THE PICTURE OF THE FUTUREThe Bell System is about to add PICTURE-

PHONE® service to the many services it now of-fers customers. A major trial of a Picturephonesystem is presently under way, and commercial

service is scheduled for mid 1970. Because Pic-turephone service is a large undertaking that willhave a profound effect on communications, theRECORD is pleased to be able to present this specialissue describing the new system for our readers.

Special issues have become an important partof the RECORD's continuing story of science andtechnology at Bell Labs. The first one, in June1958, dealt with the transistor and marked thetenth anniversary of its invention at Bell Labs.Since then there have been special issues on theTELSTAR® project, No. 1 Ess, and integrated elec-tronics. In addition, there have been single-topicissues devoted to the N-3 and L-4 carrier trans-mission systems. We hope to continue to presentsuch special issues from time to time as a way ofhighlighting subjects of special importance.

PAGE

Contents

134

PICTUREPHONE Service-A New Way of CommunicatingAn introduction by Julius P. Molnar, Executive Vice President, Bell TelephoneLaboratories.

136

PICTUREPHONE

Irwin DorrosA broad view of the PICTUREPHONE system sets the stage for the more detaileddiscussions that f ollow.

142

Getting the Picture

C. G. DavisThe acceptance of PICTUREPHONE service depends largely on the equipment thatpeople will see and use-the PICTUREPHONE set itself.

148

Video Service for Business

J. R. Harris and R. D. WilliamsA look at how PICTUREPHONE service will be added to existing business telephonesystems.

154

Choosing the Route

F. A. Korn and A. E. RitchieA proven Bell System performer, No. 5 crossbar, will be the nucleus for switchinga brand-new communications service.

160

The Evolution of PICTUREPHONE ServicePhotos highlighting some important dates and events that have led up to thesystem described in this issue.

162

Transmission Across Town or Across the CountryD. W. Nast and I. Welber

Digital transmission is the key to plans for transmitting high-quality PICTURE-PHONE signals over almost unlimited distances.

169

Connecting the Customer

F. T. Andrews, Jr., and H. Z. HardawayThe continually-evolving customer loop plant is adding a new capability to its com-munications repertoire-video transmission.

174

Devices-The Hardware of Progress

S. O. EkstrandPICTUREPHONE service would not be possible without the electronic devices thatmodern technology has produced.

181

Maintenance-Keeping the System in Trim

A. E. SpencerA description of some of the equipment and procedures that will be used to main-tain the PICTUREPHONE system.

186 TomorrowSome of the things Bell Labs is doing now to make the PICTUREPHONE system aneven better, more versatile instrument for human communication.

188

The Authors

Picturephone Service-A New Way of Communicating

An Introduction by Julius P. Molnar, Executive Vice President, Bell Telephone Laboratories

Rarely does an individual or an organization have an opportunity to createsomething of broad utility that will enrich the daily lives of everybody.Alexander Graham Bell with his invention of the telephone in 1876, and thevarious people who subsequently developed it for general use, perceived suchan opportunity and exploited it for the great benefit of society. Today therestands before us an opportunity of equal magnitude- PICTUREPHONE® service.

FIFTY YEARS AGO people communicatedover distances mainly by letters and tele-grams, and used streetcars, railroads, andships for travel to see each other. Graduallytelephone usage increased until it is today themost common means of communication, andthe automobile and jet airplane now providemost of the transportation we use to get to-gether for face-to-face conversation. I predictthat before the turn of the century Picture-phone will similarly displace today's means ofcommunication, and in addition will makemany of today's trips unnecessary.

The urge to travel and see the world withone's own eyes will probably be enhanced,not lessened, by the availability of instant,personal picture communications; but theneed for many ordinary trips for shopping,for conducting normal business, and for somesocial purposes should be greatly reduced. Asa result, there will be less need for dense pop-ulation centers. We can even hope to see anend to the continuing increase in city trafficand traffic jams.

Picturephone is therefore much more thanjust another means of communication. It mayin fact help solve many social problems,particularly those pertaining to life in the bigcity. Bringing Picturephone into general useI see as one of the most exciting opportunitiesfor the wise use of modern technology.

Most people when first confronted with Pic-turephone seem to imagine that they will useit mainly to display objects or written matter,or they are very much concerned with howthey will appear on the screen of the calledparty. These reactions are only natural, butthey also indicate how difficult it is to predictthe way people will respond to something newand different.

Those of us who have had the good fortuneto use Picturephone regularly in our dailycommunications find that although it is use-ful for displaying objects or written matter,its chief value is the face-to-face mode of com-munication it makes possible. Once the noveltywears off and one can use Picturephone with-

May/June 1969

out being self-conscious, he senses in his con-versation an enhanced feeling of proximityand intimacy with the other party. The uncon-scious response that party makes to a remarkby breaking into a smile, or by dropping hisjaw, or by not responding at all, adds a defi-nite though indescribable "extra" to the com-munication process. Regular users of Picture-phone over the network between BTL andAT&T's headquarters building have agreedthat conversations over Picturephone conveymuch important information over and abovethat carried by the voice alone. Clearly, "thenext best thing to being there" is going to bea Picturephone call.

Real person-to-person conversation is stillman's most complete and satisfying way ofcommunicating. Letters and other writtenforms of expression have their values, butthey suffer from two disadvantages. They areessentially one-way communications, and withwritten words it is difficult to convey mean-ings beyond their strict lexical definitions.The telephone overcomes one of these dis-advantages because it permits a two-way,give-and-take interchange of information andideas. It partially overcomes the second dis-advantage also, because in addition to theliteral meanings of words, one can-withvoice tone, volume and inflection-conveymany of the additional elements of a completecommunication.

For the final, visual elements of two-waycommunication, we have had to rely on visits,meetings, and conferences. Even here thereis a disadvantage, however. Such communi-cation is at its best only when the participantsare within about ten feet of each other. Be-yond this distance, face-to-face communica-tion quickly becomes unsatisfactory. Just asthe telegraph overcame this distance barrierfor written words, and the telephone forspoken words, so Picturephone service willbring people face-to-face across our contin-ent and eventually over oceans.( For concluding remarks and a look into thefuture of Picturephone service, see p. 186.)

135

THE TELEPHONE brought a new dimension to hu-man communications. Where previously men

had been able to send written messages over wiresas electrical signals, the telephone made it pos-sible for the human voice to span the miles. Now,almost a hundred years later, the telephone iscommonplace and another dimension is beingadded-that of sight. And just as the telephonehas revolutionized human habits of communicat-ing and made a major contribution to the qualityof modern life, many of us at Bell Labs believethat PICTUREPHONE® service, the service that letspeople see as well as hear each other, offerspotential benefits to mankind of the same magni-tude. It is a tribute to the flexibility and versatilityof the existing telephone network that Picture-phone service, now being readied for introductionas a regular Bell System offering, can be addedas an integral part of telephone service.

What is Picturephone service like? Most im-portant, of course, the user sees the person withwhom he is talking. People today are so accus-tomed to using the telephone and to its usefulnessas an instrument of communication, that theysometimes overlook the importance of vision incommunication. But think, do you telephone theperson in the next office or go to see him? Mostpeople sense a more complete and satisfying ex-change when they can both see and talk to eachother. Thus, the advantage of more complete com-munication with Picturephone service is readilyapparent.

Picturephone service is useful in other waystoo. Graphic material, such as drawings, photo-graphs, and physical objects, can be viewed withthe Picturephone set. The equipment can also beused to communicate with a computer. The cus-tomer "talks" to the computer via TOUCH-TONE@dialing buttons, and the computer's responses aredisplayed on the picture tube (see PicturephoneSets Put a Computer on Executive Desks, REC-ORD, June 1968).

When Picturephone service becomes availablecommercially (in the early 1970's), it will prob-ably be accepted most readily by businesses-par-ticularly by large corporations. The executives ofa corporation with offices in different locationsform a natural "community" with a need for theutmost in communication facilities. Trials alreadyconducted and now in progress have demonstratedthe usefulness of Picturephone service in thecorporate environment (see The Evolution of Pic-turephone Service, RECORD, October 1968). AsPicturephone service becomes widely availableand a public awareness of it develops, it willspread gradually into the residential market.

138

The equipment at the Picturephone custom-er's location consists of four parts: a 12-buttonTouch-Tone telephone; a display unit, with pic-ture tube, camera tube, and a loudspeaker builtin; a control unit, which contains a microphone;and a service unit containing power supply, logiccircuits, and transmission equalizing circuits,which is installed out of sight.

Picture standards have been chosen for the bestpossible picture, subject to the limits imposed bycost and transmission capabilities (see the table onpage 139). The picture signal is composed ofabout 250 active lines, displayed 30 times per sec-ond on a 5.5 -inch by 5-inch screen. Resolution isthe same in the vertical and horizontal directions.The quality of the picture equals that of a typicaltelevision set in the home. Transmitting the pic-ture signal requires a 1-MHz bandwidth.

Normally, a person using the Picturephone setwill be about 36 inches away from the screen. Thefield of view at that distance is adjustable from17.5-by-16 inches to 28.5 -by-26 inches. Thisrange of sizes is designed to give the user free-dom to move from side to side during his conver-sation, and to permit one or two other persons tobe "on camera" at the same time. The camera irisautomatically adjusts the lens for changes inroom lighting.

The Picturephone system is designed to takemaximum advantage of the existing telephonenetwork and add as little new equipment as pos-sible. Picturephone customers will make voice-only telephone calls from their regular telephones,with all extra features, such as speakerphone,card dialers, and key telephone options, in place.

A 12-button Touch-Tone telephone set will berequired for Picturephone service (all Touch-Tone phones are now being manufactured with 12buttons). The Picturephone customer initiatesa video call by pressing the lower right-hand, or12th button, labeled #, and then, in most cases,dials the regular telephone number of the personhe is calling.

A distinctive ring, created by a new toneringer, identifies an incoming Picturephone call.In key telephones, such as a six-button set, thekey corresponding to the called line lights red toidentify a Picturephone call; the key lightswhite to identify a voice-only telephone call.

Lines equipped for Picturephone service canalso have voice-only extensions-a secretary'spickup, for example. Video calls can be answeredon such extensions; the caller sees a blank screenuntil the call is answered on a Picturephone set.An attendant at a PBX, for example, may or maynot be equipped for picture service, as the cus-

Bell Laboratories Record

tomer wishes. In addition, at the customer's op-tion a fixed image, such as a company trademark,can be transmitted to the caller while the atten-dant handles the call.

Communication services available to the busi-ness community today range from simple directlines to PBX and centrex arrangements for busi-ness customers. Individual service features in-clude dial intercommunication, attendant service,and, in the case of centrex, direct inward dialingto telephones and identified outward dialing, aswell as a variety of sophisticated services tailoredto meet specific needs.

Picturephone service will be a valuable addi-tion to the telephone services already available tobusiness. To assure continuation of these services,new Picturephone key telephone units offeringpickup, hold, and intercom service will be fur-nished. Customers served by the 701 and 757PBX's, the No. 101 ESS, and the No. 5 crossbarcentrex-CO (switched in the central office) sys-tems will be able to add Picturephone serviceand retain all of their major PBX and centrex fea-tures. Picturephone service with the No. 1 Esscentrex-CO system and other new PBX systemswill be introduced later.

Thus far, our discussion has related primarilyto Picturephone service as it will affect the user.What about the rest of the system? Here too thephilosophy of taking maximum advantage of ex-isting telephone facilities prevails. The upperdiagram on page 140 shows the basic local equip-ment arrangement.

Picturephone service requires no modificationsto existing two-wire loops (the wires that con-nect a customer's telephone to the local switchingoffice) ; voice-only calls and the voice portion ofPicturephone calls use these wires. Two morepairs of wires in standard telephone cables areassigned for the picture signals, one pair fortransmission in each direction. Equalizers are in-serted at about one-mile intervals along the addi-tional pairs. The ON-OFF switch-hook signals andTouch-Tone dialing signals, as well as the voiceportion of Picturephone calls, are transmittedover the voice pair.

At the local central office, the voice pair is con-nected to the existing telephone switch in theconventional way. The video pairs, however, areconnected to a separate four-wire video switchunder the control of the existing telephone switch-ing machine.

As Picturephone service is first offered, No. 5crossbar switching machines will be modified toswitch video calls; the capability will be addedto No. 1 ESS later. Picturephone service for cus-

tomers served from step-by-step, panel, or No. 1crossbar offices will be routed to a nearby No. 5crossbar or, later, a No. 1 ESS office.

Whenever a customer dials a call, the commoncontrol equipment in the switching machine recog-nizes the digits and causes a talking path to beestablished. For voice-only calls, the existing two-wire telephone switch will make the connection.When the special prefix, #, is dialed, indicating aPicturephone call, the talking path is establishedby the two-wire telephone switch, and a path isestablished simultaneously by the four-wire videoswitch to the trunk side of the switching machine.There, the audio and video paths form a compos-ite six-wire appearance. For intra-office calls, thesix-wire Picturephone signal returns through theswitches to another line. For calls to a distant cen-tral office, however, the path is established over asix-wire Picturephone trunk. The audio portionof the six-wire trunk is never used for voice-onlytelephone traffic.

The Picturephone signal discussed thus faris a line-by-line electrical representation of thescanned shades of gray,in the picture material.Short synchronizing pulses, between scan linesand fields, tell the receivers how to line up the partsof images. This kind of signal is called "analog."Between central offices, up to about six milesapart, the picture signal is transmitted over the

May/June 1969 1 39

The customer's Picturephone set is connected to the local cen-tral office over a six-wire loop. As in today's telephone service,one pair of wires carries the voice signal. Two other pairs withequalizers are used for the two directions of video transmission.The audio pair is switched in the central office in the conven-tional way, while the video portion is switched by a newly de-signed four-wire video switch controlled by the switching ma-chine. The entire Picturephone signal is switched to othercentral offices over a special six-wire trunk; voice-only callscontinue to be switched over conventional two-wire trunks.

The Picturephone signal is transmitted between nearby cen-tral offices (less than six miles) in analog form (top). Fortransmission beyond six miles, the picture signal and the audioand signaling information are digitally encoded into a com-posite 6.3-Mb/ s signal and decoded again at the distant office.

Picturephone trunk in analog form. The Picture-phone trunk in this case consists of three separatewire pairs in exchange cables, with equalizersplaced at about one-mile spacing in the two videopairs, as in loops.

For transmission beyond six miles, the picture,voice, and interoffice signal information is digitallyencoded into a composite pulse stream of 6.3 meg-abits per second (Mb/s). This is called a "digital"

signal. Once encoded, a signal usually is not de-coded until it is within six miles of the distantlocal central office. Limitation to a single encodingin a connection is required to prevent an accum-ulation of the picture degradation that occurseach time the signal is coded and decoded. Whilesome impairment is caused by the single codingand decoding, digital transmission is highly de-sirable because virtually no further impairmentoccurs during the transmission of the digitalpulse streams.

Picturephone signals remain in digital formfor switching in toll offices. No. 5 crossbar switch-ing offices will be the first to perform the tollswitching function. Later electronic toll centersnow being planned will switch Picturephone calls.

The application of analog and digital transmis-sion is shown below left. The T-2 digital carriersystem, expected to be introduced in the near fu-ture, transmits at 6.3 Mb/s and is, in fact, thereason for selecting this particular signal encod-ing rate for Picturephone signals. The T-2 systemoperates over wire pairs for distances up to sev-eral hundred miles.

Digital transmission systems now being de-veloped will ultimately take over the long-haultransmission of Picturephone signals. Until then,two existing facilities will be used: the TD-2 mi-crowave radio relay system and the L-4 carriersystem. In TD-2, a 20-Mb/s pulse stream, carry-ing three coded Picturephone signals, is trans-mitted on a single radio channel. In the L-4system, a 13-Mb/s pulse stream, carrying twocoded Picturephone signals, is transmitted inplace of one of the six mastergroups on a coaxialtube. No additional transmission facilities, otherthan the designs now existing or contemplated forregular telephone service, will be necessary totransmit Picturephone signals. A single trans-mission network will transmit all services.

The picture that is finally viewed at a Picture-phone receiver contains impairments introducedby each part of the built-up connection. Just as intoday's telephone network, the end-to-end impair-ments are controlled by holding each part of theconnection within specified limits. Based on an-alytical calculations and subjective tests, each ofthese has been assigned a numerical end-to-endmaximum value with a specified limit allocatedto stations, loops, trunks, etc. Dealing with theseimpairments requires techniques that are, in manycases, different from those used for audio trans-mission systems. The necessary new techniquesare being developed.

The switched network arrangements for Pic-turephone service will be useful for services in

1 40 Bell Laboratories Record

addition to Picturephone calling. Equipment willbe developed that, to the network, looks like a Pic-turephone set, but is actually a data set. A cus-tomer will be able to dial the data set, usinga regular Picturephone number, and reach a com-puter. The Touch-Tone dial will then be the meansof communicating with the computer to retrievedata or interact in a computation. (One kind ofcomputer response is shown in the upper photo-graph on this page.)

The network will also be equipped to handlemachine-to-machine data traffic at a rate of aboutone Mb/s, much as DATA-PHONE® service handlesvoice-band data. Such service will require an ap-propriate data set at each end of a connection.

To verify the practicality of the Picturephonesystem plan, to make refinements in it, and to testcustomer acceptance of the features, a producttrial was begun in February of this year and isstill in progress. A total of 41 sets have beenplaced in offices of the Westinghouse ElectricCorporation in Pittsburgh and New York with tolllinks between cities. Each set can be dialed fromany other set, and computer access facilities areincluded in this trial. Acceptance by the usershas been enthusiastic.

Many readers will be led to speculate aboutpossibilities for future improvements. Among theitems currently receiving attention are higherresolution for transmitting detailed documents,color, capability for making conferences calls, andreducing the transmission band by taking advan-tage of inherent redundancy in video images.

Satisfactory transmission of a stationary im-age, such as a drawing resting on a table, doesnot require 30 frames per second. In theory an im-age may be slowly scanned a few times per sec-ond with many lines, resulting in higher-resolutiontransmission within the same 1-MHz channel.Optional equipment arrangements to achieve thisare now being investigated.

A sizable fundamental research effort is nowin progress to gain enough understanding to pro-pose a compatible color system for future phasesof the service.

For Picturephone conference calling, an ex-periment is now in progress in which a voice-actuated switch causes the picture of the persontalking to appear on the screens of all other con-ferees. Finally, a number of signal-processingapproaches which may reduce the 6.3-Mb/s rateof transmission are in the research stages.

A practical beginning has been made. Develop-ment of Picturephone service to its present stagebrings the goal of better, more natural, and morenearly complete communications nearer to reality.

Besides the "see-as-you-talk" capability of the Picturephoneset, man can communicate with a computer as well. A data set,which appears to the switched network as a regular Picture-phone set, permits the set to be connected to a commercialcomputer. In this case, the Touch-Tone dial is used to communi-cate with the computer and the information retrieved or theresults of a computation can be displayed on the Picturephonescreen. The variety of characters available to display informa-tion on the Picturephone screen is shown in the bottom photo.

May/June 1969

The greatest technical accomplishment in the world may go unused if it is not designedwith people in mind. Thus, the parts of the Picturephone system that people will usedirectly have been designed to be attractive, easy to operate, reliable, and versatile.

Getting the Picture

C. G. Davis

EOPLE'S REACTIONS to PICTUREPHONE® servicewill be based largely on the unit that displays

the picture, along with accompanying controlsand other items in the customer's home or office.Is the equipment attractive? Functional? Reli-able? Is it easy to use? Is the picture good? Com-ing up with the right answers to these and sim-ilar questions has been a major concern at BellLabs as the Picturephone system has evolved.

The "right answers" means, first of all, that thepicture itself must be clear and sharp and muststay that way without a lot of tuning adjust-ments. The equipment must be easy to operate. Thecamera must adapt readily to a variety of picturesubjects, backgrounds, and lighting conditions.At the same time, the set must be versatileenough to meet diverse needs such as showingsketches or objects, changing the field of view,or allowing the person using it to turn off thecamera if he doesn't want to be seen. The usershould be able to select any of these modes easilyand conveniently, with little need for thought orchance of error. Finally, the set, like all Bell Sys-tem equipment, must be designed for a long lifeof trouble-free service under the hazards ofeveryday use.

These objectives, and the knowledge gainedfrom study and experimentation over the past 10years (see The Evolution of Picturephone Ser-vice, RECORD, October 1968), have helped shapetechnical possibilities and customer preferences

May/June 1969

into a successful Picturephone system. In 1965,a significant milestone in the evolution of Pic-turephone service was the beginning of producttrials, using what was called the "Mod I" Pic-turephone set. The results of these trials werethen used to develop the latest and completelynew Picturephone set, known as the Mod II.

The Mod II set consists of a picture displayunit (containing the camera, picture tube, andloudspeaker), a control unit (containing the con-trol buttons and knobs and a microphone), a 12-button TOUCH-TONE® telephone, and a serviceunit (containing the power supply, logic circuits,and transmission equalizing circuits). The firstthree units are color-coordinated and intended tofit in as harmoniously as possible with any decor,since they will almost always be in plain sight.The service unit is intended to be installed out ofsight and can be up to 85 feet away from theother three.

The display unit is mounted on a sculpturedring stand and can be turned almost all the wayaround (340 degrees)on the stand. Sincethe ring stand hasa "non-skid" base,the unit is not eas-ily pushed or pulledoff the surface onwhich it rests. How-ever, when the unit

is tilted close to the point of tipping over, the non-skid material, which covers only part of the base,lifts away from the surface and the unit slidesinstead of falling on its side. All of the video cir-cuits, the camera and picture tubes, and thespeaker are in the display unit. The area aroundthe face of the picture tube has a mat black finish,which is ringed by a band of chrome that servesas a transition to any of the many available shellcolors.

The picture tube face, which is 5 by 5.5 inches,displays a picture constructed in the same wayas that on a home TV set. That is, it displays 30frames a second using odd-even line interlace togive 60 fields a second, thereby yielding an ac-ceptable "flicker" rate. A complete frame con-sists of about 250 visible interlaced lines, andhorizontal and vertical resolution are essentiallyequal.

A near-perfect interlaced picture is providedin the camera by an integrated digital synchro-nizing generator, which is probably the most un-usual circuit in the station set (see Devices-The Hardware of Progress, in this issue). The

The customer service unit contains the low-voltage power supply, the control circuits, and thestation set equalizer, where required. The unit isusually not in view at an office or home, and canbe placed up to 85 feet away from the other units.

synchronizing generator promises to yield sig-nificant cost savings in the production version ofthe Picturephone set.

Beyond the quality of the picture itself, otherfactors played an important part in the design ofthe display unit. For example, the camera isplaced above the picture tube to make the eyecontact angle as small as possible. This is signif-icant because, while the camera is looking at thesubject, the subject is looking at the picture tube.The apparent "looking away" is annoying to theviewer unless the angle is small. The least an-noyance occurs when the subject appears to belooking slightly down, which is frequently thecase in normal conversation. Locating the camerajust above the picture tube creates this effect.

The best position for the camera has proved tobe about 12 inches above the desk top so that itsfield of view is essentially straight ahead. Herethe camera gets the most natural-looking, leastdistorted view of the subject, keeping him oncamera while allowing some movement, and (hope-fully) not picking up too many ceiling lights.

The lens in the camera has an aperture of f/2.8,with a viewing angle of about 53 degrees. It isnormally focused for a distance of about 3 feetfrom the set. This distance can easily be changed,however, by moving the button above the lens tothe left or "20" position, changing the focal dis-tance to a field centered about 20 feet from theset.

An automatic iris adjusts the lens opening forambient lighting conditions. The iris is of aunique friction-free design, and is controlled bypeak averaging of the video signal. Omitted fromthese measurements, however, are the upper andlower quarters of the picture, where ceiling lightsand white shirts could unduly influence the cam-era setting. When the iris has opened completely(at a scene brightness of about 12 foot-lamberts)an automatic gain control circuit in the cameraamplifier takes over control of the signal level, al-though with increasing noise as the light level de-creases. In good light, with a small opening of theiris, the camera has an increased depth of field.This effect is exactly the same as with an ordin-ary photographic camera, where a large "f" num-ber allows both near and far objects to be insharp focus.

In addition to the camera, the display unit alsocontains a loudspeaker. Since the voice comingthrough the speaker is normally that of the per-son in the picture, it is appropriate that the loud-speaker be located as close as possible to the pic-ture. However, since the loudness of the voiceis best controlled by the listener, the "VOLUME"

144 Bell Laboratories Record

control knob is located on the separate controlunit, which is normally at his fingertips.

The "ON" button, of course, turns the set on.But, during a conversation, if the viewer desiresto mute his microphone, he again presses andholds the "ON" button. This allows him to talkto someone else in the room without being heardby the person at the other end of the line. To re-sume conversation over his Picturephone set, hesimply releases the button.

Although the user will normally stay reason-ably centered on camera without giving the mat-ter any attention, he can check his position bypressing the "MONITOR" button on the controlunit and viewing his own picture. Pressing the"MONITOR" button a second time returns the pic-ture of the person at the other end of the line. Ifat any time the user does not want to be seen (afrequent concern of housewives), he (or she) canpress the "DISABLE" button and a distinctive barpattern will be substituted for the picture. Aswith the "MONITOR" button, pressing the "DIS-ABLE" button a second time returns the picture.

"SIZE" and "HEIGHT" controls are real contri-butions to the versatility of the Picturephoneset. They permit the user to "zoom" his camera,changing the field of view by more than 2 to 1 inarea, and to adjust the effective height at whichthe camera is pointed. Both functions are con-trolled from the control unit, without involvingany mechanical movement of lenses or camera as-sembly. The adjustments are made possible bythe silicon target in the camera, because the sili-con target doesn't "burn-in" a memory of the areascanned by the electron beam.

The image on the camera target is always thatof a field 26 inches high by 28.6 inches wideabout 3 feet in front of the set. When the sizecontrol is turned to its upper extreme, the entiretarget is scanned, giving a "wide-angle" field ofview. When the size control is set at the lowerextreme, only a portion of the target, correspond-ing to a field 16 inches by 17.6 inches at the 3-foot distance, is scanned. While this narrow-angle field is considered the normal position, res-olution may be traded for greater field of vieweither to allow the user to move around more infront of the camera or to accommodate morethan one person on camera (see A "Solid-State"

Using the SIZE and HEIGHT controls on the con-trol unit, a person making a Picturephone callcan adjust his (or her) own image without mov-ing the display unit itself. The HEIGHT controlmoves the image up (top, at right) or down. TheSIZE control moves the image away, in effect, orbrings it closer, electronically. A camera irisautomatically adjusts the lens aperture to com-pensate for any differences in light intensity.

Electron Tube for the Picturephone Set, REC-

ORD, June 1967).For any setting less than the widest angle, the

user can, by adjusting the HEIGHT control, movethe reduced raster to scan the top or bottom por-tions of the image. Although a mechanical tilt ad-justment allows an installer to compensate fordesk and chair heights, the user can later adjustthe set for his own height by using the electronicheight control.

While Picturephone service is intended pri-marily for face-to-face conversation, visual com-munication sometimes entails showing drawings,documents, or other physical objects. This can beawkward if the customer has to hold things up infront of the camera. Therefore, the set is de-signed so the user can point the camera down atthe surface on which the set rests and still keepthe picture tube in view. This is done with a mir-ror swivel-mounted in the display unit. It can bebrought in front of the camera by moving thebutton above the camera lens to the "1" position.The field of view of the camera when the mirroris out is 5 inches by 5.5 inches, with the top ofthe field at the edge of the ring stand. Movingthe mirror into position also shortens the focaldistance of the lens to one foot, reverses the cam-era sweep to correct for the mirror image, andlocks the camera in the narrow-angle mode. Theresolution at this distance is adequate for simplesketches, photographs, and the like. Typed text isof marginal legibility, and the 5x5.5-inch fielddoes not, of course, encompass an 8.5x11-inchtyped page.

Inside the plastic shell of the display unit, aheat shield at the front of the camera and a cop-per heat sink keep the camera from getting toohot. Both the shield and the heat sink are neces-sary since the right place for the camera from ahuman-factors standpoint turns out to be theworst possible place from a heat standpoint. Analuminum heat sink at the rear of the displayunit holds the power transistors for the sweepdrives and the power supply for the cathode-ray

Picturephone display units being assembled andtested at Western Electric's Indianapolis plant.Among the many operations: mounting the pic-ture tube and frame assembly on the ring stand(top left), checking circuit boards visually (topright), placing them in the display unit (bottomleft), and finally, testing for picture alignment.

May/June 1969

heater. Top and bottom vents at the rear of theshell provide chimney action for cooling this heatsink.

The high-voltage power supply is encapsulateddirectly in front of the aluminum heat sink.When the shell is removed, an interlock at therear of the unit disables the high-voltage powersupply. A strategically placed shield on the re-ceiver reduces interference between the trans-mit and receive sections of the set. Controllingthis interference between the high-voltage drivepulses for the cathode-ray tube and the low signallevel at the camera output was the most difficultproblem in assembling the circuits into a unit.

The low-voltage power supply and the controlcircuits (as well as an equalizer where required)are contained in the service unit, which uses com-mercial power. Since no standby battery is pro-vided, failure of commercial power removes thevideo portion of Picturephone service (but doesnot affect the voice portion).

The Picturephone equipment that the Bell Sys-tem's customers will use has been designed withclose attention to human factors, to simulateas closely as possible the free and natural com-munication of face-to-face conversation. A mod-est graphics capability is included, and adjust-ments that people will have to make are limitedto those they are most likely to want. The ModII set is expected to serve well as Picturephoneservice becomes commercially available over thenext few years.

147

The first customers for Picturephone set -vice will likely be business and industrial en-terprises, where the usefulness is readily apparent. The service can be added to businesstelephone systems with some changes to present PBX and key telephone equipment.

Video Service for Business

S OME BUSINESS CUSTOMERS have simple, single-line telephone service much like residential

service. Others have special switching arrange-ments, either Private Branch Exchange (PBX) orcentrex, and many are equipped for key telephoneservice. (Centrex is a type of PBX service withadditional inward and outward dialing features.Key telephone service means pushbuttons on tele-phone sets to select additional lines and performother functions.) Together, these arrangementsprovide a broad array of telephone service fea-tures: attendant assistance, multiple lines with"pickup and hold," hunting from a busy line to asecretary, consultation hold, conference calling,call transfer, intercom, off-premise extensions,and many more.

PICTUREPHONE® service is a major new BellSystem service to be added to those now providedby the major dial PBX and centrex systems servingthe business community. For the most part, thecurrent systems are step-by-step and crossbar PBXswitching systems. These will supply PBX and cen-trex telephone service for several years to comeuntil electronic systems eventually displace them.

Let's look at what the business customer willsee and do in making a Picturephone call, what

May/June 1969

J. R. Harris and R. D. Williams

broad plans have been made for adding Picture-phone service to the various types and sizes oftelephone equipment, and what development pro-jects are now underway.

Initially, Picturephone service will be offeredto any customer served by selected No. 5 crossbarswitching offices. Customers will place and receivePicturephone calls much as they now do regulartelephone calls. With centrex service, incomingvideo calls can be connected directly to the Pic-turephone set; with either centrex or PBX ser-vice, calls can be switched to the set by an atten-dant. Picturephone display and control units canbe supplied for the attendant if the customer de-sires, so that the attendant can see and be seen.Another option would display a fixed video image,such as the customer's trademark, to the callerwhile the attendant is working on the call.

A new duty of the attendant will be to recognizewhen an incoming video call is directed to a non-video station and to notify the calling party thatthe video portion of the call cannot be completed.A question of best procedures arises when thecaller requests that the call be completed to avoice-only telephone. Systems will permit such aconnection, but charging will continue as if for

149

A new 850A PBX, operating in parallel with an ex-isting 701 or 757, will add Picturephone servicefor business customers. Both audio and video por-tions of Picturephone calls are handled by the

850A PBX. Voice-only telephone calls continue to beswitched by the regular PBX. Video and voice-onlycalls may be handled by the attendant; Picture-phone sets at the attendant's position are optional.

Picturephone service. A video call dialed directlyto a nonvideo line, however, will not be completed.

When a call involves more than two partiesequipped for video, there is no immediately ob-vious answer to the question of who should seewhom. In general, the party who has set up thethree-way connection determines who will seewhom (see table on page 153).

We expect that executives of medium and largebusinesses will be among the first customers forPicturephone service. Most of these customersare currently being served by the 701 step-by-stepor 757 crossbar systems. Other customers areserved by No. 5 crossbar centrex (see Choosingthe Route, this issue).

To add Picturephone service to the 701 and 757PBX's, Bell Labs has designed a new Picture-phone switching system, designated the 850APBX, which operates in parallel with the existingPBX (see figure on this page). The system in-cludes the service features generally availablewith other PBX and centrex systems. The PBX forPicturephone service uses the electronic technol-ogy exemplified by the 800A PBX (see ElectronicSwitching For Small PBX's, RECORD, February1967).

A new video line circuit connects each Picture-phone line to both the 850A PBX and the regularPBX. When a call is placed, the line is connected toa register in the 850A PBX and to a line finder orregister in the regular PBX. Picturephone callsare initiated by dialing the character, #, on the12-button TOUCH-TONE® telephone, followed bya normal telephone number. The # charactercauses the video switching system to dismiss theregular PBX and to apply a busy indication to theline appearance in that system. Both the audio andvideo signals are then handled by the 850A PBX.

Alternatively, if the called number is not pre-ceded by the dial indicator, #, the video switchingsystem is dismissed and a busy indication is ap-plied to its line appearance. The call is then han-dled in the usual manner by the regular PBX.

Interface between the regular telephone sys-tem and the video switching system appears atthree points (see figure above). The line circuitinterface involves only the talking pair and a su-pervisory lead for each line equipped for Picture-phone service. An interchange of signals is alsorequired for the attendant circuitry, which isshared between the two systems, and for the calltransfer circuits so that Picturephone calls can

1 50 Bell Laboratories Record

be transferred to a voice-only line. The videoswitching system is connected to the serving of-fice over special six-wire trunks.

Two parallel four-wire ferreed switches areused to switch the combined audio and videosignals for Picturephone calls. Crosspoints aremounted on new printed wiring boards designedto plug into carriers, which in turn are mountedon a framework similar to the existing PBX. Thenew PBX will serve a maximum of 90 lines.

When Picturephone service is added to a 701

or 757 centrex system, calls dialed directly to theoutside must be automatically identified (AIOD),

since no provision is being made for operator iden-tification. The 850A PBX will operate with theMOD system available for the 701 and 757 PBX's.

No. 101 electronic switching systems (ESS) are

May/June 1969

serving a growing number of customers. It is rel-atively simple to add the video capability to PBXand centrex services provided by No. 101 ESS. A

new four-wire wideband switch unit, which op-erates in parallel with the existing No. 101 ESSswitch unit, will be added to switch the video por-tion of the Picturephone call (see upper figure on

152). It will be capable of serving 150 orpage

more Picturephone sets. The program in the con-trol unit will control this switch. The audio por-tion of the call, as well as all supervisory func-tions, will be handled by the regular 2A, 3A, or 4A

switch unit in the normal manner. This arrange-ment uses the existing switch unit in handlingdata messages to pass control information backand forth between the control unit and the videoswitch.

A new video switch, operating in parallel with theexisting 2A, 3A, or 4A switch, will add Picture-phone service to the PBX and centrex services al-

ready provided by No. 101 ESS. The existing datalink (s) will be used for control of the video switchby the stored program in the Ess control unit.

Key telephone service will be used with PBX linesand with central-office lines. In either case, eachkey set can be served by one or more video lines,

intercom lines, and regular telephone lines. Whenused with a central-office line, a Picturephone in-tercom provides internal video communication.

152 Bell Laboratories Record

The wideband video switch uses standard, four-wire, 8-by-8 ferreed switches, packaged in mod-ules which can be added to the switch unit in thefield to increase the capacity of the system. This"add-on" type of growth encourages even distri-bution of traffic. The video switching network andassociated control will be packaged in cabinetscompatible with existing switch unit cabinets.

Further in the future, the 810A PBX, currentlybeing developed, will be designed to allow Picture-phone service to be added when desired by thecustomer.

To add the video dimension to the usual typesof key telephone service and to take care of cer-tain special situations as well, a new six-wirevideo key telephone system, belonging to the 1A2family of key systems, is being developed (seeKey Telephone Systems: The Latest Chapter,RECORD, March 1966).

A feature of the key system (see lower illus-tration on page 152) will be a single-link inter-com accommodating up to ten Picturephone sets.Calls to any set on the intercom will be madeby dialing the character, #, plus one other digitcorresponding to the called station. A multi-linkintercom is under consideration.

The key telephone system will include an add-on conference arrangement to operate with cen-tral office, PBX, or intercom lines. The conferenceunit will be similar to that provided for regulartelephone service, but only one video connectionwill be made at a time (see table on this page).

Video repeaters and synchronizing circuits-together with the usual lamp, holding, and audiblesignaling circuits-are required in the key tele-phone system to add Picturephone service. Anenlarged key service unit is planned to housethis equipment. This unit will accommodate twolines plus the equipment needed to switch the Pic-turephone set. The switching circuitry respondsto the pick-up key in the telephone set and per-forms the same function for video calls that thekey performs for audio calls. A four-line package,which provides four individual lines or two "boss-secretary" arrangements, will also be available.

In situations where the customer's telephone isserved directly from the central office, he mayelect to use key telephone service with central-office Picturephone lines. Each key telephone setcan be served by one or more video lines to thecentral office, video intercom lines, and regulartelephone lines.

When only a few people served by a PBX requirePicturephone service, they can be connected di-rectly to the central office, rather than to the PBX,

*These video services will be available with series 300and centrex II service. The controlling party must be aPBX or centrex station (never an "outside" party).Party A is the noncontrolling party first on the connection.The controlling party can add party B by flashing anddialing party B's number.

With Picturephone service, the communication system mustplay a part in control of who is seen in a three-party conference.

using key system arrangements just described. Inthis case the Picturephone number will usuallynot be the same as the PBX or centrex extensionnumber. On outgoing calls the customer will se-lect the video line to place a call by pressing anappropriate line button.

In the initial offering, Picturephone service isnot planned for off-premise extensions, tie lines,or interoffice channels used in common controlswitching arrangement (CCSA) services. In thefuture these services and new ones may be added.For example, the utility of video conferencesmight be improved. To this end a new voice-acti-vated conferencing system is being explored. Withthis arrangement the speech activity of the con-ferees controls who sees whom.

Compatibility with the Bell System's PBX, cen-trex, and key telephone system service features,together with maximum use of existing switch-ing capabilities and ease of installation andgrowth, have been the objectives of the PBX andkey telephone Picturephone planning and devel-opment.

May/June 1969 153

As Picturephone service supplements conventional telephone service, switching arrange-ments for video calls will be integrated with existing switching systems - initially withNo. 5 crossbar and later with No. 1 ESS - in the simplest and most direct way possible.

Choosing the Route

T

HE DECISION to integrate PICTUREPHONE® ser-vice with voice features leads directly to the

conclusion that the two must be combined inexisting local central offices. Thus, customers inan area will most likely receive Picturephoneservice from the same office that provides con-ventional telephone service. These customers willbe connected to the local office by the usual two-wire loop for voice, which can be used independ-ently, and a separate four-wire loop for the pic-ture, which can be used only with a voice loop.

On the outgoing side of the office, the voice andpicture transmission facilities will be combinedin a six-wire trunk and will never be used inde-pendently. For long-haul (or toll) connections,switching offices beyond the local level will be ar-ranged in a hierachy similar to that now em-ployed for telephone traffic. Since the Picture-phone signal will be converted to and maintainedin digital form as it is transmitted over morethan local distances, the toll offices will have dig-ital switching equipment.

May/June 1969

F. A. Korn and A. E. Ritchie

Within the local office to which the customersare connected, a separate video switching net-work is added, parallel with the existing voicenetwork, to interconnect Picturephone calls. Thisvideo network is called into play only when aPicturephone call is recognized. Remote switch-ing is used wherever possible to reduce the highcosts associated with long video loops.

Achieving the desired close relationship of voiceand video makes it desirable to use the same tele-phone number for both services. This, in turn,requires the use of a special indicator to differ-entiate video calls from voice-only calls. Thechoice of indicator is the twelfth button (#) ofthe TOUCH-TONE® telephone,used as a prefix, thereby tyingtogether Touch-Tone and Pic-turephone services. The sim-plicity and economy of thissignaling method easily justi-fies the tie-in, particularly inview of the long-range plan to

At a No. 5 crossbar central office inNew York City, switchman W. R. Ack-erson of the New York TelephoneCompany and co-worker J. N. Palmer(on screen) check operation of the Pic-turephone system currently being triedout by the Westinghouse Electric Cor-poration between its offices at NewYork and Pittsburgh, Pennsylvania.

P. N. Burgess and R. E. Lahr of BellLaboratories measure the transmissioncharacteristics of a wideband switch-ing network which simulates the morethan 12 million paths available in aNo. 5 crossbar office offering Picture-phone service. These tests were carriedout at the Columbus Laboratory inpreparation for the standard Picture-phone service planned for the 1970's.

Any one of these false conditions could causedegradation of the video signal.

Upon completion of the FCG test, the markerapplies a second continuity check to the callingcustomer video loop. Finally, before releasingfrom the call, the marker causes the outgoingtrunk to apply a 100-millisecond burst of a VideoSupervisory Signal (vss) on the video pair to-ward the calling customer, turning his Picture-phone set on. The signal consists of the sameseries of pulses that make up the horizontal andvertical sync pulses in a normal video signal butwithout the usual picture information.

At the terminating office, similar actions oc-cur, but with a few differences. For example,only a single check of the connection is madesince the trunk to the receiving office has alreadybeen tested and only the loop to the called stationneed be checked. In addition, vss is applied con-tinuously toward the called station, starting atleast 100 milliseconds before ringing begins. Thecombination of vss and the ringing signal causesthe station set to give a distinctive ring, indicat-ing a Picturephone call, and turns the set onwhen the customer answers.

Some readers may wonder at this point whethercrossbar switches, originally designed to pass au-dio signals up to 4 kHz in bandwidth, can handlevideo signals 250 times greater in bandwidth.They might also wonder whether the high-fre-quency noise generated by the operation and re-lease of hold-and-select magnets creates intoler-able interference with the video signal. Thesesame questions were raised early in the develop-ment of the Picturephone system. A concertedeffort by system, circuit, and equipment engi-neers, as well as an extensive testing program toverify the designs, helped answer them. Specifi-cally, it was necessary to learn about and reducethe effects of: the transmission insertion loss ofthe network over the 1-MHz band, the "self-cross-talk" properties of the network (i.e., crosstalkbetween the transmit and receive pairs of thesame channel), the crosstalk from other videosignals, and the noise caused by relay operationsin a central office.

Simply using equalizers to reshape video sig-nals distorted by the network would not workbecause the distortion of a signal would varyfrom call to call due to the differences in cablelength through the various paths or channels inthe network. Since this variability cannot rea-

May/June 1969

sonably be compensated by using fixed equalizers,a controlled floor plan for the wideband networki n the central office has evolved. The three-stagevideo switching network is thus arranged phys-ically so that variations in path lengths are heldto unusually precise limits: 160 feet, plus orminus 40 feet, from the wideband distributingframe through the three link frames to thetrunks, and 160 feet, plus or minus 10 feet, fromthe trunks back to the distributing frame.

Because the electrical distance between theequalizers and network is relatively constant,the design of the equalizers can be based on afixed cable loss and appropriate shaping. Allsignals coming from an equalizer to the networkpass through the wideband distributing frame ata predetermined level, making it possible to in-terchange equalizers and network terminationsfor such purposes as traffic balancing. All signalscoming from the network to the equalizers passthrough the distributing frame at a lower level,determined by the frequency-shaping character-istics of the controlled cable and network.

Further steps taken to improve transmissioncharacteristics through the office include: usingshielded cable for all transmission pairs betweenframes, separating each direction of transmis-sion into two separate cables, and separating thedo control leads from the transmission pairs. Anetwork with these constraints was built andtested. Also, system studies were conducted togive numerical limits to the transmission impair-ments described earlier, and to determine howeach of the impairments could be allocated toeach portion of the transmission path from Pic-turephone set to Picturephone set. The resultsof the testing program showed that the networkwill comfortably meet its allocation.

With the anticipated growth of Picturephoneservice, the No. 5 crossbar system will be ex-pected to provide new switching abilities. In theimmediate future, there is need to provide bitstream, or digital, switching arrangements forhandling the interconnection of calls above thelocal office level. Another need is for additionalcustomer features such as individual call trans-fer arrangements within a centrex group. Theseservices are being planned now.

For the longer range future, plans are beingformulated to switch Picturephone service withNo. 1 ESS and to provide better concentrator fa-cilities in the customer loop plant.

159

The Evolution of Picturephone ServiceSome recent milestones in the development of the PICTURE-

PHONE® system are summarized pictorially on these pages(photos from The Evolution of Picturephone Service,RECORD, October 1968).

1956

By this time, Bell Labs scientists had developed sev-eral experimental "video telephone" systems of varying

size and appearance which offered commercial possibilities. Theone shown here was demonstrated before the Institute of RadioEngineers on August 23. This was the first system to transmitand receive recognizable pictures over ordinary telephone wires.

1957 Studies and experiments continued at Bell Labs todevelop an economically feasible videotelephone sys-

tem. Experiments similar to the one shown here helped engi-neers establish such picture standards as resolution, contrast,and other f eatures. By 1959, plans were made to develop a video-telephone system specifically for the purpose of conducting trials.

1963 A complete experimental Picturephone sys-tem had been developed. The station set in-

cluded the camera-receiver-loudspeaker unit and theseparate combination telephone set-video control unit.

1964

The first public exposure of Picturephone service wasmade at the New York World's Fair. Visitors, selected

at random, tried the service for about 10 minutes each. Resultsof interviews conducted at the conclusion of each trial providedvaluable information on early public reactions to the service.

1965

As a result of earlier trials, significant equipment andoperational changes were made in the Picturephone

system. The modified equipment was used in a product trialbegun in July 1965, in cooperation with Union Carbide Corpor-ation. In December of the same year an experimental trial be-gan at AT&T headquarters in New York City. In June, 1967,the trial was expanded to include three Bell Labs locations. Thistrial integrated Picturephone service with normal telephoneservice. This "corporate network" offered an opportunity toexplore additional uses for the system, such as the feasibilityof using the Picturephone set as an interface between man andcomputer (shown here). The computer is interrogated from aTouch-Tone® dial, and results are displayed on the screen.

1964 Limited commercial Picturephone service be-tween public locations in three cities-New

York, Chicago, and Washington, D. C.-began on June.25. The service was inaugurated with a call from Mrs.Lyndon B. Johnson in Washington to Bell Laboratoriesscientist Dr. Elizabeth A. Wood, at the Picturephonecenter in Grand Central Terminal, New York. RobertF. Wagner, then mayor of New York, is seated at right.

1968

The Bell System's Picturephone "see-while-you-talk" set has been redesigned to in-

corporate additional features as a result of theextensive trials. The improved "Mod II" set shownhere is itself now the subject of further trials asthe evolution of Picturephone service continues.

Transmitting Picturephone signals across town and across the country takes advantageof the versatility of today's nationwide communications network. Digital systems to beintroduced in the future will greatly increase transmission efficiency and versatility.

Transmission Across TownOr Across the Country

T

HE BELL SYSTEM NETWORK has come a longway since the first telephone customers were

connected over the simplest form of transmissionsystem-wires. Today, the transmission networkis a complex aggregate of electronics gear andthe transmission medium (wire lines, coaxialcables, and radio paths). Together, they providea multiplicity of channels over which many cus-tomers can communicate. New and more complexservices and equipment are continually beingadded to the network without disrupting or im-pairing its ability to handle the many and variedexisting communication services. The introduc-tion of PICTUREPHONE® service is no exception.Adding Picturephone service to the networkmakes it more versatile and potentially useful fora variety of wideband communication services.

Basically, the transmission objectives for Pic-turephone service are to transmit high-qualityvoice and video signals and to maintain this qual-ity from one call to the next. One criterion infulfilling this objective is to make the audio por-tion of a Picturephone call at least as good asit is in the present DDD network. Because we ex-

162

D. W. Nast and I. Welber

pect that customers will normally use a form ofspeakerphone during a Picturephone call, theacoustics of the customer's office or home may af-fect the quality of the audio signal. Thus, controlof echo and loss has been given special attentionin engineering the network.

The greatest challenge, however, is the videotransmission. To assure adequate picture quality,stringent requirements have been placed on suchtransmission characteristics as amplitude andphase deviations, single-frequency interference,random noise, crosstalk, switching noise, gainvariation, low-frequency response, and powerhum. As an example, for each trunk, interferingsignals from power lines must be at least 45 dBbelow the desired signal. The requirements havebeen set to assure satisfactory performance onconnections involving up to six analog trunks intandem.

The Picturephone signals, both audio andvideo, arrive at the local central office in analogform over six-wire "loops"-two wires for audioand two wires for each direction of the video por-tion. Special six-wire trunks are then used to

Bell Laboratories Record

carry the call outside the local area. Basebandanalog transmission is used over exchange trunksless than six miles in length. For longer exchangetrunks and toll trunks, analog transmission couldalso be used, but it would not be a very practicalsolution, economically. Although the analog re-quirements for long-haul Picturephone trans-mission could be easily met by using an entireTD-2 channel, just as for television, this wouldbe prohibitively expensive. And it is not possibleto put together an efficient combination of analogvideo signals without suffering greater impair-ment than is allowable on long trunks.

What is the solution? It turns out to be moreeconomical for most of the longer exchangetrunks, and for toll trunks, to transform the an-alog signal to digital form, and convert it backto analog at the distant terminal. And this iseasy to do, since digital transmission in the BellSystem is evolving rapidly. There are two veryimportant characteristics of digital transmissionthat ideally suit it for this application. First,the digital signal can be regenerated so that theimpairments are not a function of distance. Sec-ondly, once they are in digital form Picture-phone, telephone, and data signals can be effi-ciently intermixed on the same transmissionfacility. By taking advantage of these charac-teristics, line impairments-error rate and pulsejitter-can be so controlled that their effects onthe Picturephone signals are essentially imper-ceptible.

Information can be sent in a digital formatover transmission systems that use frequency-division carrier techniques for carrying severalsignals simultaneously. Sending voiceband dataover the switched DDD network is an example.Digital information can also be sent over systemsusing time-division techniques for handling sev-eral pulse streams at one time. The T-1 system,for example, with its pulse stream of 1.5 mega-bits per second (Mb/s), is the Bell System's mostwidely used system that is inherently digital inits makeup. But its capacity isn't sufficient tohandle a Picturephone signal. However, the T-2carrier system, a member in the same family tobe introduced shortly, carries a 6.3-Mb/ s signal.The Picturephone signal can be adequately rep-resented using this bit rate. Although a higherbit rate would have made it easier to get the de-sired performance, it would have been extrav-agant from a transmission point of view.

With the decision to use the 6.3-Mb/s rate cameanother one-to limit the encoding to a singlestep (i.e., once the signal is in digital form itstays in this form until it reaches the analog

May/June 1969

connecting line at the far end). The toll networkused for Picturephone service can be administeredto avoid multiple encodings by appropriate engi-neering of the switching hierarchy.

Encoding the Picturephone signal into digitalform at a 6.3-Mb/s rate raises the question ofoptimum format. Before we can answer thatquestion we must know something about the

Ralph Graham, of AT&T's Long Lines Depart-ment, checks the operation of the digital terminaldeveloped for the TD-2 microwave system. Thisterminal handles signals for the trial now inprogress between Westinghouse Electric Corpo-ation's offices in New York City and Pittsburgh.

1 63

Bell Laboratories Record1 64

(Refer to (A) on previous page.)Picturephone signals are encoded into digitalf orm for transmission over long distances usinga "differential PCM" system. The Picturephonesignal (A) is an analog of the picture material.

(Refer to (B) on previous page.)Encoding the analog signal into a pulse streamwith a standard Pcm system (B) would result inan excessively grainy picture. The 1-MHz videosignal is sampled at a 2-MHz rate. Three binarydigits are used to code the samples. But withthree digits only eight discrete levels can be en-coded, which for purposes of this example aredivided equally over the maximum amplitude ofthe signal. The use of only eight levels for sam-pling a continuous signal results in the graininess.

(Refer to (C) on previous page.)The differential Pcm system (C) appreciably re-duces graininess by taking advantage of theunique characteristics of the signal-i.e., most ofthe energy is below 50 kHz and the amplitudechanges very little. Here a delayed signal, pro-duced from a PCM decoder in a feedback loop, issubtracted from the original signal. Most of theeight discrete levels are arranged to represent theregion o f the difference signal around zero; fewerlevels are used for larger difference signals. Al-though the reproduction of a picture coded inthis way is still grainy, tests have shown that itis far superior than one coded by straight PCM.

May/June 1969

form of the signal itself. Take the energy con-tent of the signal, for example. Imagine a spe-cial power measuring device that measures thepower in a narrow frequency band. If we wereto measure the energy content of the signal innarrow steps from very low frequencies (dc) to1 MHz as a function of time and average eachreading over the time interval, a plot of the re-sults would show that most of the energy is con-tained below 50 kHz. Moreover, the curve wouldshow that for much of the time the signal ishardly changing at all, or if it is changing rap-idly and introducing high frequencies, it is notdoing so very often. These properties, as we willsee later, are used in deriving an efficient digitalcoding scheme for Picturephone signals.

To encode the 1-MHz video Picturephone sig-nal into the T-2 rate of about 6 Mb/s takes twobasic steps: sampling and coding. Samples of thevideo signal must be taken at a rate which is atleast twice the highest frequency we wish to re-produce. This is a fundamental law of communi-cation. Thus, if we wish to reproduce a picturewith resolution up to 1 MHz, we must samplethe amplitude of the original signal at least at a2-MHz rate. Limiting the transmission rate to 6Mb/ s means we are restricted to three binarydigits per sample. However, three binary digitsmean that the total amplitude range of the signalmust be represented by only eight discrete levels(see B at left).

So far we have done two things-one beneficialand one restrictive. We have substituted a signalthat is either on or off for one that previouslyhad a continuous range of values-this is bene-ficial since a two-valued signal can be reliably re-produced with no loss in information as long asthe on pulse can be distinguished from the offpulse. The restrictive effect is that the signal isnow represented by only eight levels, where be-fore sampling and coding it was continuous. Thiseffect produces a graininess in the picture whichmost people would find quite objectionable. Toovercome graininess, a process called differentialPcM is used. This process takes advantage of thefact that most of the energy in the signal is be-low 50 kHz, and the amplitude is hardly chang-ing at all.

The encoder used for differential PCM (see Cat left) employs a PCM decoder in a feedback loopwhich produces a signal that is delayed by asmall amount from the original. The delayed sig-nal, when subtracted from the original, producesa difference signal. When the original signal ischanging slowly or not at all, the difference iszero, or nearly zero; when the signal is changing

165

For the present, and until the early 1970's, TD-2microwave radio is one, of the two means fortransmitting Picturephone signals over long dis-tances. To do this, a special digital multiplexand a digital terminal were developed to encodeup to three Picturephone signals on one TD-2radio channel. The digital multiplex combines

the three 6.3-Mb/ s Picturephone signals plus therequired synchronizing and framing pulses into a20.2-Mbls signal. The digital terminal convertsthis signal into a high-speed, four-level pulsetrain. The FM terminal transforms the pulsetrain into a frequency-modulated wave, which issent to the TD-2 microwave radio transmitter.

A special digital multiplex and terminal is beingdeveloped to permit the L-4 coaxial cable systemto carry digital Picturephone signals over longdistances. The signal produced by the terminalused with the L-4 system is a pulse stream with

eight-level pulses instead of the four levels usedin the TD-2. Two digital Picturephone signals,applied to the L-4 system, can occupy the fre-quency band normally used .for any of the L-4mastergroups except the bottom mastergroup.

166 Bell Laboratories Record

rapidly, the difference is large. At this point wetake advantage of the fact mentioned earlier thatmost of the time the signal is changing slowly,and thus, most of the time the difference signalwould be near zero. This being the case, we canarrange the eight coding levels so that most ofthem are used to represent the region aroundzero. Fewer levels are used for the larger differ-ence signals. The reproduction of a picture codedin this way is still subject to some graininess whenthe signal is changing rapidly, such as a rapidchange from black to white or vice versa. How-ever, the results of subjective tests performedwith a coder of this type are far superior thanfor a straight Pcm coder.

The digital transmission system that will carrythe signals between distant points can assume avariety of forms. For the present, and until theearly 1970's, TD-2 microwave radio and the L-4coaxial cable system will handle most Picture-phone signals. The T-2 digital carrier system,first of the toll digital systems scheduled for in-troduction in the early 1970's, will carry Picture-phone signals, where appropriate, over interex-change trunks for distances up to several hun-dred miles. Still further in the future, the L-5and T-5 coaxial cable systems and eventuallymillimeter waveguide will be available for long-haul transmission of Picturephone calls.

Since the TD-2 and L-4 systems are designedaround frequency-division carrier techniques,they require special terminals to permit digitalsignals to be transmitted efficiently. The specialdigital terminal developed for the TD-2 (seeupper figure on facing page) will enable up tothree encoded Picturephone signals plus the re-quired synchronizing and framing pulses to becarried on one radio channel. The bit rate on theradio channel will be 20.2 Mb/ s. The format ofthe signal applied to the TD-2 channel consistsof the 20.2-Mb/s digital pulse train with eachpulse having four possible levels. A single pulse,therefore, carries two information bits, and thepulse rate on the channel is 10.1 million pulsesper second. Evaluation of the performance of thissystem shows it to be highly satisfactory. Evenwhen the radio channel undergoes selective fad-ing and is about to switch to the protection chan-nel, the maximum error rate in the digital signalis less than one in 100K. This produces a barelyperceptible amount of noise in a Picturephonesignal.

The L-4 coaxial cable system (see lower figureon facing page) is not subject to fading or largevariations of noise level, and accordingly, the for-mat of the digital signal is different. The signal

May/June 1969

produced by the digital terminal being developedfor the L-4 system is a pulse stream with eight-level pulses instead of the four levels used in theTD-2. In addition, a special signal format, knownas "partial response" filtering, takes advantage ofthe properties of the coaxial cable. This formatproduces a spectrum with essentially no energyat the band edges of the mastergroup. (A master-group is a composite signal which carries up to600 voice channels.) This is done to minimize in-terference into adjacent channels and to permittiming and synchronizing signals (pilots) to beplaced at the band edges.

Two digital Picturephone signals, applied tothe L-4 system, occupy the frequency band nor-mally used to carry a single mastergroup. TheL-4 system can carry six mastergroups. Any or allof the mastergroups may transmit encoded Pic-turephone signals, with the exception of thebottom mastergroup. The distortion introducedby the repeaters in the band set aside for thebottom mastergroup is more severe than in theother mastergroups, and the performance fordigital transmission is, therefore, inadequate.

When only a few toll trunks are needed, TD-2and L-4 systems will take care of these Picture-phone requirements quite handily. But laterwhen many such trunks are needed along a majorroute, new digital 'systems will provide the mosteconomical answer. It works out this way: Formessage channels, the analog systems using ra-dio and coaxial cable are very efficient, and evenT-5, a family of digital systems for possible useon coaxial cable in about 1975, will probably bea slightly costlier way of getting voice circuitsthan will its analog cousin, the L-5 coaxial cablesystem. But the digital systems will have amarked advantage when it comes to handlingPicturephone signals because of the tradeoffsinvolved. For example, a TD-2 radio channel cancarry 1200 message channels but only three Pic-turephone channels-a tradeoff of one Picture-phone channel for 400 message channels. Sim-ilarly, the L-4 system substitutes two Picture-phone channels for 600 message channels, or onePicturephone channel per 300 message channels.In contrast, the T-2 carrier system, designed es-pecially for digital transmission, will displaceonly 96 message circuits to carry one Picture-phone channel. And future digital systems, suchas the T-5 system, will have a corresponding ad-vantage over future analog systems in efficiencyfor transmitting Picturephone signals.

The discussion thus far has covered the methodused to transmit the Picturephone signal overlong distances. We must also transmit the signal

167

over shorter distances (about six miles or less)between central offices. Transmission of Picture-phone signals over this distance is in analogform over interoffice exchange trunks. The ex-change cables can be as large as 1100 pairs of22-gauge wire in one sheath and are presentlyused for two-way transmission of 4-kHz telephonechannels. Trunk facilities are made up of six6000-foot sections in tandem, and as many asfour trunk facilities may be built up to completea connection between central office switches.Transmission of a 1-MHz video signal over thismedium with minimum degradation of the sig-nal requires precise equalization. Thus, equalizerswill be placed every 6000 feet, with power sup-plied over the same line.

The equalizer contains several networks thatcompensate for the distortion introduced by vari-ation of attenuation with frequency in the cable.Equalizers are designed to have the equivalentattenuation of cable lengths of 3000, 1500, and750 feet, thus restoring all frequencies to theiroriginal intensity. One network, which matchesthe characteristics of a 750-foot length, is vari-able to accommodate variations in the length oftrunks, or variations in characteristics that canbe equalized by an equivalent change in length. Atemperature-regulation section is also included toavoid seasonal adjustments of the equalizers. Thenormal variation of cable temperature over theperiod of a year can cause the transmission to

1 68

change enough to give excessive distortion. Infact, a 5-degree change in cable temperaturewithout a corresponding change in the equalizersetting will cause appreciable distortion. To com-pensate for this, a temperature regulating equal-izer responds to changes in the level of a 1-MHztone, applied to the trunk continuously.

The previous discussion assumes that the vari-ous pairs in a cable have the same loss versusfrequency characteristic and the same temper-ature coefficients. This is not the case, and forthis reason a "mop-up" equalizer, operating onthe same 1-MHz signal used by the line equalizer,will be provided at the receiving office of eachtrunk. The 1-MHz tone is supplied continuouslyby each outgoing office equalizer. An additional100-kHz tone, used at the incoming office to pro-vide a second reference point for mop-up equal-ization and temperature regulation, is also sup-plied by the outgoing office equalizer, but onlywhen the Picturephone signal is not present.

It seems certain that future work on trans-mission systems to carry Picturephone signalswill be concentrated on increasing transmissionefficiency. The introduction of new digital trans-mission systems in the 1970's will be a majorstep toward meeting this objective. In the mean-time, our ability to send high-speed digital in-formation over existing analog systems is a prac-tical beginning for a digital network that canreach virtually every part of the country.

Bell Laboratories Record

Telephones are connected to central offices over a vast network of aerial and under-

ground wires called the customer loop plant. This network will soon carry video as well

as voice calls, as the new Picturephone service evolves and becomes more widely used.

Connecting the Customer

IN THE 1970'x, PICTUREPHONE® service will beoffered by the Bell System over existing cus-

tomer loops, just as many special services are of-fered today. These wire networks, built up overthe years primarily for economical voice com-munications, will soon take on the more stringentrequirements of video transmission. While somechanges will obviously be required, the loops willremain basically.the same. Picturephone servicewill be incorporated by modifying existing loops,not by replacing them.

Adapting customer loops to accommodate Pic-turephone service depends upon a number offactors, including distance of customer from theoffice, age of wire facilities already there, prox-imity of interference sources, type of plant con-struction (aerial or underground), and the areabeing served (urban, suburban, or rural).

The existing loop plant consists of conventionalwire pairs, each telephone line requiring onepair. For two-way video transmission, two addi-tional wire pairs must be used, forming a six-wire

May/Tune 1969

F. T. Andrews, Jr., and H. Z. Hardaway

loop for two-way Picturephone service. The ex-isting loops are designed for transmission ofvoice signals, which are in the 4-kHz frequencyrange. But the video frequency band is muchwider-about 1 MHz-so that transmission lossesare much greater, and some form of signal re-constitution is needed. This is where equalizerscome in.

Adding equalizers is the most significantchange required to adapt existing loops for Pic-turephone service. The equalizer is a basic re-quirement of Picturephone loops, providing gainequal and opposite to the loss of ordinary tele-phone cable pairs within tenths of a decibelacross a frequency band from 1 Hz to 1 MHz.Determining how many equalizers should beadded, and where, is essential to make best useof existing plant.

For example, there are practical limits to howlong a section of cable can be handled by anequalizer at a given location. While separate pairsare used for transmitting video signals to and

169

The need for equalizers in a cable carrying 1-MHz video signals is evident in this example ofthe loss of two lengths of 22-gauge pulp-insulatedcable. For a given gauge, plastic-insulated con-ductor cable has somewhat less transmission loss.

When equalizers for both directions of transmis-sion are installed at the same physical location,there is some possibility that the output of onecan feed into the input of the other via crosstalkpaths (arrows) and cause "singing." This is pre-vented by keeping the combined gain of the equal-izers from exceeding the combined loss of thecrosstalk paths, using shorter equalizer spacing.

from the customer (in addition to a single pairused for transmitting voice signals in both di-rections), for practical reasons equalizers for thetwo directions are installed at the same physicallocations along a cable run. As a result, the out-put of one feeds into the input of the otherthrough the undesired but inevitable near-endcrosstalk paths (see illustration on this page).

170 Bell Laboratories Record

Should the combined gain of the equalizers ex-ceed the combined loss of the crosstalk paths atany frequency in the band, high-level oscillationswill result. This is, of course, most likely to hap-pen at the higher frequencies, where the equal-izer gain must be high and crosstalk loss is low.Transmitting two directions in separate unitswithin the same cable helps, but is not alwayspractical. Thus, maximum equalizer spacingshave been established for the wire gauges beingused in Picturephone loops (see table on page172), limiting the gains to values unlikely tocause high-level oscillation.

Actually, two different versions of the equal-izer are required to satisfy the transmission re-quirements of Picturephone service (see illus-stration on page 172). One version is adjustableto match the characteristics of sections of cable;the other has fixed gain and frequency character-istics to match runs of wire within central of-fices. Build-out networks and test access points(not shown in the illustration) are necessary toalign the system. The equalizers located in man-holes are powered in series over the same pairsused for signal transmission.

The equalizers cannot be adjusted to match thecable characteristics perfectly, nor do they trackthe changes in those characteristics caused bytemperature variations. Each equalizer sectioncontributes some residual distortion which, if al-lowed to accumulate, would be manifested as"echoes" or ghost images at the Picturephoneset. The resulting deterioration of the picture de-pends directly on the intensity of the ghost im-ages and the extent of their separation from themain image. As a way of measuring this kind ofproblem, signal distortion is translated into whatis called an "echo rating," which is an overallevaluation of the transmission characteristics ofa loop with equalizers added for video service.

To determine whether existing customer loopsare suitable for high-frequency signal transmis-sion, the performance of these loops with equal-izers added is simulated on a computer. The sim-ulation program decides where equalizers areneeded and simulates the adjustment they wouldreceive in the field. The resulting echo rating in-dicates whether the particular loop configurationis suitable for system use.

Picturephone service will first be offered in ur-ban areas. Tests of selected loops in New YorkCity and Pittsburgh have confirmed that existingfacilities in those cities can be used for Picture-phone service, as it is now planned. (A producttrial between these two cities is now being run,in cooperation with the Westinghouse Electric

May/June 1969

T. A. Sickman of Bell Laboratories tests and adjusts equalizersto be used in Picturephone loops. The equalizers are connectedto a 6000-foot length of test cable to simulate a customer looparrangement. In addition to providing gain compensation,equalizers are used to correct distortion of the video signal.

The video portion of a Picturephone loop is addedin parallel to the existing telephone loop network.

Corporation.) As the service is extended towardsuburban areas, many additional factors willhave to be considered.

Customer loops for ordinary telephone service,for example, are designed to resistance limitswhich insure satisfactory dialing and talking re-gardless of the distance between the office andthe customer. This is accomplished by using arange of wire gauges (19, 22, 24, and 26 gauge)and adding inductances, called loading coils, at6000-foot intervals on loops longer than 18,000feet. It is common to find a combination of wiregauges and both paper pulp and plastic-insulatedconductors in a single customer loop. Such anarrangement appears to be satisfactory for ini-

The maximum cable lengths shown take into ac-count variations in cables and underground tem-perature. They will be used as guides for install-ing equalizers in loops for Picturephone serviceexcept where special circumstances, such as highimpulse noise levels, necessitate closer spacing.

172 Bell Laboratories Record

Equalizers in manholes are powered in series overthe same wire pairs used for signal transmission.

tial urban Picturephone service. But, as theservice expands, all the various transmission ir-regularities at video frequencies will have to bechecked carefully.

Additionally, it has always been difficult to pre-dict the growth pattern of the lines and servicesfor a central office area, and to predict needsalong any given cable route. These uncertainties,and the fact that it is difficult to get at indi-vidual wire pairs in pulp-insulated distributioncable, have led many telephone companies to in-stall cables with "bridged taps." That is, several"taps" are connected to the individual wire pairsat intervals along the cable as it is installed.Eventually one tap on a pair is used to connecta customer's telephone service; the unused con-nections are called bridged taps. Loops containingbridged taps more than 100 feet long cannot beequalized adequately for Picturephone service.Survey results show that the overall Bell Systemaverage bridged tap per main station is 2500 feetlong. Thus, removing bridged taps will be a nor-mal step in preparing loops for video transmis-sion.

Further growth in dedicated outside plant (seeAccess and Control Points for Dedicated OutsidePlant, RECORD, February 1967) and unigauge(see Unigauge-A New Subscriber Loop System,RECORD, September 1967) will eventually resultin a plant more uniform and easier to adapt forhigh-frequency services. In the dedicated plantconcept, pairs without long bridged taps arepermanently assigned to existing and probable fu-ture customer locations. The unigauge conceptmakes it possible to serve customers up to almost6 miles away from a single central office, usingonly 26-gauge wire and range extenders from cen-tral office to customer. These and other concepts

will be incorporated as Picturephone servicegrows, thus helping to assure the successfulblending of old and new services and facilities.

Another consideration in designing equalizersfor customer loops is the variation in transmis-sion losses resulting from temperature changesin the cable. The temperature range for buriedplant about 18 inches down is about 32 to 75 de-grees F. Temperature variations of aerial plant,on the other hand, track the surrounding airtemperature, and increase about 20 degrees morewhen there is direct warming by the sun. Today,the trend is toward placing all new plant under-ground wherever possible. By 1975, practicallyall new residential distribution cable installed bythe Bell System will be out of sight. This trendwill help reduce both seasonal and day-to-day tem-perature changes in the loop plant, and thus pro-mote more stable electrical performance.

As Picturephone service spreads into the sub-urban and rural areas, there may be a problemwith radio-frequency interference, since much ofthe loop plant in these areas includes aerial cable.Unshielded aerial drop wires act as antennas forradio waves impinging upon them, and the 1-MHzrange of the video signal overlaps the 0.5-to-1.6-MHz range of powerful commercial broadcasttransmitters. Shielded drop wires and accessterminals, short equalizer spacing, and low-passfilters can all be used to combat interference. Thespecific approaches used will depend on each par-ticular situation. Studies are under way to im-prove our understanding of the interference tobe expected in the frequency range of Picture-phone signals.

Like all significant changes in the customerloop plant, the introduction of Picturephoneservice will require revisions to current plan-ning, engineering, installation, and maintenancemethods. Techniques of dealing with interferenceand the other problems will evolve as they havein the past. The administration of Picturephoneloops also will be more involved. Since these loopscontain equalizers, they cannot be rearranged assimply as conventional telephone pairs, but willhave to be segregated in much the same way thatspecial service loops are today.

Further in the future, improved new cable de-signs, which have been under development forvoice use, will also help us do a better job ofmeeting the combined needs of voice and videotransmission. Just as the present ways of engi-neering and constructing loops have grown outof successive improvements, so too will the Pic-turephone loop network evolve as we learn andprogress from each successive experience.

May/June 1969

M. F. Veverka and E. W. Banz, Jr., both of Bell Laboratories.measure electric field strength and the associated interfer-ence on telephone lines to help determine the need to preventradio frequency interference with the 1-MHz video signal.

173

The Picturephone system is possible in an economical form because of recent develop-ments in electronic components technology. How recent is best illustrated by the inte-grated circuit devices in the display unit, as well as by its picture and camera tubes.

Devices-The Hardware of Progress

A

NYONE SCANNING a list of the electronic de-vices used in the PICTUREPHONE® system will

gain insight into the meaning of technologicalevolution. On this list are devices that wouldhave been impossible to produce only a few yearsago-devices, for example, that draw heavily onrecent silicon and thin-film technology. This ar-ticle will limit itself to describing eight devicesthat most clearly embody the latest advances inthe technology of electronic components: the pic-ture tube, the camera tube, and six integrated-circuit devices. All eight were expressly designedfor the Picturephone display unit.

The picture tube is an electrostatically focusedcathode-ray tube with magnetic deflection. Of theeight devices, it is the only one the customer willsee and, inevitably, it will remind him of hishome television set. However, there are signif-icant differences-most of which add up to greatersafety, reliability, and economy of installation.

May/June 1969

S. O. Ekstrand

For example, the tube's deflection yoke is posi-tioned during manufacture and then permanentlyfastened in a polyurethane encapsulation. In ad-dition, frame-centering projections are moldedinto the encapsulation so that the tube can be eas-ily centered in its enclosure. These and other fea-tures make installation a relatively simple job-and a safe one, since the rock-hard polyure-thane also serves as a protective shield. A fur-ther margin of safety is supplied by a glass panelthat is bonded to the face of the tube. This panelserves a double purpose: Its surface is lightlyetched to reduce glare in brightly lighted rooms.

Like all telephone devices, the display tube hadto be designed for long life. Its envelope is madeof a special glass that is highly resistant to thediscoloration caused by electron bombardment,and all of its electrodes are designed to meet ex-acting electrical tolerances. A case in point is thecutoff voltage required for grid number one.

1 75

This voltage is the minimum needed to stop theelectron-beam flow entirely. In the drive circuitof an average cathode ray tube, the cutoff voltagewould have to have an allowable range of 30 voltsor more. In the Picturephone set, however, thecutoff voltage needs a range of only 15 volts,which permits more economical circuitry. Whatmakes this reduced range possible is precise con-trol of spacings and grid aperture sizes duringmanufacture.

In life tests, the tubes have been living up totheir design objectives and continue to deliverhigh and constant output. They show negligibleloss in brightness after eight to ten thousandhours of continuous operation, and there havebeen no indications of discolored glass.

The camera tube is even more a product ofmodern technology than the picture tube. (SeeA "Solid-State" Electron Tube for the PICTURE-PHONE Set, RECORD, June 1967). This unusualtube uses a target consisting of an array of morethan half a million silicon diodes in an area ap-proximately one-half inch on a side. The diodesare reverse biased and scanned by an electronbeam. A thin resistive film over the target's faceprevents the beam from charging the silicon di-oxide surface to the point where it would reflectthe beam.

One of the things that can affect the tube's

Cutaway view of the Picturephone set's cameratube (top). The silicon target is immediately be-hind the lens at the right. Thin enough to betranslucent, the target has over half a millionsilicon diodes in an area about the size of anickel. Like the display tube, the camera tubeuses electrostatic focusing and magnetic deflec-tion. The entire tube is shielded by high-permea-bility magnetic material. The insert below thecamera tube shows the "mesh" electrode, whichf orms a uniform field between itself and the target.

(Bottom) The display tube is essentially a "plug-in" device and requires no adjustments duringinstallation. The deflection yoke is positionedduring manufacture and permanently set in placewhen the tube is encased in polyurethane plastic(shaded area). Projections molded into the plasticmake it easy to center the tube in the display set.

May/June 1969

performance adversely is the target's "dark cur-rent"-that is, the leakage current generated bythe diodes even in total darkness. Excessive darkcurrent limits the maximum contrast of the pic-ture. The problem is created by two kinds of darkcurrent, known as "surface generated" and "bulkgenerated." The surface-generated dark currentis due to surface-state energy levels that exist atthe silicon dioxide interface. Although these en-ergy levels arise from a number of differentcauses, they can be collectively measured and con-sidered as a single phenomenon. At one time, thesurface-state energy levels were a major sourceof dark current, but improved processing of thesilicon target has virtually eliminated this prob-lem. Similarly, bulk-generated dark currents-which are due to the activity of charge carrierswithin the bulk of the silicon-are now held to aminimum by proper processing of the silicon.

The structure of the electron gun also plays apart in holding down dark current: The gun'selements are arranged so that all light from thecathode and heater is barred from the target, anddark current due to this light is minimized.

Mechanical strength and alignment of thenewer tubes have also been much improved. Thegun's electrodes and ceramic spacers are brazedtogether by a pass through a furnace. And to en-sure accurate alignment of the beam-strippingelectrode (which trims the beam's diameter to0.003 inch), laser technology is called upon: Theelectron-gun structure is completely assembledand then a pulsed ruby laser is used to drill a0.003-inch hole through the beam-stripping electrode. The resultingalignment is precise enough to guar-antee maximum beam transmission.

The mounting of the silicon targethas a minimum number of parts, sothat manufacture is simplified and ca-pacitive coupling between the target andother elements is mini-mized. In addition, the ex-ternal terminal of the"mesh" electrode (which.forms a uniform field be-tween itself and the target)has been placed close enoughto the target area to allowa common ground reference for both themesh and the target. This arrangementeliminates ground loops between these ele-ments and minimizes noise from inducedcurrents.

The camera tube is supplied ready foruse and comes with its magnetic deflection

coils prepositioned. The electron beam is mag-netically aligned within the gun during manu-facture, and the tube is enclosed in a high-perme-ability magnetic shield. All of this eliminates theneed for any adjustments after manufacture,which means that the tube is essentially a plug-indevice.

The six integrated circuit devices that controlthe camera tube are the products of the same up-to-date technologies. The devices are: a voltageregulator, a linear video gate, a video gate logiccircuit, a synchronizing clock oscillator, a syn-chronizing tip generator, and a synchronizingclock logic system.

The voltage regulator maintains a critical sup-ply voltage for the sync clock oscillator and thehorizontal and vertical sweep generators for thecamera tube. It is designed to supply 12 volts( ± one percent) with a load carying from -10to -30 milliamperes do and line voltage varyingfrom 16 to 24 volts do over a temperature rangeof 0 to 60 degrees C. Physically, the regulatorconsists of three silicon chips-a junction field-effect transistor, a voltage reference diode, anda silicon monolithic integrated circuit. All threeare mounted in an eight-lead transistor type en-capsulation that has adequate power dissipationcapabilities.

The sync clock system supplies all of the tim-ing signals for the Picturephone set's camera.These signals control the horizontal and verticalsweeps, camera blanking, gating for the auto-matic gain control and video clamping, and theformation of the sync output signal. The precisetime constants needed to maintain precision areachieved with thin-film capacitors and resistors.Amplification and buffering functions are handledby a separate silicon monolithic integrated cir-cuit chip. A similar combination of thin-film and

silicon integrated circuits is usedfor the sync tip generator. Thiscircuit provides an accuratelytimed pulse that is combinedin the sync clock logic cir-cuitry to form the sync out-put signal.Two "count-by-16" cir-

cuit chips plus a "mis-cellaneous logic" chipsupply the necessarylogic for converting theoutput of the sync clockoscillator and the synctip generator into therequired six timingsignals. The count-by-

16 circuits include a complete four-stage binarycounter and use 72 transistors and 111 resistorsto form 40 logic gates. These gates are designedto assure reliable low-power operation even withconsiderable variation in component parameters.Their high tolerance for variation makes possiblehigh manufacturing yields-another contributionto economy.

The count-by-16 circuits are used to divide thesync clock oscillator's basic frequency of 16.26kHz to get a vertical sweep frequency of 60 Hzand ensure precise field interlacing. A similar,"miscellaneous logic" chip supplies 46 logic gatesof the kind used in the count-by-16 circuits.Made up of 74 transistors and 116 resistors, thechip handles all the gating for the timing func-tions that control the camera tube. This circuithas the most logic gates per chip and the highestpacking density of any integrated circuit pres-ently being supplied by the Western ElectricCompany.

The complete video gate is made up of two sili-con monolithic integrated circuits. One, a linearvideo gate, is a single-pole, double-throw switchfor coupling the desired video signal through tothe output with negligible loss, while providingalmost total isolation from undesired signals. Itis used to achieve the MONITOR feature as well assome other features. The second of the two mono-lithic circuits is a video-gate logic circuit thatdrives the appropriate indicator lamp on the con-trol unit and also supplies do control signals forthe linear video gate circuit.

To produce these devices in a reasonableamount of time without sacrificing reliability oreconomy, Bell Labs device designers had to workvery closely with designers of the Picturephoneset and with the Western Electric Company engi-neers who will eventually be responsible for man-ufacturing them. To smooth the transition fromdesign to manufacture, a joint development andmanufacturing facility was installed-at the BellLaboratories location at the Western ElectricPlant in Reading, Pennsylvania. Planned by ateam of engineers from Bell Labs and WesternElectric, this installation has facilities for de-veloping all the devices described in this article.All planning was done with an eye toward earlypilot manufacture.

The fabrication area is a series of clean roomsspecifically designed to satisfy the stringent re-quirements of semiconductor and electron tubemanufacture. The area is supplied with filteredand air-conditioned air, which is monitored toensure a dust count no greater than 500 particlesper cubic foot. The flow is pseudolaminar, with

Bell Laboratories Record

Glenn Hill of the Western Electric Company makes final mi-crometer adjustments of an encapsulation mold for the Picture-phone display tube. The adjustments accurately position thetube before polyurethane is poured in. Centering projectionsmolded into the polyurethane facilitate installation of the tube.

air entering through the ceiling and exhaustingthrough specially constructed walls. Laminar-flowclean hoods are installed at work stations wherethe most critical operations are performed. Thedust count at these stations is never more than10 particles per cubic foot in normal use.

The installation also has separate vestibules inwhich shoes are machine brushed and specialclothes donned. Particular attention was given tothe construction of the ceiling and floors so as topermit easy maintenance. To ensure special clean-liness in critical areas such as the photo-resistrooms, these rooms are held at a higher pressurethan others. Services such as gas and water alsoreceive special treatment: Before entering therooms, the gases are filtered and dried, and thewater (deionized) is double filtered.

In addition to technical people from WesternElectric and Bell Labs, the installation has manyWestern Electric operating personnel. Their pres-ence affords them early exposure to the new tech-nologies, which is important, since they will laterserve as the nucleus of the manufacturing force.The advantages of this arrangement are two-fold: The Western people have a chance to pre-pare for manufacture at an early stage, and theBell Labs people have a chance to benefit fromtheir advice. The result is that many of the de-velopment tools, fixtures, and machines can beeasily incorporated into future manufacturingfacilities.

A pulsed ruby laser inside this "black box" en-sures precise alignment of the camera tube'sbeam-stripper-the electrode that trims the elec-tron beam to a diameter of 0.003 inch. After thebeam stripper is aligned with other electrodes,the laser bores a 0.003-inch hole through it. BobSell, on assignment to the Reading Laboratoryfrom the Western Electric Company, is shownloading an electron-gun structure into the unit.He will use the television monitor to aim the beam.

Planning maintenance procedures for Picturephone service requires a considerable de-gree of foresight. Practices suitable for only a few customers initially will still have tobe viable in the future when video service is as widespread as telephone service is today.

Maintenance-Keeping the System in Trim

T ODAY, as PICTUREPHONE® service makes itsfirst appearance, we are relatively unencum-

bered with previous maintenance procedures. Thisgives us a unique opportunity to plan overallmaintenance arrangements before the service isintroduced-although, obviously, new arrange-ments should fit in with existing ones as much aspossible.

With this freedom, however, comes the challengeto plan ahead so that maintenance arrangementsinitially required for only a relatively few custom-ers in one or two cities will still be valid or adapt-able when Picturephone service is as widelyused as the telephone is today. This article de-scribes how the Bell system is preparing to meetthe challenge. Of necessity, our present emphasisis on planning rather than on accomplishment.Much of the circuit and equipment design is stillin progress, and it is impossible to work out allthe details of a maintenance plan until the de-tailed nature of equipment and circuitry is knownand some operating experience is gained.

The starting point for planning maintenance

May/June 1969

A. E. Spencer

arrangements for new equipment is to considerpresent practice. Maintaining the telephone planttoday is a complex job that requires the effortsof a large number of the Bell System's employ-ees. Their efforts are directed at detecting, locat-ing, and repairing troubles in three generalareas: (1) loops and customer equipment, includ-ing PBX's, (2) interoffice trunks, and (3) switch-ing offices. For performing these tasks, mainte-nance personnel have a variety of test equipmentat their disposal, ranging from simple meters tohighly sophisticated equipment capable of mak-ing many complex tests automatically.

Yet, in spite of all this test equipment, ourability to detect and locate troubles is not alwayssatisfactory. All too often, we are not aware oftrouble until the customer reports it. And all toooften, a repairman must be sent into the field tolocate that trouble. He, in turn, may have to workwith another man in the central office-all ofwhich is time-consuming and expensive.

In planning maintenance for the Picturephonesystem, we have tried to improve our ability to

Plans for station and loop testing include a sta-tion test line that will permit convenient testingof newly installed Picturephone sets and a local

test center (to the right, below) that will be ableto perform a number of tests on all equalizers be-tween Picturephone sets and the central office.

detect, locate, and repair troubles while keepingoverall costs down. Similarly, we have tried tointegrate maintenance for the Picturephone sys-tem with existing telephone maintenance prac-tices. For the voice channels of the Picturephonesystem (see the diagram at top of this page), thestation and loop testing arrangements are iden-tical to those being used today for conventionaltelephone service. For the video channels, the ar-rangements are similar but are considerably im-proved in that tests made at maintenance centersand local test desks are expected to be much moreeffective in locating troubles.

In new installations, an installer will be ableto make a number of simple but valuable testswith a "test line" (shown to the right of thevideo switch in the block diagram). After com-pleting an installation, he can dial the video pre-fix (#), followed by a three-digit test accesscode and the last four digits of the line he hasinstalled. The central office will then connect thenew line to the test line, and the installer willhear a tone.' Now, if he flashes his switchhookand hangs up, the central office will transmit thespecial Picturephone ringing signal to test thisaspect of the new set's operation. When the in-staller answers, he will be able to make a numberof other tests, including some relatively simplevideo tests.

If the tests show that performance is not sat-isfactory, or if trouble develops later, it may benecessary to test the line from the new widebandlocal test desk. Here is where maintenance for

Picturephone service is expected to be signif-icantly better than present telephone maintenance.The tester can cause signals to be looped back atthe Picturephone set and at all intermediateequalizers in the loop. Both ac and do tests can bemade of the equalizers. Since the equalizers arepowered over the loop and draw relatively fixedcurrents, simple voltage and current measure-ments can be made to locate open or short cir-cuits on the line within an equalizer section.It will also be possible to send a low-frequencysignal out over the video portion of the loop tocontrol an equalizer in such a way that the signalwill be returned from it if the equalizer is work-ing. It will then be possible to loop similar sig-nals back through the second and third equal-izers, if there are any. This procedure shouldmake it possible to locate faulty equalizers beforedispatching a repairman.

Following successful completion of these simpletests, it will be possible to transmit a video testpattern to the video set. If the set is on hook, thevideo signal will be returned to the test positionthrough the loop-back feature at the station.Measurements of received signal level, quality,and other factors will then permit further troubleanalysis.

The arrangements for interoffice trunks aredifferent. (See the diagram on page 185.) Sincethe initial number of interoffice Picturephonetrunks will probably be quite low, the trunk testfacilities will be manual at first, and not auto-matic. For very small offices, all trunk mainte-

182 Bell Laboratories Record

nance may be done with maintenance center fa-cilities, and no wideband trunk test positionshould be required. As service grows, however, awideband trunk test position may be installed,and, ultimately, automatic test facilities for videotrunks will probably be developed to complementthose now being designed for audio trunks. Thetest facilities will have appropriate access tothe central office switching network so that allparts of tandem and intertoll trunks may betested.

In general, the tests that can be made on trunksthat carry analog signals will be similar to thetests that can be made on loops. Although the de-tails of equalizer designs will be different, therewill be similar facilities for locating troubleswithin any section between two equalizers.

In No. 5 crossbar, conventional jack access toall audio trunk pairs will be provided for testing.Besides allowing a testman to make normal trans-mission tests, these jacks will give him direct ac-cess to signaling leads as well as a way of makingthe facility busy simply by inserting a suitableplug. Insertion of the plug will also make thecorresponding video facility busy. With ESS, themore convenient switched access, rather thanjack access, will be provided to test both audioand video trunks.

Today, we have a series of test trunk termi-nations in distant offices that can be reached ona dial-up basis for conventional audio trunk test-ing. For Picturephone service, we will have anequivalent series for video trunk testing. For ex-ample, one type of test trunk will terminate thereceive direction of the video facility in a match-ing impedance and will generate a short burstof 1-kHz tone over the transmit direction as wellas over the audio channel. After this, the trans-mit direction of both the video and audio facil-ities will again be terminated in a matching im-pedance.

Another type of test trunk will have facilitiesfor Picturephone service and two-man testingbetween test-boards using a wide variety of testequipment. A third type of trunk will terminate

The new wideband trunk test positions now be-ing planned for the Picturephone system may looklike this artist's rendering. Located at centraloffices, the trunk-test positions will be equippedwith several test instruments new to telephonemaintenance. Among these are wideband oscillo-scopes for analyzing video signals and "echo-rating" test sets for measuring echo in trunks.

the receive direction and supply a steady source of 1-kHz tone over both the video and audio facilities in the transmitdirection. After about 20 seconds, the test tone will be removed, and the receive side of the trunk will be connected tothe transmit side. Still another type of trunk will permit signaling tests by cycling, the trunk through on-hook and off-hook conditions.

A major difference between trunk and loop testing is that trunk testing arrangements will have to include tests of digitalfacilities, whereas loop testing arrangements will not. Codecs (devices for coding and decoding video signals in digitalform) will be used only with trunks, and provisions will have to be made for testing them. In general, the basic test of acodec will involve a loop-back in which a test signal is first coded in the coder and then connected back to the decoder.At the decoder, the test signal will be decoded for comparison with the input signal. For such testing, the codec willmost likely be controlled over a direct path from the maintenance center and the wideband trunk test position-at least,initially. As the use of digital facilities increases, this procedure will probably change.

Maintenance of the switching equipment itself will generally follow procedures already in use. For example, in the caseof No. 5 crossbar, trouble record indications will be received from alarms and trouble cards just as they are today. Inthe case of No. 1 ESS, of course, the maintenance control console and maintenance teletypewriter will be the focus of atestman's activities. In both cases, he will follow normal routines to locate and repair the trouble.

As a trouble detection technique, not only in switching equipment but in transmission facilities as well,an ac continuitytest of the video path will- be made prior to every call. This test will not only help in the detection and location oftroubles; but will also improve the level of service received by customers. Implementing the overall maintenance plans

Artist's rendering of what a local test desk for the Picturephonesystem might look like. Such "desks will be installed in centralizedlocations to test Picturephone lines throughout a city.

will require some new kinds of test equipment,although much of the equipment in use todaywill still be usable. For example, a low-frequencytransmission measuring set will give a roughidea of how a video facility is performing. Butit will be necessary to go beyond this and createa video-frequency transmission measuring set.Similarly, wideband versions of such instrumentsas noise-measuring sets and variable frequencyoscillators will be needed. Most of these instru-ments are similar in kind to voice-frequencyequipment; however, some new instruments willbe peculiar to the Picturephone system. Theseinclude a video-image generator to serve as asource of video test signals; a video monitor forobserving signals; an oscilloscope for observingsignal waveforms; and a delay measuring set, or"echo-rating" set as it is sometimes called.

"Echo-rating" is a new concept. It is deter-mined for a given facility by first measuring thepower in any echoes reflected from impedancediscontinuities in that facility. The powers of thevarious echoes are then weighted, with the great-est weight being assigned to the echoes that aremost delayed from the desired signal. The ratio ofthe sum of weighted echo powers to the power ofthe desired signal is called the echo rating. Theecho-rating test set will perform the rather com-plex functions of measuring, comparing, andweighting echoes, and will then display the re-sult. After measuring individual sections of anoverall facility or connection with an echo-ratingset, it will be relatively simple to determine whichsections are the source of excessive echo signals.

The echo-rating test set will be extremely use-ful in providing high-quality pictures. Alongwith all the other test equipment mentioned, itis part of an overall plan to assure customers oftrouble-free service as well.

May/June 1969

Block diagram of the maintenance arrangements planned forinteroffice trunks in the No. 5 crossbar system. Audio facilitiesare shown in black, and video facilities are shown in grail. Sincetandem and intertoll trunks terminate on both sides of the cen-tral office switching network (indicated here by the video andaudio switches), test facilities must also have similar dual ac-cess. Maintenance arrangements will include equipment for test-ing wideband video signals and digital facilities such as thecodecs that code (and decode) video signals into digital form.

185

Tomorrow

THIS SPECIAL ISSUE of the Bell Laboratories

RECORD shows what we are doing to provide PIC-TUREPHONE® service. As the service becomes avail-able to more and more people, new features willbe developed to increase its versatility. For ex-ample, we are working on a method that will al-low businessmen to see and read high-resolutioni mages of drawings, sales literature, reports, andthe like. By using a slow-scan mode, which per-mits high resolution with no increase in band-width (but at the sacrifice of being able to followrapid motion), such graphics service can be pro-

vided over the Picturephone network. Hard copyprintout of picture images could be an addedfeature in such a service.

A way to allow people to hold conferences viathree or more Picturephone sets is another es-sential need for business customers. And here too,

work is in progress to add such a conferencingfeature at the earliest practicable time. A voice-

operated Picturephone conference system is nowbeing evaluated in the laboratory. The system au-tomatically distributes the Picturephone signalfrom the person speaking to all other listeners;the speaker sees the person who spoke last. Al-though the system is intended primarily for face-to-face conferencing, it would not be limited tothis use. It could be used for management presen-tations that include charts and graphs, for ex-ample, or for product or other pictorial displays.Another possibility is that information generatedby a computer might be displayed on the sets ofall conferees. In this case, each conferee could in-

teract with the computer through his TOUCH-TONE® dial.

As you have seen in this issue, a computer dis-play capability has already been incorporated intoPicturephone service, and this capability is beingfield-tested in the product trial with WestinghouseElectric Corporation. Some future uses of the

Picturephone set as a display device may well in-clude interactive computer graphics using a light-pen or special keyboard.

Many of the features mentioned in this issueare being considered with a view toward improv-ing the utility of Picturephone service for busi-ness use. Picturephone services for other uses arebeing considered as well. For example, we'll belooking at special Picturephone sets for specificapplications. The present Mod II set, designedprimarily for desk-top application, will ultimatelybe joined by other models, such as wall models forresidential use. And it is not difficult to foreseethe eventual growth of booth service.

Color Picturephone service is an obvious sequelto our present development and hopefully com-patible with it. Broadcast color television sug-gests a general pattern for a system of color Pic-turephone. However, the camera as used in color

television today does not seem to be adaptable forPicturephone. A Picturephone camera (1) mustbe able to operate satisfactorily under light ofwidely varying intensity and spectral content, (2)should require little or no adjustment by the cus-

tomer, (3) should maintain its standards withoutservice adjustments for periods of many years,

186 Bell Laboratories Record

and (4) must especially give a good rendition offacial skin tones. For these reasons, research andexploratory development at Bell Laboratories arenow concentrating on color camera systems thatare simple, stable, and will work reliably in thehome or office environment.

Color perception by human beings has manysubjective characteristics. The colors we think wesee are often very different from the true colorof light reflected by objects in all the various con-ditions of illumination. Fundamental research oncolor perception at Bell Laboratories will, wehope, yield greater basic understanding of thiscomplex phenomenon.

Looking even further into the future, we canimagine 3-D Picturephone images, or arrange-ments whereby equipment could be attached todeliver a print of whatever picture is on thescreen. It is easy to speculate about these andother applications, but it is not so easy to findanswers to the many scientific and engineeringquestions they imply. We nevertheless intend toinvestigate all promising approaches, so that thetechnology will be ready whenever the needs andthe economics are favorable to development.

In addition to the provision of new services wemust, of course, search constantly for ways tomake Picturephone service cheaper. Further ex-ploitation of integrated circuits will doubtless con-tribute significantly in that direction. New cablesfor the loop plant will make broadband transmis-sion easier to accomplish. Methods of "bandwidthreduction," in which only those elements of a pic-ture are transmitted which change from frame toframe, also look promising. Such a system hasbeen demonstrated by our research people. Whilethe terminal equipment needed to accomplish theelimination of redundancy is, in its present form,rather complicated, we are hoping that eventuallyit can be made cheap enough to yield an overallsavings in the cost of transmission.

The coming of the Picturephone age will repre-sent the maturing of a 1-MHz switched network.Fortunately, as described in this issue, this net-work can start as an "adjunct" to the networknow used for telephone services. It will use tele-phone loops, trunks, and switching machines withonly relatively moderate changes and additions.When the day comes, however, that Picturephonerepresents a substantial part of our communica-tion services, then its effect on the Bell Systemplant will be profound. To get from now to thenis an exciting challenge to all parts of the BellSystem. To meet it and succeed will require hu-man energy, capital funds, imagination, and wis-dom in abundance.

-J.P.M.

May/June 1969

Research currently in progress at Bell Laboratories will leadeventually to the development of Picturephone service in color.

A voice-operated conference system, now being developed, willincrease the utility of Picturephone for business customers.

THE AUTHORS

Irwin Dorros (PICTUREPHONE®)is Director of the Network Plan-ning Center. His responsibilitiesinclude the systems engineeringaspects of the Picturephone sys-

Claude G. Davis (Getting the Pic-ture) is Director of the TelephoneLaboratory at Bell Labs' Holmdel,N. J., location. His organizationdevelops new kinds of telephoneinstruments for use by customers;the Mod II Picturephone set wasone of its products.

Mr. Davis joined Bell Labs in1950, and his early work concerneddevelopment of exchange and tollcable. Later he specialized in de-velopment of transmission sys-tems and worked on Pulse CodeModulation (PCM) and Time As-signment Speech Interpolation( TASI). In 1961 he became Headof a department responsible forrepeater design and data analysisin the TELSTAR® project, the Bell

188

I. Dorros

tem, the centralization and auto-mation of network operations, andplanning for the toll network.

Mr. Dorros joined Bell Labs in1956. His first work was on devel-

System's experimental communi-cations satellite program. He be-came Head of a department de-veloping customer radio systemsin 1962, and Head of the Sub-scriber Loop Systems Departmentin 1964. He was appointed Direc-tor of the Subscriber Systems Lab-oratory in 1966, and assumed hispresent position last year.

Born in Beech Grove, Indiana,Mr. Davis graduated from highschool in Ashtabula, Ohio. He re-ceived the B.S. degree in electricalengineering from Case Institute ofTechnology in 1950, and the M.S.degree in math from Stevens In-stitute of Technology in 1960. Mr.Davis is a member of the IEEEand Eta Kappa Nu.

C. G. Davis

oping various transistor circuitsfor the early electronic switchingsystems. In 1960 he became Su-pervisor of a group engaged in de-signing data communicationequipment for use on ordinary tele-phone facilities. He was namedHead of the Pulse Code Modula-tion Repeater Department in 1962,where his duties involved design-ing a transcontinental system fortransmitting all kinds of informa-tion by means of streams of high-speed pulses. Mr. Dorros assumedhis present post in 1966.

Mr. Dorros attended the Massa-chusetts Institute of Technology,where he was awarded the S.B.and S.M. degrees in electrical en-gineering in 1956. He received theEng. Sc. D. (Doctor of Engineer-ing Science) degree from Colum-bia University in 1962. Mr. Dorrosis a member of the IEEE, EtaKappa Nu, Tau Beta Pi, andSigma Xi.

James R. Harris (co-author VideoService for Business) is Directorof the Customer Switching Engi-neering Center, which is responsi-ble for engineering studies of PBXand key telephone systems, someaspects of coin telephone serviceimprovement, speech processing,customer switching systems, andplanning of new network arrange-ment for government communica-tions.

Upon joining Bell Labs in 1942Mr. Harris developed airborne ra-diotelephone and navigation sets.In 1950 he joined a group develop-ing transistors and digital tran-sistor circuits. He joined the TRA-DIC (Transistor Airborne DigitalComputer) project when it wasformed in 1951. In 1956 Mr. Har-ris was appointed Head of a de-partment concerned with data pro-cessing. Two years later he turnedto exploratory work on data com-munications. He was appointed

Robert D. Williams (co-authorVideo Service for Business) isDirector of the Customer Tele-phone Systems Laboratory. He isresponsible for development ofPBX's, key telephone systems,telephone answering systems, au-tomatic call distributors, and pri-vate telephone systems.

Mr. Williams came to Bell Labsin 1946 and joined the trial instal-lation group, where he worked onthe first installation of the No. 5crossbar switching system. He waslater concerned with developingthe 740E and 756A PBX's andspecial systems such as recordedtelephone-dictation equipment andthe Civil Air Raid Warning Sys-tem. He also worked on develop-ing the No. 101 ESS, an electronicPBX. Mr. Williams became Headof the PBX Development Depart-ment in 1961, and took over hispresent post last year. He will be-

May/June 1969

Director of the Data Systems En-gineering Center in 1961, and tookover his present position in 1965.

Before coming to Bell Labs,Mr. Harris was with the Chesa-peake and Potomac TelephoneCompany, first as a toll central of-fice repairman and later in equip-ment engineering.

Mr. Harris received the B.S. de-gree in physics from the Univer-sity of Richmond in 1941, and theM.E.E. degree from the Polytech-nic Institute of Brooklyn in 1948.He is a member of the IEEE anda past member of the Administra-tive Committee of the Institute'sGroup on Electronic Computers.He is also a member of Phi BetaKappa and Sigma Xi.

come Director of a new Bell Labsswitching development center tobe built in Denver, Colorado, wherehe will be responsible for the de-velopment of telephone communi-cation facilities installed by BellSystem companies on customers'premises, such as key systems andPBX's.

Mr. Williams received the B.S.degree in electrical engineeringfrom the Case School of AppliedScience in 1945. He is a memberof the IEEE, Tau Beta Pi, EtaKappa Nu, Theta Tau, and PiDelta Epsilon.

R. D. Williams

189

J. R. Harris

F. A. Korn

Frank A. Korn (co-author Choos-ing the Route) is Director of theLocal Crossbar Switching Labora-tory at Bell Labs' location in theWestern Electric Company Worksat Columbus, Ohio. He has beendeeply involved with No. 5 cross-bar switching since its inceptionin 1945, and his present responsi-bilities include all developmentwork being done to keep this"workhorse" system up to dateand extend its usefulness.

Mr. Korn has been with BellLabs since its incorporation in1925. He came to the Bell Systemin 1920 as a member of the Engi-neering Department of the West-ern Electric Company, which be-came BTL five years later. Eversince then his work has concerneddial switching systems. He firstworked on the panel and step-by-step systems. In 1933 he joined agroup responsible for fundamentalplanning of crossbar switchingsystems, including No. 1 crossbar,crossbar tandem, and No. 4 toll.During the war his efforts werediverted to military projects, in-cluding the design of airborne nav-igation radar and bombing sys-tems.

For a short time after the war

Alistair E. Ritchie (co-authorChoosing the Route) is Directorof the Toll Switching EngineeringCenter, which is responsible forengineering studies of toll switch-ing systems.

Mr. Ritchie joined Bell Labs in1937 as a member of the testinglaboratory in the switching devel-opment organization. In this ca-pacity he worked on the testingprogram for the original No. 1and No. 4 crossbar systems. Afterinstructing in Bell Labs' School forWar Training, Mr. Ritchie joineda group planning and teachingcourses in design of switching cir-cuits. He taught a graduate coursein the principles and design ofswitching circuits at MIT in 1950-1951. Later he was concerned withthe planning of traffic measuringequipment, and in 1953 was ap-

A. E. Ritchie

Mr. Korn was responsible for ex-ploratory development of a newdial switching system using elec-tronic devices and intended for usein small communities. In 1947 heassumed responsibility for all cir-cuit development of a new dialswitching system-No. 5 crossbar.He was named Director of Switch-ing Systems Development in 1952;with responsibility for develop-ment work on all local dial centraloffices and PBX's. When the Co-lumbus Laboratory was organizedin 1958, Mr. Korn was appointedits Director and charged with get-ting the new facility going. Hetook over his present post in 1963when the Columbus facility wasexpanded. Mr. Korn was a mem-ber of the RECORD's EditorialBoard from 1952 to 1959.

Active in community affairs, Mr.Korn is a member of the Colum-bus Area Chamber of Commerce.He is also a member of the Ad-visory Committee to the ColumbusArea Technical School, the Advis-ory Board of the St. Ann's Hos-pital in Columbus, and the Boardof Directors of the Ohio StateUniversity Research Foundation.He was named a Fellow of theIEEE last year.

pointed Special Systems Engineerin charge of certain military com-munications and government pro-jects. He became Systems Plan-ning Engineer in 1955 and wasengaged in studies of line concen-trators and the original applica-tion of TOUCH-TONE® dialing. In1958 he became Director of Switch-ing Systems Engineering, wherehe was responsible for engineer-ing planning of electro/mechanicalswitching systems, and in 1965 heassumed his present position.

Mr. Ritchie received the B.A.and M.A. degrees in physics in1935 and 1937, respectively, fromDartmouth College. He is a seniormember of the IEEE. He is co-author, with W. Keister and S.H. Washburn, of The Design ofSwitching Circuits, which is astandard text on the subject.

Bell Laboratories Record

David W. Nast (co-author Trans-mission Across Town or Acrossthe Country) is Director of theTransmission Facilities PlanningCenter. His responsibilities includeengineering planning of wire, ra-dio, and satellite transmission fa-cilities.

Since joining Bell Labs in 1953Mr. Nast has specialized in sys-tems engineering in such fields asexchange transmisssion, pulsetransmission studies, and wide-band data transmission. He wasappointed Head of the BroadbandSystems Studies Department in1964. In 1966 he became Head ofthe PICTUREPHONE® EngineeringDepartment, responsible for thetechnical planning for Picture-phone service. He moved to hispresent position last year.

Mr. Nast received the B.E.E. de-gree from Cornell University in1953, and the M.S. degree in elec-trical engineering from Newark

May/June 1969

D. W. Nast

College of Engineering in 1957.He received the Professional Elec-trical Engineer's degree from Co-lumbia in 1964. He is a memberof the IEEE, Eta Kappa Nu, PhiKappa Phi, and Tau Beta Pi.

Irwin Welber (co-author Trans-mission Across Town or Acrossthe Country) is Director of theOverseas and Microwave Trans-mission Laboratory. His organi-zation is responsible for thedevelopment of transoceanic sub-marine cable systems, waveguidetransmission, high-frequency ra-dio, and digital transmission onexisting radio systems.

Since coming to Bell Labs in1950, Mr. Welber has specializedin work on transmission systems.

I. Welber

His early assignments includedcircuit design, systems analysis,and field testing of an automaticprotection system for microwaveradio. He later did system analy-sis and design work on the TimeAssignment Speech Interpolation(TASI) system. In 1960 he wasappointed Head of the Ground Sta-tion Design Department, in whichpost he was responsible for over-all systems analysis, ground com-munication equipment, and tech-nical planning with foreignparticipants on project TELSTAR®.

During the early Telstar experi-ments he was in charge of oper-ations at the ground station inAndover, Maine. He moved up tohis present position in 1965.

Mr. Welber received the B.S. de-gree in electrical engineering fromUnion College in 1948 and hisM.E.E. from Rensselaer Polytech-nic Institute in 1950. He is a mem-ber of the IEEE and Sigma Xi.

Frederick T. Andrews, Jr. (co-author Connecting the Customer)is Director of the Loop SystemsLaboratory. He is responsible fordevelopment work on the "loops"that connect customers' telephonesto their local switching offices.

Upon joining Bell Labs in 1948Mr. Andrews worked in switchingresearch on line concentrators andmagnetic logic devices, and in 1955he became a Supervisor in trans-mission systems development. En-gaged in exploratory developmentof Pulse Code Modulation (PCM)transmission, he was responsiblefor planning and circuit develop-ment of portions of the terminalsand line repeaters for the experi-mental forerunner of the first com-mercial PCM system. In 1958 hebecame Head of the TransmissionSystems Engineering Department,and was responsible for transmis-sion objectives and maintenance inthe telephone and data fields. Hewas appointed Director of theTransmission Systems Engineer-ing Center in 1962, and Directorof the Military CommunicationsSystems Engineering Center in1966. He took over his present po-sition last year.

Mr. Andrews received the B.S.degree in electrical engineeringfrom Pennsylvania State Univers-ity in 1948, was a member of thefirst group to enroll in Bell Lab-oratories' Communications Devel-opment Training Program, andhas done graduate work in math-ematics at Rutgers University. Heis active in the IEEE as a mem-ber of the Wire CommunicationsCommittee, where he heads a taskforce on telephone measurement.As Vice Chairman of a StudyGroup of the Committee Consul-tatif International Telegraphiqueand Telephonique, he is concernedwith transmission objectives andlocal transmission standards as re-lated to planning the world-widecommercial telephone network.

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F. T. Andrews, Jr.

Henry Z. Hardaway (co-authorConnecting the Customer) is Di-rector of the Exchange Plant Sys-tems Engineering Center. He di-rects engineering studies of newcommunications cable and wire fa-cilities, inductive interference, andoutside plant maintenance. In-cluded is the responsibility for ex-change transmission requirements,station set requirements, specialservices requirements, and studiesof the application of electronics tothe exchange plant. He is also re-sponsible for studies leading tothe application of electronic com-puter techniques as tools for BellSystem operating telephone com-pany engineers to use in solvingtheir engineering and planningproblems in the exchange plant.

Upon joining Bell Labs in 1942Mr. Hardaway engaged in equip-ment design work on various mil-itary projects, including airborneand submarine radar equipmentand navigation equipment. In 1955he became Head of a departmentin outside plant systems engineer-ing. In 1963 he was appointed Di-rector of Outside Plant SystemsEngineering, directing the plan-ning of new cable and wire facil-ities for the Bell System and con-ducting other studies. Last yearhe moved to his present post.

Mr. Hardaway received the B.S.degree in mechanical engineeringfrom the State University of Iowain 1940. He is a member of theAmerican Society of MechanicalEngineers and the American Ord-nance Association.

H. Z. Hardaway

Bell Laboratories Record

Sture O. Ekstrand (Devices-The Hardware of Progress) is Di-rector of the Semiconductor De-vice and Electron Tube Labora-tory at Reading, Pennsylvania. Heis responsible for development ofsemiconductor devices such as di-odes and microwave transistors,silicon integrated circuits, and elec-tron tubes.

After coming to Bell Labs in1926 Mr. Ekstrand specialized inthe design of mechanical struc-tures for test fixtures and ma-chines, as well as various kinds oftelephone and recording appara-tus. In 1935 he moved to the Elec-tron Tube Laboratory, where heengaged in development of alltypes of electron tubes for bothBell System and military applica-tions. In 1941 and 1942 he was aproduction engineer with the West-ern Electric Company; then he re-turned to BTL and supervised agroup responsible for design and

Albert E. Spencer, Jr. (Mainte-nance-Keeping The System InTrim) is Director of the LocalSwitching Engineering Center. Hisorganization conducts studies inthe local switching field and es-tablishes objectives and require-ments for local switching systems.

Mr. Spencer joined Bell Labs in1951. After assignments in the de-sign of circuits for transmissionsystems and a secure voice com-munication system, he supervisedinitial design work on the time-division switch unit for the No.101 Electronic Switching System.

May/June 1969

processing of electron tubes. From1945 to 1955 Mr. Ekstrand super-vised electrical and mechanical de-velopment of certain types of elec-tron tubes, and was a consultantto BTL groups doing militarywork. In 1955 he became Head ofa department at Bell Labs' loca-tion in Allentown, Pa., where hewas responsible for developingcertain chemical processes, struc-tures for semiconductor devicesand electron tubes, and for appliedmechanics studies. He moved tothe Reading Laboratory in 1957,and became its Director in 1960.

Mr. Ekstrand received the B.S.degree in electrical engineeringfrom Cooper Union in 1935. He isa member of AAAS and a Fellowof the IEEE. He is also a mem-ber of the Joint Electron DeviceEngineering Council, the Elec-tronic Industries Association, andthe United States of AmericaStandards Institute.

He later supervised one of severalgroups responsible for planninga global military communicationsystem. In 1962 he was appointedHead of the Data Switching Engi-neering Department, responsiblefor objectives and requirementsfor a store-and-forward data com-munication system. He has heldhis present post since 1965.

Mr. Spencer received the B.S.degree in electrical engineeringfrom the Drexel Institute of Tech-nology in 1951. He is a member ofthe IEEE, the AAAS, Tau BetaPi, and Eta Kappa Nu.

A. E. Spencer, Jr.

S. O. Ekstrand

1 93