franchising authority could requirea series of monthly, inexpensive tests that do notrequire the disabling of the system. Initial andannual tests can be prepared for, by judicious"tuning" of the system. An effective monthly test-ing program should result in high quality systemperformance all the time. Monthly tests, con-

32

ducted by the system operator and reported tothe franchising authority, provide a mechanismto ensure that the system operates near its ratedcapability.

RECORDS TO BE KEPT

The system operator should permanently main-tain detailed records which show exactly how thesystem was constructed, in order to facilitate themodernization or overhaul of the system in thefuture.

Initial and annual proof of performance testsshould be evaluated by a competent engineer,preferably someone not involved with the systemoperator. Monthly tests should be examined byan agent of the franchising authority, but they arelikely to be simple enough to be interpreted bya layman, with assistance from the systemoperator.

Finally, the system operator should be requiredto keep a record of his responses to subscribercomplaints, including tests made of what waswrong and proof that the problem was satisfactor-ily resolved.

Technical standards work no magic by them-selves. A system operator has little incentive toadhere to a comprehensive testing program if hisrecords are not examined by the franchisingauthority.

C. Role in the Evolution ofCable Technology

Local officials planning for cable should keepin mind that they are dealing with a rapidlydeveloping technology. A system that is well-designed and meets high technical performancestandards for today can become out-of-datetomorrow if the community does not provideadequate safeguards to ensure that the system canevolve along with technology. System designshould be such as to minimize obsolescence, andsystem operators should be encouraged to experi-ment with new technological innovations.

There are two essential ingredients to thisprocess. First, the franchising authority shoulddevelop the capacity to monitor independentlytechnological developments in cable communica-tions. No procedural mechanism will protect theinterests of the community. unless it is activatedby intelligent monitoring efforts by a specificagency in the local government.

Second, there must be a procedure which givesthe franchising authority the power to negotiate

with the system operator for installation in thesystem of new technical capabilities.

In order to monitor state-of-the-art develop-ments, many communities have formed citizenadvisory commissions. The commissions are com-prised of civic, technical and municipal leaderswho periodically meet with the cable system man-agement and interested citizen groups toexchange ideas and provide feedback to locallegislative and administrative officials.

The example below from New York City illus-trates a similar approach. It provides a proceduralbasis for making changes that consider both theconsumer and the system operator. A cable com-mission might perform the same function as NewYork's Director of Franchises. The requiredchanges may involve heavy expenditures, so thatthose responsible for technical review must notonly be familiar with the development of thetechnology but also its usefulness to the com-munity, and the costs involved.

After consultation with the Director ofCommunications, if the Director ofFranchises determines, giving due regard totechnological limitations, that any part or allof the System should be improved orupgraded (including, without limitation, theincreasing of channel capacity, the furnishingof improved converters, and the institutionof two-way transmission), he may order suchimprovement or upgrading of the System, tobe effected by the Company within a reason-able time thereafter. If the Company disputesany such determination or the reasonabletime within which it is to be implemented,it may, within twenty (20) days after theissuance of such order, demand that the mat-ter be arbitrated pursuant to Section 20 ofthis contract.

Section 20. ArbitrationMatters which are expressly made arbi-

trable under provisions of this contract shallbe determined by a panel of three arbitratorsappointed by the Presiding Justice of theAppellate Division of the Supreme Court ofthe State of New York for the First JudicialDepartment. The fees of the arbitrators shallbe fixed by said Presiding Justice. Theexpenses of the arbitration, including thefees of the arbitrators, shall be borne by theparties in such a manner as the arbitratorsprovide in their award, but in no event willthe City be obligated for more than half theexpenses. The determination of a majorityof the arbitrators shall be binding on theparties. In the event that an arbitrable matter

arises contemporaneously under anotherfranchise, involving the same issue as thatto be arbitrated under this franchise,. theCompany will not claim or assert that it isprejudiced by or otherwise seek to preventor hinder, the presentation of the arbitrablematter under such other franchise for deter-mination by a single panel.

III. CONCLUSION

In the future, cable must find markets for thenew services that can be provided by current cabletechnology and for those services that the emerg-ing two-way cable technology will soon be capableof providing. Markets must be found in an arenaof competing telecommunications technologiessuch as telephone, broadcast television, radio,and specialized common carriers.

Nonetheless, there is little doubt that an impor-tant role will develop for cable no matter whatthe ultimate configuration of urban telecommuni-cations. More importantly, local officials cannotwait until the future is clear. Franchising decisionswhich will establish the frame of reference forcable television development are being madenow.

It is probably not too much of an exaggerationto state that the public promise of cable televisiondepends more upon the quality of franchisingdecisions than upon any. other single factor. Anunderstanding of the fundamentals of cable televi-sion technology and its implications on design,technical performance, and future developments,is vital to the quality of local decisions.

Technological decisions are difficult to makebecause they are complex and not easily under-stood; but, more fundamentally, because they are

33

essentially efforts to both define and chart thefuture.

Cable television technology is no exception.Such abstract terms as "attenuation," "frequencyresponse," "second order distortion," and othersdo not inspire confidence in the minds of thosewho must make decisions without the benefit ofan engineering degree. Those terms evoke a fee-ling on the part of public officials that only techni-cally trained experts can make technological deci-sions.

The reverse, however, may more often be thetruth. Technological decisions are seldom purelytechnical rather, they concern our values, ourworld view, our sense of the kind of society wewish to build. Decisions of this kind should bemade by responsible officials, not by technicians.

This may be particularly true in the case of cabletelevision. Imbedded in seemingly technical deci-sions about dual or single cable, converters orswitches, trunks, feeders, or drop lines, is theform of a new communications medium whichmay affect in important ways the manner in whichwe lead our lives.

This report does not lighten the responsibilityof decision making, nor does it make the decisioneasier. What it does, hopefully, is explain theaspects of cable technology with which decisionmakers should be familiar, point up the principalquestions decision makers must confront, andstate alternative responses to these issues so thatthe opportunity for decision will not be lost.

In the final analysis, we all must realize thattechnology drives us back to ourselves. It offerswide choices for good or for bad. It expandsour capacities but with effects we can nevercompletely comprehend. We must be as analyticalas we can be in making such choices; but in thelong run our best guide to technological decisionsmay be carefully considered human values.