Data transmission in printing & publishing: A Survey of the technical issues of on-line file transfer

Theses

Thesis/Dissertation Collections

1-1-1999

Data transmission in printing & publishing: A

Survey of the technical issues of on-line file transfer

John Altemueller

Follow this and additional works at:

http://scholarworks.rit.edu/theses

This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please [email protected].

Recommended Citation

by

John S. Altemueller

A thesissubmittedinpartial fulfillmentofthe requirementsforthe degree ofMasterofScience in the Schoolof

Printing

ManagementandSciences in theCollege

of

Imaging

Arts andSciencesofthe Rochester Instituteof

Technology

January

1999

Certificate

of

Approval

Master's

Thesis

This

IS

to certify that the Master's Thesis of

John S. Altemueller

name of student

With a major

In

Printing

Technology

has been approved by the Thesis Committee as satisfactory

for the thesis requirement for the Master of Science degree

at the convocation of

January18,

1999

Thesis Committee:

_~lsha_~~~

_

TIle.<i.< Advi.<or

Joseph

L.

Noga

~--Graduale Program Coortlitlalor

A Survey of the Technical Issues of On-Line File Transfer

I, John S. Altemueller

,hereby grant permission to

the Wallace Memorial Library of R.I.T to produce my thesis in whole or in part. Any

reproduction will not be for commercial use or profit.

ListofFigures v

Abstract vi

Chapter 1

Introduction p. 1

Endnotes p. 2

Chapter 2

Theoretical Basis p. 3

Endnotes p. 5

Chapter 3

ReviewoftheLiterature p. 6

Endnotes p. 24

Chapter 4

The Problem Statement p. 26

Chapter 5

Methodology

p. 27

Endnotes p. 33

Chapter6

The Results p. 34

Chapter7

Summary

& Conclusions p. 39

Appendix A p. 48

(Al)

Category

II Data

(Raw)

p. 49

(A2)

Category

II Charts

Fig. 2 Markettypes p. 50

Fig. 3 Connectiontypes p. 50

Fig. 4

Desktop

apps p. 51

Fig. 5 Formattypes p. 51

Fig. 6 Platformtypes p. 52

Fig. 7 Regionalmarkets p. 52

Fig. 8 Compressionsoftware p. 53

Fig. 9 Experience p. 53

Fig. 10 # filesreceived p. 54

Fig. 1 1 Transmissionerrors p. 55

Fig. 12 Protocolerrors p. 56

Fig. 13 Filesize errors p. 57

Fig. 14 Compressionerrors p. 58

Fig. 15 Postscripterrors p. 59

Fig. 16 PS errortypes p. 60

Fig. 17 Error detection p. 61

Fig. 18

Incompatibility

errors p. 62

Fig. 19File managementhours p. 63

Fig. 20 Fontssupported p. 63

Appendix B p. 64

Using

survey study

issuesof on-line pagefiletransferbasedon actual

industry

experience. Arandom sample of servicebureausthatsupport on-linefile transferwasdrawnfromthe 1995 Print

Resource Buyer's GuidepublishedintheDecember

28,

1994 issueof

Publishing

and Production Executive. Apilot _surveyofthe sample wasconducted inthe_{late spring}of

1995,

toestablish_{final methodology}and_{sampling techniques, followed}

by

a comprehensive_{survey in} the_{late summer/early fall. The survey} polledthe sample

population oversix technicalareas: transmission,filetransfer protocols,file formats ,file

size, Postscripterrorsand cross-platform

incompatibility

todeterminethe

key

factorsthat

significantly impactthe_efficiencyofthenetwork segment oftheiroperations,andthe

data foreachfactorwas tabulated

by

typefor hypothesis testing.The hypothesis posited

the

frequency

and _severityofPostscript errors asthe_primarynegativefactoronthe

efficiencyofon-line filetransfer. Inaddition,eightrelatedareas,internetconnection

methods,

desktop

applications,file

formats,

markets, file storage, computers,data

compression and experiencewiththe

technology

were surveyedtodetermine thelevelof experienceoftherespondentswiththis

technology

and the typesofhardwareand

software

they

employed.

The data fromthe_survey wereanalyzed and aChi-Square statisticaltest was performedto test thehypothesis. Thoughthe testresults didnot supportthe

hypothesis,

a substantial

body

ofdatawas compiled ontheactual experience withthe

technology

by

thesamplepopulationThe surveyofhardware andsoftwareshowed amixed suite of applications andplatforms.Macintoshcomputersremained theplatformofchoice,but Windows systems were well represented. Applicationsoftwarefor

desktop

_publishing came_{primarily from Quark}and Adobe. Themarkets servedwere also

diverse,

both in

types ofservicespurchasedand geographic location. Whilethe_primarymarkets are

regional,

forty

percentofthesample reported that

they

served anationalcustomerbase. Transmissionerrors werethemost reportedbottleneckforcustomerfiles deliveredvia

network, anindication that the_{carryingcapacity}orbandwidthofthenetworkis lessthan

seventy file

nextfiveyears. Thisperception couldhave asignificantimpactonfuture purchasing

patternsfornetwork_capability,

training

and relatedhardware and software.

Acomprehensive_summaryofthedataandtheconclusions drawn fromthe

analysisis setforthin Chapter 7 ofthisreport. Anextensive reviewofthe available literature isalsoincluded. This study is intendedto serve as abasis for future

Thegrowthofnetworkslike theInternetcreatesnewopportunities for printers

andtheir_customers,

leading

_manytoadopt anelectronicworkflow, thelogicalmarriage of electronic prepress , datatransmissionnetworksandthe

developing

capabilitiesof digitalprinting. As digitalprepress

technology

becomesthe norm,printer's clients are

consideringtheeconomicbenefitsof

transmitting

theirworktoservicebureaus inthe formofdigital data files.

( 1)

_{In theory,} complete pagefiles may be transmitted

directly

to_anyservicebureau inthe_countrywithon-linecapability,eliminating traditional

hardcopy

artwork ortextfiles aswellastheconstraints oftime and geography. The

portion ofthis environmentthatincludestheclient

file,

transmissionmedium, reception nodeand associated softwareisthe networksegment oftheworkflow.

(2)

Newcapabilities meannew _{opportunities,}buttherearenew variablesto control

andnew problemstoovercome. Thesuccessful transmissionofagiven pagefile

necessitatestheelectronic manipulation ofthedatato _successfullysend and receiveit. Afile mustbe

initially

prepared on a platform and softwarethatiscompatible with the

receiving bureau'sproduction equipment._{The file may}requiredatacompressionto facilitatestorage anddecreasetransmission_time, a significantexpensein thisnew

environment. Unlessadedicated digital line isused, thefile is transmitted,via_modem, over an_analogtelephonelinethat_{may be}subjecttosignalattenuation. Datatransferrates

may be painfully slow.

(3)

Toadd_{complication, today's}phone linesare oftena mix of analogand digitalmodes,with a signal

being

manipulated_manytimes

during

transmission.File Transfer

Protocols,

or

FTP,

mustbe inplace atthe_receivingendto

acceptthe transmitted

data,

withadequate storagein theservertomanagethe transmitted files.

(4)

Many

oftheseissues requiresystematicexaminationin thecontextofthe

network segment.

Whatfactors havethegreatest negativeimpact onthe_efficiencyofon-line

printing?Signal attenuationandtraffic onthenetwork, slowtransmission time, cross-platform

incompatibility,

and Postscripterrorsin clientfiles maycause significant

problems,butto whatdegree? Isone factor-Postscript

errors-more significantthan others?

(5)

Using

the_surveymethod, this_studyexaminedthis question,collecteddata on

1.

White,

Patrick "

Downto the

Wire",

Publishing

& Production Executive ,

March,

1995,

p.15-21

2. "Publisher'

s DiscovertheDigital

World",

The Seybold Reporton

Publishing

Systems,

22 April

1994,

v23nl5, p. 83-71

3.

Cuenca,

Mike"

HowtoGet It From HeretoThere"Folio,

June

15, 1994,

p. 35-36

4. "Anonymous FTP:

Frequently

AskedQuestions"

(on-line)

March,

1995,available:http://www.cis.ohiostate.edu/hypertext/faq

usenet/computer-security/anonymous-ftp-faq/faq.html

5.

Blessing,

Rose"

First,

Findthe Bottleneck"

Theresearch method chosen forthis _{study is}thedescriptivesurvey. Asa methodof

researchit has the

following

characteristics:

(1)

a). The data iscollected

by

observation.

b). Thepopulationofthe_studymust_{be carefullychosen,clearly}

defined,

and

specifically delimittedtoensurediscreteness.

c.) The datamustbe safeguardedfromtheeffects ofbias.

d.)

The datamustbeorganizedandpresented_{systematically for}valid conclusionsto be drawn fromthem.

To succeed,the _{survey is designed}to fullfill adiscreteresearchobjective,

focusing

onthoseareasvital to theinquiry. Thetoolsof_any successful _{survey include} thequestionnaire andthesample. A well-_{designedquestionnaire is relatively}

brief,

_but

adequatelyaddresses thegoals oftheresearchdesign.

Brevity

and_courtesyare

important,

sincetherecipientis

being

askedto surrender a period oftime toanswerthequestions.

The questionnaire should alsobe user-friendly,requiringa simple check orfill-in rather than a

long

_essayresponse. The samplepopulation mustbe carefullychosen anddefined

as thecorrecttargetforthesurvey.

(2)

To adequatelyaddressthequantitativeneedsofthestudy,theresearcher must

designthe questionnairetoelicitthe requireddata. Thescope ofthe

inquiry

mustbe

defined,

andthequestions focusedonthe

key

pointstobe investigated. Open

-ended questionshaveno place in the

design,

forthe_{data derived may be difficult}orimpossible toevaluate. For datatobequantifiablethequestionsmustrequire a specific_response,

basedon theobservedexperience ofthe subject. (3

)

Forexample:_{"How many}client

filesdo youreceiveeach week viaanonymous ftp?"

canbe answeredwith anumber-

10,

35,

200-_{anobjective response thatcanbeplotted on a graph and counted. Onthe other}

hand,

aquestionlike this: "Whatrole hason-line_printingplayedinyour

business?" may

being

evaluated, survey How many hasthebureauacceptedtransmitteddata

files?",

respondents who answered"lessthan 1"

wouldbe instructedto_{skip any}questions designed forthosewithayearor more of experience.

(4)

Questionnairesshouldbepretestedon a small sampleofthe targetpopulation. This is necessarytodetermine ifthequestionswillbe readilyunderstood

by

the target group, andifthequestionnaire, as _structured,will _actuallyelicitthe_{necessary data. A} pilot_{study may}alsoindicate anyproblemswiththe _samplingmethods or population definitions. To be_{effective, the} pilot_studyor pretest shouldbe considered an_on-going

process throughout the_{study design (5).}

Asample_{may be defined}and selectedin severalways,butmust representthe population

being

studied. Asamplepopulation mustbe random, representative,and sufficiently large.

(6)

Random samplingrequiresthateach memberofthe samplehavethe same_probabilityof

being

chosen as _anyother member.Forexample, each member ofthe samplepopulationis assigned a_number, and arandomnumber generatoris usedtoselect thesample members. Eachselectionis fromtheentire population.Thisensures a

representative_sample, and minimizes_samplingerror orbias. Theprocessisrepeated until therequired sample sizeisachieved. The largerthe samplethemore meaningfulthedata. Forstatisticalpurposes a sample sizeof atleast 30membersis requiredtouse themost powerful statisticaltools.

(7)

Theanalyticaldatacollected is tabulated,charted or_graphed, andtested

1.

Leedy,

Paul

D.,

Practical Research

, Fifth

Edition, 1993,

Macmillan

Publishing

Company,

New

York,

NY. p. 187

2.

Babbie,

Earl,

Survey

Research Methods, Second

Edition, 1990,

Wadsworth

Publishing

Co.,

Belmont CA. p. 56-60p. 127-128

3.

Leedy,

Paul

D.,

Practical Research , Fifth

Edition, 1993,

Macmillan

Publishing

Company,

New

York,

NY. p. 188- 189

4.

Babbie,

Earl ,

Survey

Research Methods , Second

Edition, 1990,

Wadsworth

Publishing

Co. , Belmont CA.p. 136 - 138

5.

Babbie,

Earl ,

Survey

ResearchMethods , Second

Edition, 1990,

Wadsworth

Publishing

Co. , Belmont CA. p. 220 - 225

6.

Babbie,

Earl ,

Survey

Research Methods , Second

Edition, 1990,

Wadsworth

Publishing

Co. , Belmont CA.p. 75 - 80

7.

Dowdy,

Shirley

&

Wearden,

Stanley

^Statisticsfor Research,

Second

Edition, 1991,

Wiley

&

Sons,

New

York,

NY.p. 9

8.

Babbie, Earl,

Survey

Research

Methods,

Second

Edition, 1990,

Wadsworth

Publishing

Co.,

BelmontCA. p. 31

All datacommunication systemshave threebasicphysicalcomponents:

atransmitter/receiver tosend and receivethe

data,

adevicetomanipulatethedatasignal,

and atransmissionmedium.Thereare severaltypesoftransmissionandreceptionde

vices.

Printers,

_terminals, personalcomputers andimagesetterscan allbeconfiguredto

functionas part of acommunicationsystem.

Analog

anddigital lines differ inthe_way

data isencodedfortransmission. _{For analog data}theamplitudeor

frequency

ofthe signal

is modulatedto_carrytheinformation. Digital data is containedin

binary

digits,

orbits ,

represented

by

0or 1-theswitchiseither "on"

or "off"- without_anyextraneousnoise

orinterference. Digitalnetworks permitthedevelopmentof_{extremely highcapacity,} high

speedtransmissionwithaminimum error rate. Signalmanipulationdevices are

represented

by

modems. Amodemconverts adigitalsignalfrom anoutput

device,

_saya

personal_computer,and modulates thatsignalfortransmissionover an _analogtelephone

line. Asecond modemat the_receivingenddemodulatesthesignalback into digital form

toan output

device,

like animage setter.This signalis sent over someformof

transmission medium,

broadcasting

overtheairwaves oron a cablenetworkofcopperor

opticalfiber.

(1)

Electronictransmissionsrequire procedures,knownasprotocols,toinitiateand

maintain communications. Oneprotocol isconcerned withthe_{way data}moves

directionally

overthe line. Threemethods_{generally in} useare_simplex, half-duplexand

full-duplex. Simplextransmissionis

one-wayonly.Datamovesfromaninput devicetoa

processing device inonedirection. The bestexample istheinputterminal_{designed only}

tosenddatatoamainframe computer.This modeis seldomused incommunications.

Half- duplextransmission allowstwo

waycommunication, but only in onedirectionata

time. Amessageis sentin one

direction,

received, andthesendermustwaitfor a_reply

andforthedirectiontorealignbefore sendingmoredata. This

lag

in directional

communication iscalledturnaround time. Whilethis_{limitation may be}acceptablefor

voicecommunication,itpresents obvioushandicaps for datacommunications. Afull -duplextransmissionpermitstwo _waysimultaneous communications, thepreferred mode

point-to-point conventionallines are_{usually four}wire. Conventional

lines,

designed

originally forvoice_{communication,} have beenadaptedto_{carry data}

by

theaddition of

another pair of wires dedicatedto datatraffic. Thesecombinedvoice/datanetworks _using

analog linesarethepresent

industry

standard, buttherapiddevelopment ofdigitalnets, especially for

long

range, high-speeddatacommunications, promisean enormous increase in capacityoverthe traditional systems.

Moderntelephonenetworksreach_{nearly every}corneroftheworld.This ready

made_{pathway is} anobviouschoicefor datacommunication aswellasvoicetraffic.

Data,

whether_text,

images,

or_telemetry, cantravel thesamelines. Aphone line may be

pointtopoint ormultipoint,

depending

onitsuse. Apointtopointlineis dedicated from

one point oftransmission to anotherpointofreception. _{The line may be}purchasedor

leased fortheexclusiveuseofthesubscriber.Whilethis optionisconvenient thereis

nocompetitionwith othertrafficand_{line security is}easiertomaintain it is alsocostly. A dedicated_{line may be}three tofourtimesmore expensive thana regular public access line. Amultipoint systempermits a number oftransmissiondevicestousethe sameline

throughtheuse of amultiplexerthatallows each deviceto accessthe systemon atime

sharing

basis,

reducingtheexpense.

Theneedfor highspeed networkshas grownacutewiththeexplosive growth in

thedemand for information in general,andthe developmentof computerized pre-press

equipment andsoftwareinthe_printingand_publishing

industry

inparticular. The carrying capacityof anetwork, orbandwidth,isexpressedin Hertz

(H),

therangeoffrequencies

that_{may be} usedfortransmission. Therateoftransmission isexpressedin bitsper

second,orbit/s. Eight bitsare grouped intoa

byte,

andthemodulation rateofthe

transmissionisexpressedinbaud. Thetransmission speed requirementfora networkis a functionofinformation coding.Forexample, afour-colorpageforatypicalmagazine format mayconsume 500Kbytesof memory._{To economically}transmit thispage a

minimumlOOMbit/softransmissionthroughputis required.

Terrestrial networks_{may be}represented

by

privatedigital lines like the56Kbps

assembly 64Kbps working in to transmitvast amountsofdigital information. Apopular variation istheFractional Tl

network, forusers who require rapiddedicated digital lineservice,butnotthefull

bandwidthofa regularTl network.Thesubscriber pays _{only for}theportion ofthe

bandwidth actuallyused,realizing substantialsavings.Theline speedof64Kbps is

becoming

standardin foreignmarkets aswell. Itistherate of choice for

Tl,

theEuropean

El,

and

ISDN,

the Integrated Services Digital

Network,

adigital communication network

technology

thatpermitstheserviceproviderstoofferawide_arrayofservices over a

singleset ofphonelines. Otherservices include Switched

56,

a

dial-up

56Kbps digital

linkavailable frommostlarge domesticphone companies.

(3)

It has beennotedthat dedicatedprivatelines frompoint-to-_pointareused

primarily

by

clientswho can

justify

thecostbecause

they

havetheneed to transmitlarge

amounts ofdataover a secureline. There is no limitationonthekindofdatatransmitted

as

long

asthe line iscapable of_carryingthe traffic.(4 )The_{necessity for dedicated}private

lines wilbe furtherreduced

by

frame relayservices, designedto takeadvantage of

advancesinnetworktechnologies to speedthe flowofdataoverthenetworks. Frame

relay services aredesignedtohandlespeeds of

1.5Mbps;

in

theory they

_maygomuch

higher. In concept,a_{frame relay}connectionis a virtual connectionbetweentwopoints

ratherthan a switched circuit connection. Itprovides a_{statistically}guaranteeddatarate,

and hasthe_capacityto routetrafficaround failures inthe net.This eliminatestheneed

(andexpense) ofthe_redundancythatis

typically

built intoaprivateline.

Overall,

frame

relayservicesoffersuperiorperformancewithreduced administrative and operational

costs compared with privatelines.

(6)

As thedemand forcolorand color

imagery

forpublication grows,andthe

necessityfortheirremote reproduction grows with

it,

the_capacityofthesenetworks must

alsoincrease. The developmentoffiberopticsis a responseto thisneed. Afiberoptic

network hasthreeelements: alightsource,an optical fiberand alight detector. The light

source _{may be}a_{light emitting diode}or

LED,

oralaser diode. This device convertsthe

outgoingelectrical signal intoan optical form. Ofthe two sourcesthelaser isthe most

powerfulat tenmilliwattscomparedto0.1 millwattsforthe LED. Thereceptor,or

photodiode, convertstheoptical signalback into an electrical one atthereceptionnode.

fiber,

corresponding loss

Thenext_type, gradedindex

fiber,

improvestheperformancecharacteristics

by focusing

theinternalreflectionstoward theaxis ofthe

fiber,

increasing

the_{bandwidth capacity}

overthemultimodefiber

by

afactoroften. The

best,

and most_{costly breed}offiber is

monomode. It has a corediameteroftenmicro-metersand a_{bandwidth capacity 100}to

1000timesthatof_multimode, on average around 100 GHz (100 billion Hertz ).

Monomoderequires alaser diodeasthelight source.

Fiber has severaladvantages over copper besides bandwidth. Signal

loss,

or

attenuation, is

lower,

so longer lengthsof cable canbe laidwithoutthesame numberof

repeaters or signal

boosting

stations as acomparable conventional net. Thereisno

vulnerabilityto_anyelectromagneticinterferenceor noisebecausethesignal isoptical, not

electronic, soerrorratesare minimal _{for analog}ordigitalsignals.Theraw materialis

silicon,farcheaper and more abundantthancopper, andtypical fibercableis strong as

wellaspliable, withthe sametensilestrength assteel.Thereis noelectromagnetic

radiation from

fiber,

so lines may berunin a

building

without_usinga conduit.Forthe

same_reason, fiber is extremely difficultto wiretap, addinga measureof_securityto

sensitivetransmissions. Onemajordisadvantageisthe

difficulty

of_storingcableinthe

field. Thefibersmustbeextruded as

they

areneeded, andshould notbe spooled,asthis

candamagethe

integrity

ofthe_{fiber bundle. Until recently splicing}was amajorproblem

inthefield aswell.Cables werearc_welded, glued withan_epoxyresinorjoinedwith a

mechanical connector. Allofthesemethodsdegradedthepowerlevel tosome

degree,

andthusretardedthedevelopment ofbranchnetworks_{using fiber. This limitation}to

point-to-pointusesisone reason

long

distancephone companies were _amongthe firstto

adopt

fiber,

whileits use

by

localcarriershas been hindered. New connector

technology

hasremovedthisobstacleandtheresultis the_{steady (if}slow) adoption offiberasthe

preferred cable medium.

While fiberopticsbids fairtodominatethe terrestrialdatanets, thecommu

nications satellite remainsaformidablerival. Satellitenetworks experienced are

naissancein the_early 1980's withthedevelopmentoflessexpensiveearthstationsto

transmit andreceive

data,

not_{only for}voice and commercial_{traffic, but}entertainment.

News

broadcasting

via satellite goesbackto

1962,

withthelaunchofthe firstsuccessful

been launchedtoservethe

broadcasting

industry,

_makingnews,sports and other

entertainment and educational_programming availableto _virtuallyanyspot on theplanet

with a_receivingantenna.Whilethe_qualityofthe_{programming is} asubjectfor

debate,

the_{revolutionary}nature ofthemediumisundeniable.Thisrevolution isevidentinthe

high speeddatatransmission_capability oftoday's satellite systems.

An orbitingsatelliteis_nothingmore orless thana communications transmission

device. Itreceives asignal fromaground _station,amplifiesthatsignal andbroadcasts it

toalltheearthstations capableof_{receiving its}transmissions. Satellite systemshavethree

segments. Thespace_segment,

including

the satelliteitselfandits subsystems; thesignal

segmentwiththeantenna andtransponderarraysto send and receive

data;

andtheground

segment,comprised oftheearth-_{basedstations thatlinkthesatellitewiththe terrestrial}

networks.

Thespace segmenthas a number of components: _{the satellite, the}system

thatplacedit inorbit andmaintainscontrol,andtheorbit itself. Communicationsatellites

areplacedin geosynchronous orbit. Atan altitudeof22,300miles (35,800

kilometers)

theorbital speedofthe satellite_exactlymatches therotational speed oftheearth around

its axis.To an observer onthegroundthesatellite maintainsthesamepositionoverhead

24hours aday. Asa resultit isavailable to_{any receiving}antennain its broadcast

"footprint",

or areaofcoverage. One

difficulty

theextremeorbital altitudeincurs isa

noticeable

delay

in signal reception of250milliseconds caused

by

the time ittakesforthe

signal to travelfromthe groundtothe satellite andback. Thiscanbea problemfor data

communications protocolsthatdonottakeaccount ofthe

delay

factor.

The satellites,or"birds"comeintwo_{basic types, based}onthemethod used for

stabilizing theminorbit. Spin stabilized models are cylindricalinshape and spin at 100

rpm. Theouter shellofthe cylinderiscoveredwith solar_cells, halfalways exposedto

sunlight. Theantenna_{is kept stationary}

by

anelectric despinmotor. Three axisbirds are

kept stable

by

aninternalgyro.Thesatellitedoesnotspin, sothesolar cellsaremounted

onarmsin large flatarraystocatchthesunlight.

Battery

backups are available onboth

typesofsatellitesforthosebriefperiodsin orbit whenthereisno directsun forthe solar

panels. The stabilizingsystems are a marvel of_engineering,capable of_maintaining

antenna alignment ofless than0.1. Acommand and control system onthe groundis in

constant contact

by

_{telemetry, monitoring}on-board systems and_makingattitude

adjustments withthebird'sthrusters asneeded. Ifall goes wellthesatellitewillhave a

thrustersandthepossible obsolescenceofits systems

by

technicaladvancementsonthe

ground.

Thesignal segment consists ofthebroadcasttransponders and antennathat

receive,process and retransmitthedatasent

by

the_originatingground station. Likea

fibernet,thesatellite's bandwidth ismeasured in Hertz

(Hz),

orcyclesper second.The

transmission

device,

called a_transponder, amplifiesthesignal received

by

thesatellite's

antenna,amplifiesitand converts and retransmitsthesignal through theantennato the

receivingearthstation.One transponder,with36MHzof

bandwidth,

canbroadcastat

frequencies from 4to 6GHz. Atypicalcommunication satellite carries 12to36

transpondersin their_array,with a potential

broadcasting

_capacityequaltoor greaterthan

anycommunications medium. The antennaisusedforreception andtransmissionofthe

datasignal.Three importantcharacteristics ofthe antenna subsystemare_gain, direction

and "footprint". Antennagainisthestrengthofthe signaltransmittedwhenit isprojected

in a singledirection. Highgaintransmissionshave highsignalstrength anda_narrowly

focused beam. Low gaintransmissionshavea_relativelyweaksignalstrength,butthe

transmissioncovers amuch widerareaoftheearth's surface. Thesize ofthese areas are

the "footprints"ofthesatellite. Television broadcastsatellites

typically

have

large,

low-gain

"footprints",

whiledatacommunications_{birds usually have}a_narrower, high-gain

focus. Somesatelliteshave both systems onboardtoincreasetheirflexibility. The

important distinction is the typeofinformation

being

broadcastandits intended audience.

Themost commonbands forsatellitetransmissionarethe C-Bandandthe

Ku-Band. C-Band hasan_uplink,or_reception,

frequency

of6GHz and a

downlink,

or

transmission,

frequency

of4GHz. The Ku-Band has anuplink

frequency

of 14GHz anda

downlink

frequency

of12GHz. The downlink

frequency

determinesthe characteristics of

thefinal transmission.

C-Band,

themostcommon

broadcasting

band,

has alow-gain

signalanda_verywidefootprint. Its signalis virtually immunetoatmospheric

disturbances,

andcan passthrough

heavy

weatherlikerain or

fog

withoutdisruption. This

lattercharacteristic, unfortunately, is alsotrue of groundbased C-Bandtransmitterslike

microwaverelays, andthesecanjamthelesspowerfulsatellite signals.The bestsolution

has been tolocate earthstationsforsatelliteC-Band inremoterural locationswhere

microwave radiationis less prevalent.This of course necessitatestheuse of some

terrestrial linkwith usersites, usuallycable. C-Bandearthstations also requirelarge and

expensive antennastoreceivetheweak signals. Ku-Bandtransmissionsareacomplement

interferencethatallows Ku-Bandantennastobe based intheheart of urban areas.Earth

stationfacilities are smaller andless expensivethanacomparable C-Bandstation.

Ku-Band isvulnerabletoweather

disturbances,

a serious problemif itoccurs

during

peak hours forsignaltraffic.

Togetthemost out ofthegenerousbandwidthof satellite systems aningenious formof_{multiplexing is}used similartothatemployedinterrestrial networks. Called Time Division Multiple

Access,

or

TDMA,

itallowsmultiple signals tobetransmitted

by

a single_{transponder, using} thefullchannelbandwidth. Topermit_{this, every}audioordata

signal mustbeconvertedto_sequentiallymodulatedpulses,spacedintimesono twousers

will ever_occupythesametimeframe fortransmission.TDMAearth stations are

equipped withmodemsthat transmitandreceivethepulsed signals.Themodemtransmits

data in high bit/s bursts.

Memory

circuits orbuffers storethe

incoming

burst

transmissions. Thisstoredinput isretransmittedasa continuous signal.Transmission

speeds of several millions ofbits/s are routine. A statistical errordetectioncalledForward Error Correction is usedtomaintaindata integrity. This statistical routine places extra encoding in thedata streamthat_{may be} extractedandchecked

by

thereceiver withoutthe

necessity forretransmission. Anerror rate of1 in 10million ispossible withthissystem.

The ground segment of satellitecommunicationshas beenrevolutionized

by

the

development ofsmall, lowercost earth stations.

This,

morethan_anyother

factor,

isthe

reason satellite networks remaincompetitive.This development is adirectresult ofthe

increase in satellite_capabilityoverthelast fifteenyears. Inthe_early

days,

satelliteswere small, primitiveaffairs withlimitedcapacity.Earth stationswererequiredto house much

ofthe transmissionand data processing capabilityofthesystem as wellasthe

large,

and veryexpensiveantennas. Modemsatellites arehuge

by

comparisonand_carrywithinthem

highly

sophisticatedtransmissionand receptionequipment. Themore capablethe

satellites

become,

theless _complex,and less_costly,theearthstation. An exampleis

antennasize. Anoldstation mightrequire adishover 100feet in

diameter,

_costing hundredsofthousandsofdollars.

Today,

a_{satisfactory receiving dish may be}as small as ayardacross andcostlessthan $2000. Asa matter of

design,

anearth station_may transmit,receive,orboth

depending

ontheintendedapplication.

There arefour basictypes. The

high-capacity

stationis used

by

major

telecommunications carriers, users

big

enoughto requirefeeder line accessdirectto the

station. It

typically

has alarge diameterreflector

dish,

and_connectingstructuresthat

supply. Astationinthis_{category has}thelookandprice

tag

of aNASAfacility. The

mid-capacitystationis most often used

by

private corporationsfortheirin-house networks.

Thesenets have varyingapplicationsdependenton theparticularneeds ofthecompany.

They

may handle videoconferencing , email , dataorvoicetrafficandthecost will

dependon thedesiredcapabilities. Ahigh-endsysteminthis_categorycould_easily

top

$1,000,000.Butifeach earth stationis connectedto theothersinthenetwork

they

canall

sharethesame satellite_capacitywith noadditional costsincurred. A lessexpensive

version ofthisbasicconceptistheVSAT_network,composed of oneMaster Earth

Station,

or

MES,

and perhapsthousandsofVSAT terminals_sharingthecapabilities ofthe

MES. Theeconomic _{advantage, again,}is theshared satellite capacity. The

last,

andleast

expensivedesign isthereceive_onlystation. These are_usuallyveryspecific intheir

application, and_{may be} configuredfor

data,

_video, voice ora combination of allthree.

Theadvantagesofsatellitenetworksincludestable costs. Theprice oftrans

mission over a singlelinkis independentofthedistance betweenthe _sendingand

receiving station. Sinceall satellite signals are

broadcast,

thecostofthe transmissionis

alsoindependentofthenumber of_receiving stations. High bandwidthallows satellitesto

handle largeamounts ofdatawith_{extremely low} error rates.

They

are alsoidealforusers

with_{geographically dispersed}

locations,

orundevelopedterrestrial networks. The

disadvantages includethesignal

delay

of250ms imposed

by

theextreme altitude

requiredforthe geosynchronousorbit.Thisis noticeableinvoicecommunicationsand

creates severe_efficiencyproblemswithdatatransmissionprotocolsthatarenot adapted

forthisdelay. Despitetheadvancesinrecent_years,earth stationsize and costremain

formidable obstaclesthatwillberelieved_onlywhenthehigh-powered satellitesofthe

nexttechnicalgeneration comeinto general use. Satellitesignalsare

line-of-sight,

and

few

building

codesguarantee against_anyobstructionthatwould renderthestation

useless. Andsinceall satellitesignals are

broadcast, they

are vulnerabletointerference

by

weatherorelectromagnetic transmissions.

Security

is anissue as_well, and_anysensitive

data will require encryption.

Having

surveyedtheterrestrialand space-based systemsusedfor analogand

digitaldataandvoice_{transmission,}a closer examination ofthenature of_analogand

digitalsignal propagation andtheirbehavior inthesesystemsis inorder.

Analog

transmission, designed primarily forvoicetraffic, dependsonthemodulationofthe

amplitudeand/or

frequency

ofthesignal. Foraconventionaltelephone call, spoken voice

electrical energy.Thevariations intonearetranslatedintocontinuous variationsin carrier

wave _strength,oramplitude. Wave

frequency,

orthenumber oftimesawaverepeats

during

an

interval,

_mayalsobemodulatedto_carrythesignal.

Analog

service_{is generally}availableto thecustomerinthree transmissiongrades:

narrowband,voice-band andwideband. Thethroughputrates forthe threetypes of serviceis dependent onthebandwidthandtheelectromagnetic propertiesofthecircuit

usedforthetransmission.As stated_earlier,the transmissionspeedof a networkisa

functionofthebandwidthofthecommunicationline. Thewiderthe

bandwidth,

the faster

the rate of transmission.

Narrowband facilities are created

by

_subdividing avoice-bandcircuitor

by

grouping severaltransmission

by

differentuserson a single circuit_using timesharing.

Transmission ratesfornarrowband arefrom 45 to300bps. Teletypesystemsthat

connecttomessage _{switching facilities}arethemost common example

ofnarrowband application.

Voice-bandfacilities haveabandwidthof

3000Hz,

ascomparedto narrow-band's

200to 400Hzrange. Datatransmissionspeedis differentiated

by

the typeof voice-band

systemutilized, eitherswitched

dial-up

transmissionorleased dedicated line. For

transmissionovertheswitchedlinesthedatarate is between 4800and

7200bps,

with

speeds_upto9600bps iftheswitches aremodem electronics. Speedoverthededicated

line mayrangefrom 9600to

19200bps,

iftheline is conditioned.Thisisone ofthe

key

differences between theswitched network andleased lines. Thecommunicationscarrier

cantune or

"condition"

aleasedline because itssignal _{routing is fixed. Traffic}on a

switchednetworkvaries _accordingto the traffic. Aleased linecanbeconditioned

by

the

carrier_{using fixed}equalizers tocorrect signaldistortions caused

by

attenuation.

Althoughlowdataspeeds_{may be}employedon bothnarrowband and voice-band circuits, it shouldbenotedthatlow-datathroughputrates onavoice circuitfallswell

belowthe maximumpotential rateforthat typeof_circuit, whilethenarrow-band

transmitting

atthesame rate_{is operating}neartheupperlimitsofitscapacity.

Facilities withahigher bandwidththanvoice circuits are called widebandor

group-bandsystemsbecause

they

permit abroader bandwidth

by

_groupinga numberof

voice-band circuits_{together, combining}theircapacities.Wideband facilitiesare available

onlyon leased linesand allowtransmissionrates greaterthan19200bps. Asnoted, the

transmission ratesforwideband networksdependson theservice offered

by

the_carriers,

Thetransmissionof_{data may be}eithersynchronous orasynchronous.

Asynchronous transmission_{is generally}referredtoas_start/stoptransmission.One

character at atimeistransmittedand received. Start and_{stop data bits} are addedto

separate characters and synchronizethereceiver withthe transmitter.This lessens the

likelihoodthatdatawill becomegarbled. Eachcharacterisencodedintoa seriesof

electricalpulses,

beginning

the transmissionwith a startpulse.Thecharacteritself

(the string of_pulses)is followed

by

a_stoppulse toindicatethat thecomplete character

has been transmitted.

Thestart_pulse,or

bit,

standsforatransitionfromacharacter marktoaspace.

When nodata is

being

transmitted thenetworkline is ina

holding

or_markingcondition.

The start_pulse, or

bit,

tells the_receivingnodethat thenextbit isthe

beginning

of a

character of_{data. The stop bit}places theline back into a_{markingposition,}

telling

the receiverthata complete characterhas been transmitted, and

indicating

that theline is

readytoacceptanew startbit.

Thetransmissionof an eightbitcharacter necessitates 10 or 11

bits,

depending

on thelengthofthe _{stop bit. The}eighthbit may beemployedas a_{parity bit for}error

correction and detection. Inthe_{start/stopmode, transmission}begins again foreach new

characterand stopsafter each characterissent.Becausesynchronizationbegins againfor

each_{character,any}

timing

errors are cleared attheendof eachcharacter.

Asynchronoustransmission_{is generally}used fortransmissionrates of9600bpsoverthe

switched networks and_up to 19200bpsover a shortdistance-directconnection leased

line.

Synchronous transmission_{involves sending}a set ofcharactersin a continuousbit

stream.Inthis modeoftransmission a

timing

signal or clockin a modem orotherdevice isusedat each endoftheconnectiontoestablishtherateofdatatransmissionandto

permitthedevicesconnectedto themodemto

identify

the characterswhile

they

are

being

transmittedorreceived.

Timing

_{may be}provided

by

the terminaldevice itselfor a

communication system componentlike a multiplexer. Regardlessofthe

timing

source

used,beforethedatatransmissioncan commencethe _sendingand_receivingcomponents

oftheconnection must establishsynchronizationbetweenthemselves. To maintainthe

synchronizationbetween the_sendingclock andthe_receivingclockforthelengthoftime

thatatransmissionis in progress, special characters called"syn" characters are

number ofbitsper_character,asthecodedinformationtobe transmitted. Thereceiver

recognizes and synchronizesitself usingthestream of syn characters.

Oncethe transmissionis synchronizedthemaintransmission_mayproceed.

Characters are groupedinto blocks ofcharactersthatrequireabufferor_memorystorage

area.Complex circuit paths are requiredforsynchronoustransmissionbecausethe

receiving devicemust remain insync withthe

transmitting

deviceforthedurationofthe

transmission. The datarates employed arein the2000bpsrange.

Theactualtransmissionofdata iseither serial or parallel.Forserialtransmission

thebitsof a particularcharacteraretransmittedin sequence on oneline. Parallel

transmissionsendsthecharacters_{serially but}thebitsthat comprise each characterare

sentinparallel. Acharacter_consistingof eightbits istransmittedover eightlines. Extra

linesmightbeneededforcontrolor_{parity bits. Parallel}transmissionis

frequently

used in

computer-to-peripheral connectionsbutnot onnetworks otherthanleased lines because

oftheextra expense oftheadditional circuits.Becausethe totalcharacter_{may be}

transmittedat onetime_usingparallel

lines,

fasteroveralldatatransmission speed rates

canbeachievedovercomparableserial paths.

The_{first step}tochange a continuous_analogsignal todigitalistoconvertittoa

series of numbers. This is achieved

by

_sampling the timefunctionofthe transmission.

Theresultantlist ofnumbers represent a continuous seriesofvaluesthathave beencoded

intoasetofdiscretecodes. Formostdigitaltransmissions the formchosen forthe code

wordis a

binary

_number,either 1 or0.

Analog

todigital conversionis called_quantizing .

Thepurposeis tochangethecontinuous _analogsignalto adiscrete digitalsignal

by

coding.Inuniformquantization, the continuous valuesaredivided intouniformregions

orlevelsof signal strength and anintegercode isassigned toeach region.This integer

valueisnot a_precise,one-to-one _{correspondence,}butarounded offnumberthat_closely

Therearethreegeneraltypesof quantizers:

1.

Counting

quantizers these _sequentiallycountthrougheach_{quantizing level.}

2. Serialquantizers generate acode wordbit

by

bit,

beginning

withthemost

significantbitthrough to theleastsignificantbit.

3. Parallel quantizers generateallbitsof acompletecodeword at

thesametime.

Toconvertthe digitalsignalbackto_analoga

digital-to-analog

converter orDAC

isused. Sincethedigital signalis formed

by

_{assigning discrete}numerical valuesto the

continuous_analogsignal

levels,

thereverse operationisperformed

by

_assigningthe

analogvaluetoits digitalnumerical value or code. Againthis isnot a seamless recreation

ofthe_analogsignal,butan_extremelyclose approximation. This fact isonereasondie

hard audiophileshave fought hardto

keep

_analogmusic_recording alive theultimate

sound _qualityof an_{analog recording is simply}richerthanacompactdisc becauseallthe

intermediatetones are present without_anytruncation. Digitalrecordings,onthe other

hand,

can be almosttooclean.

There are problems with_{analog transmission,}

however,

andtheseproblems are

directly

relatedtotheelectrical properties ofcoppertwistedpaircable.There arefour

primaryareasthatcan _{negatively impact}the signal:_{attenuation, capacitance,}crosstalk

and

delay

distortion.

Attenuation As anelectrical signal istransmitted throughacable, it losesstrength

becauseoftheresistanceofthecableto theflow of electrons.This flaw iscalled

attenuation and refersto thereductioninthe amplitude ofthesignal. Invoice

communications, attenuationreducesthevolume ofphoneorradio conversation. Telcos

compensateforattenuation

by installing

amplifiers or"boosters"at selectedlocationsto

increase signalstrength.Asecond cause ofattenuationiscreated

by

theuse of electrical

filterstoformthe telephonechannel passband.Phone companiesuse highandlowpass

filterstopassthrough_onlya small portion ofthe20000Hz bandwidthof soundthat the

thefactthathigherfrequencies attenuatefasterthanlower

frequencies,

theidealpassband

ofthechannel _{may become}skewed ordistorted.

Becauseoftheuse oflow andhighpass

filters,

a greatdealof attenuation _may

occurbelow 300Hzand above 3300Hz. The higher incidenceofattenuation atthehigher

frequenciescreates anon-linearresponse from 300Hzto

3300Hz,

withthegreatest

degradationatthehigherendofthe

frequency

spectrum.

Theeffect of attenuation on adigitalsignalis similartoitseffecton an _analog

signal inthatitcanreducetheheightofthe square wavesthatcomprisethe signal. Instead ofthe amplifiersusedin analog transmission, digital lines employ dataregenerators or "repeaters"

tocompensateforthe lossof signalstrength. Therepeaterreceives adigital pulse andregeneratesitatits original specifiedheight and_{width,removing}thedistortion.

Though bothamplifiersand repeaters are meanttocounteracttheeffects of signal

attenuation,thesignalsproduced

by

eachsystem are _{very different in kind. Amplifiers}

use_analogsignals andboost not_onlythesignal

itself,

_{but any}noise ordistortion as well.

Repeaters operate withdigitalsignals and remove_{any distortion} ofthedatasincethe the

pulse orbit isrestoredto itsoriginal specification

by

the repeater. Thisis the_primary

reasonthat _{data quality is}superiorfor digital transmission,and one of_{the reasons, along} withincreased

bandwidth,

thatlong-distancecarriers are_{using digital lines.}

Capacitance The capacitance of an electrical cableis _{its ability}to storean electrical

charge andtoresistrapid changesin thestrength ofthatcharge. Capacitance ina cable is

dependenton thedielectric constant ofthecable whichrefers to thethicknessofthe

insulating

materialthatsurroundsthecable.

Capacitancehappens betweentwowires of apair andbetweenadjacentpairsin thesamecable. Forawire pairthecapacitanceis calledmutualcapacitance. Theeffect of mutual capacitancein voicetransmissionshiftsthephase ofthe _analogsignal. Inmost

casesthisis not_{objectionable,} since voice communications are continuous, and frequencies vary onlyoverthe narrowbandthatis usedforspoken conversation. But

when adigital signalisemployed theeffect ofthis typeof capacitance canbetrouble. The

reasonforthisinvolvesthedistortion ofthe shape ofthedigitalpulse.Ifthemutual capacitanceis to great,itcombinesitseffects with _{attenuation,causing data}

Crosstalk Ifa signal fromone cable appears on anothercrosstalk_{may be}present.

Whiletheeffectis usually_negligible,mosttwistedpairlines exhibitcrosstalkto some

degree,

since a signal on an "excited"or active pair alwaysinduces a signal on aninactive

or

"quiet"

line. Thetrouble ariseswhenthe signal ontheactiveline has sufficentstrength

tointerferewiththetrafficon its neighboringpairs. Crosstalk isproportionalto the

dielctricconstantofa given cable. The higherthedielectric constant ofacablethehigher

thecapacitance ofthatcable.

Therefore,

capacitanceis also proportionalto thelevel of

crosstalk.

Delay

distortion In a channelfreeof

distortion,

allfrequenciespassthroughatthe

samerate.Thiscreates a constantlinear relationship between the

frequency

andthephase

inrelationtotime. Distortion occurs whenthe_{relationship between}the

frequency

andthe

phasebecomesnon-linear.Signalpropagation throughatransmission medium can occur

atdiferentspeedsbecauseofthe effectsof passbandfilters and signalharmonics for

complextransmissions. Low andhigh frequenciestakelongerto travelthrougha

transmissionmediumthan middlefrequencies.

Whilethissignal

delay

has a minimal effectonvoice_{transmission,}theeffect on digital

datatransmissioncanbe severe, sincethelatearrival ofa givenpulseforone character

may bemistakenasthe arrival ofthefirstpulse ofthe next character.

Mostofthesepoints _applytosomedegreeto_{both analog}anddigitalsystems, but

whatdesignrequirements are specific todigital systems alone?

Analog

systemshave been

designedover_many

decades,

and withtheir

flaws,

have servedthe telecommunications

industry

well.But digitalnetsare ofmore recent_pedigree,andtheirdesignconsiderations

areless well understood. The

following

setof requirements arebasic toan_{understanding}

ofthedesignrequirements:

1. Requiredbittransmissionrate

2. Maximumallowablebiterror rate

3. Maximumsystembandwidth

5. Constructioncost

6. Powerutilization ofthesignaldetector

7. Acquisitiontime ofthe detector

Required bittransmissionrate Therequiredbittransmissionrate is afunctionofthe

information tobetransmittedandthelevelofworkneededpriorto transmission.This is

dependenton theapplication ofthesystem orhow itwillbeused.Ifa client needsto

transmitcriticaldatatoits management

division, they

shouldknow howmuch datawill

typically

be sentandhowtimesensitivethe_{information may be. The}required bit

transmissionrate shouldbeminimized asmuchaspossiblebeforethecommunication

designis begun. Therearealwaystrade-offs toconsider. Hardwarecosts,production

costs,realestateand electrical power requirements mustbeweighed. Special purpose

softwarefor datacompression _{may be}necessary.

Maximumbiterror rate Thenature ofthe_{data's sensitivity}will determinethe

maximumtolerablebiterror rate. Datais much more vulnerabletoerrorsthanvoiceor

video.Forthelatterthereare established signal

-to-noise ratiosforacceptable

transmissionandreception. For

data,

the maximumbiterror rate is determined

by

the

source.Forexample, financial datarequires a smallerbiterror rate thanentertainment

data. National defensedatawould need eventighter tolerances.If_necessary, forward

error correction canbe built intothe systemtomaximize data integrity.

Maximumsystembandwidth This isoftendetermined

by

thechannel usedto transmit

thesignal. _{Two primary factors}areconsidered: the transmissioncharacteristics ofthe

cable,

i.e.,

coaxial orfiberor_{twisted pair,}andthe_regulatoryenvironment ofthe operation. The Federal Communications Commission

(FCC)

assignsbandwidth for

terrestrial transmissions.

Maximumtransmittedsignal power This affectsthesignal-to-noise ratio andthebit

errorrateofthereceivedtransmission. Theminimumbiterrorrate fora given signal

transmissionpower output_{may be}controlled_usingvariousphaseor

frequency

shift

thephase angletoachievetheoptimumbiterror ratefroma giventransmitterpower

level. Noise reductionis often possible as amethodtoimprovethe signal-to-noiseratio

ifthereis sufficent control overthe transmissionpath.Additiveor extraneous noisecan

beminimized

by

_shieldingthelines.

Construction costs Systemsthatperform well are moreexpensivethan systemsthat

perform poorly. Thereisno

"cheap"

waytodesignandconstructaneffectivedigital

transmissionsystem. Thegoodnewsisthatsome hardwarecosts are _coming

down,

and

thereare_manygood off

-the-shelfcomponents available. Theenvironmentforthe

equipment mustbe considered. Itwouldbe a_{false economy}tofail toprovide adequateair

conditioningor ventilation.

Powerutilizationofthe signaldetector Themorecomplexthesignaldetector

is,

the

morepower requiredto operateit. Phase-lockloopsrequire morejuicethanpassive filters. Quadrature detectorsperform more complex operationsthan

binary

detectors. The

locationof some

detectors,

_{especially for datacollection,may be in}remote areas,or_rely

on solar power. Acareful andconcise analysis ofthepowerbudget may be requiredto

balancethepowerneeds ofthedetectorwithotherfactors

likeoptimumbiterror rate.

Acquisitiontimeofthedetector Detectors need time toacquirethe

incoming

signal.

Thisacquisitiontime _maynotbeseriousfortransmissionsthat are not_{time sensitive,}

since a_quantityofbitsatthe

beginning

ofa messagecangivethedetectortime toadjust

itself. Transmissionsthatare short orthatrequirethe transferof_{data shortly}afterthe

transmissionbegins necessitatesthata considerable amount of efforttakeplace toprovide

acoherentdetectionofthesignal. This is done

by

theuse ofcoherentdetectorthatderives

acarrier signal fromanexternalsourcelockedto the_transmitter,or_employincoherent

detectors. The latterarea compromise since

they

requireahighersignal

-to-noise ratioto

deliverthe samelevelofperformance as acoherentdetector.

They

areless_expensive,

however,

and_mayrepresent a viablealternativeifthe signal strength can_{be readily}

To employthesedatapaths,filesrequirecareful preparationforefficient

transmission. Pagefilesareprepared onapplication software and_generally saved asa

Postscript file. Postscript isa pagedescription languagethatis device

independent,

allowingcross-platform compatibility._{In theory, any}Postscript- compatibleRIPor

imagesettercan _successfullyplotthe fileand maketheseparations. Document

illustrationsare_{usually included}withtheregularfileas anEncapsulated Postscriptor

EPS_{file. The EPS file may}contain_anycombination oftext, imagesorgraphics andpage

elements canbetransmittedindependentoftheirresolution.

(7)

Other file formats areused for file imageencapsulation. Tagged Image Format

File,

or

TIFF,

isa platform independentpicturefile andthemost_commonlyused format.

Anotheris

GIF,

for Graphics Interchange

Format,

and

JPEG,

theJoint Photographic

Expert's

Group

format forscreendisplayedimages. TIFFandEPS files often add

complex designandimageelementstoa

file,

and thiscanbe a source of problems.Some

clientsdesignpagesthat_maycontain25 or moreTIFFandEPS files.

Anentiredocument withfiles likethiscould_{occupy 50MB} ormore ofstoragespace.

Transmissionof afilethis sizeovera conventional 14.4Kbpsmodemcouldtake

severalhours.

(8)

One strategytoovercomethisproblemis filecompression. Software for file

compression reduces transmission time

by

_{removing unnecessary bits}ofinformation from

the file. Afterthefile isreceived, thebitsarerestored andthedataprocessedinto

separationsfor proofingand platemaking. Differentcompressionratios will reducefile

sizein fixedproportions-

4:1, 8:1, 10:1,

_{and soon.The ratio chosen}

may dependon the

sizeoffiletobe transmittedandthespeed requiredfortransmission. Filecompression

routines make high-speedtransmissionpossible

by

_reducingthephysical sizeofthefile

without_{compromising its}content.

(9)

_{The validity}ofthis lastpointis_conditional,

howeveronthe compressionratio andthe type ofcompressionused. Setthecompression

ratiotoo

high,

andthere willbe degradationof quality.Thetwogeneral categories of

compression software arecalledLOSSYandLOSSLESS. LOSSYsoftware causessome

data loss inthecompressed

file,

_usuallyanimagethatwill_{qnly be displayed}on a

computer screen or other context wheretheperceived lossof_{quality is}negligible.

LOSSLESS compressionisused for dataapplicationsthatrequirezerodata loss. For

Oncethefile isprepared,formattedand compressedit is ready fortransmission.

Filetransferprotocols, or

FTP,

facilitatethis

by

_settingproceduresfor datatransmission.

Protocols allowthe transmissionof_{data between anytwo computers,}regardlessoftype.

Asender logs onto the_receivingsystem'sremote serverwithauseridand_password,

and uses a menu or a seriesofcommandlinepromptstosendor receivedata files. Ifthe

system _allows,theusercan

log

onas aguest anonymously.This isreferredtoas

"anonymous ftp". (Inpractice,most systemsrequireguests to

log

on with an email

address or otheridentifierso systemusecanbe_tracked.) Once

they

have loggedonto the

systemtheuser_mayuploadtheirfilesto theremote server,wherethe servicebureaucan

p. 14-15

2.

Capron, H.L.,

Perron,

John

D.,

Computers & Information

Systems,

Third

Edition, Benjamin/Cummings,

Redwood

City, CA,

1993 p. 59-60

3. "Communications

Networking

Services",

February

1994,

Datapro Information Services Group: Communications

Series,

Delran NJ:

McGraw-Hill,

1994p. 7 - 9

4.

Boisseau,

M. ,High-SpeedNetworks , John

Wiley

and

Sons,

Chichester,

1994p. 1 14- 116

5.Boisseau,

M. , High-SpeedNetworks ,

John

Wiley

and

Sons, Chichester,

1994p. 135 - 136

6. "Communications

Networking

Services",

February

1994,

Datapro Information Services Group: Communications

Series,

Delran NJ:

McGraw-Hill,

1994p. 9

7.

Handler,

Christian"

Postscript Problems inPractice"

Newspaper

Techniques,

June

1994,

p.18- 20

8.

McDowell,

DavidQ. , "

Electronic Data Transfer"

The Prepress

Bulletin,

July/August

1994,

24-26

9.

Usenet/comp.compression/news.answers/compression-faq

/part 1 & 2

lO.Usenet/comp.compression/news.answers/

compressionfaq/part3

11. "Anonymous FTP:

Frequently

Asked Questions"

(on-line),March,1995,

available:http://www.cis.ohiostate.edu/hypertext/faq/usenet/

The developmentofdigitalworkflowsin printingand_{publishing has}createdtheneedfor

fast,

efficienttransmissionof graphic arts datafilesover networks. Signal attenuation

andtrafficonthe network,filetransfer protocols, datacompression,cross-platform

incompatibility,

andPostscripterrorsin clientfilescan anddocause significant_problems,

butto whatdegree? Basedon

industry

_experience,whatfactor hasthe greatestnegative

impactonthe_efficiencyof on-linefiletransfer?

Using

the _{surveymethod, this study}

will examinethisquestion, collectdataon these

factors,

analyze theresults and establish

abaselineofinformation for future inquiry.

Hypothesis

Question: There is apreferencefor Postscripterrors asthe most criticalfactor

affectingon-linefiletransferefficiency.

H: Thereisa preferencefora_category

Ho: Thereis NOpreferencefora_category

H 1: There isapreferencefor Postscripterrors asthe

most criticalfactor affecting on-linefiletransferefficiency.

Limitations:

Resultsarebasedonthedataprovided

by

therespondents.

Any

conclusions reached are

valid_{only for}the sample,and no generalconclusions are expressedorimplied for any

other population.

Delimitations:

The study includes onlythemembersofthepopulation sample as described in Chapter 5.

Noother entities ofthe_printingand_publishing

industry

were surveyed.

Methodology

Using

the 1995 Buyer's Resource

Directory

ofServicesand Suppliers intheDecember28

issue of

Publishing

& Production Executivemagazineas a_{population, the}entire

population of 132 servicebureausand_catalogprinters thatsupport electronic filetransfer

was selectedforthesurvey. Themembers ofthe sample receivedacoverletter

accompanyingthe_{survey soliciting}theirparticipation.Therewere 32responsesreceived

over a period offourmonths.Completedsurveysprovidedthe dataandcommentsfrom

therespondentsbasedontheirexperienceforthecalendar year 1994. The _{final survey}

data wastabulated, analyzed andthe_summaryandconclusions setforth inthe

body

ofthe _thesis.(l)

Thestatisticaltestforthis _{study is Chi-square. The data}evaluatedisorganized

intocategories,and this test_{is specifically designed}to testhypothesesabout_category

data,

inthis case,factors affecting the_efficiencyof network workflow. Amultinomial

study isthemodel.

Alphalevel= .05

The nullhypothesis is:

Ho: Ofsix

key

factors,

thereisno preferencefor any category

having

thegreatest

negative impacton on-line workflow efficiency.

The surveyconsists of26 questionsthat

identify

thelevelof experienceofthebureau

with electronicfiletransfer

technology

andmanagement and queriesthemon the

following

categories:

SURVEY CATEGORIES

Category

I

1)

PROBLEM AREAS: Whatfactors of electronicfiletransfercreatethegreatest

obstaclesto the_efficiencyofnetwork workflow ?

1. Transmission 2. FiletransferProtocols 3. File formats

4. Filesize 5.Postscripterrors

6. Cross-platform

incompatibility

Category

II

2)

INTERNETCONNECTION METHODS

-allthat_apply

3)

DESKTOP APPLICATIONS SUPPORTED

4)

FILEFORMATS SUPPORTED

5)

MARKET/GEOGRAPHICALAREA: Whatmarketis served

6)

FILE SERVERS/STORAGE

7)

COMPUTERS

8)

DATACOMPRESSION

9)

EXPERIENCE

Datacollected from

Category

Iquestions was usedfor hypothesis testing.

Questions in

Category

1 1elicitedbasicinformationabouttherelatedhardwareand software employed

by

therespondents inthissegment ofthe

industry,

theirexperience withthe_technologyandto solicitopinionsfromtherespondents onthe current andfuture

use ofnetworks asfile

delivery

pathsbased ontheiractual experiencewiththe

technologyin 1994. Foracompletebreakdownofthe

Category

II dataseeAppendixA.

ELECTRONIC FILE TRANSMISSION SURVEY

1

)

Whattype_ofmarketdoyou_primarilyserve?

Commercial

( )

Catalog

( )

Specialty

(

)

Color

( )

Other_

2)

Whatpercentage_ofyourwork consists_ofcustomerfiles received overthe

Internetor other off-site network connection? %

3)

Whatconnection methodisused?

(

check all that_apply

)

14.4kmodem

( )

28.8kmodem

(

)

Switched56

(

)

ISDN

(

)

Tl

( )

4)

What

desktop

applications are supported?

(

check allthat_apply

)

Quark

(

)

Pagemaker

(

)

Freehand

( )

Photoshop ( )

Illustrator

(

)

Acrobat

( )

Trapping/Imposition

(

)

Other

5)

File formatssupported

(

Checkallthat_apply

)

TIFF

( )

GIF

( )

EPS

( )

JPEG

( )

SCHEX LWCT

( )

Other

6)

What

desktop

platform(s)doyou useforpage production _oftransmittedfiles ?

Macintosh

()

IBMPCor clone

( )

OS/2

( )

PowerPC

(

)

UNIX Workstation

( )

Other

7)

GEOGRAPHICALAREA: Whatmarketisserved? Northeast

( )

Southeast

( )

Midwest

( )

8)

Datacompressionformatssupported

(

Checkall that_apply

)

Stuffit()

CompressPro

( )

LZW

( )

MacCompress

( )

JPEG

( )

Other

9)

How manyyearshasyourbusinessaccepted customer pagefilesvia modem or

othertransmissionmethod?

*Lessthan 1 yr.

( )

1-2yr.

( )

3-5yr.

( )

Over 5 yr.

( )

* _If

you answeredlessthan 1 year go question#20

10)

How manycustomerfileswere transmitted

during

1994?

<20

()

20-50

()

51-150()

151-₃₅₀

()

350- ₅₀₀

()

501-750

()

751- ₁₀₀₀

()

Morethan 1000

( )

-(State#

)

11)

During

1994,

how_manyworkhours werelost becausea

client'

sfile failedto

transmit_properlydue tolineconditions, noise or modem problems?

Lessthanl0()

10-₂₀

( )

21-30()

31-50()

50- 100

( )

More than 100

()

- (State #

)

12)

During

1994,

how_manyworkhours werelost dueto

protocolerrors?

Less than 10

()

10-₂₀

( )

21-30()

31-50()

50

-100

( )

Morethan 100

()

- (State#

)

13)

In

1994,

how_manyworkhourswere lostduetoexcessivefilesize?

Less than 10

()

10-₂₀

( )

21-30()

31 _-50()

14)

During

1994,

how manyworkhours werelostduetodatacompression

errorsintransmittedfiles ?

Lessthan 10

()

10-₂₀

( )

21-30()

31-50()

50 - 100

(

)

Morethan 100

()

- (State #

)

15)

During

1994,

how manyworkhours werelostduetoPostScripterrors in

transmittedfiles ?

Lessthan 10

()

10-20()

21-30Q

31 -50()

50 - 100

( )

Morethan 100

()

- (State #

)

16)

For transmittedfiles ONLY-How_manyofthe

following

Postscripterrors occurred

during

1994?

Missing

fonts _{Too many fonts}

Clipping

paths Complexgraphics

TIFF& EPS _{files missing}

Missing

graphics components Other

(specify)

17)

Wherein theproductionprocess weretheseerrors first detected? File server

( )

RIP

(

)

Preflighting

(

)

Other

18)

In

1994,

how_manyworkhours were lost becausea customer used an incompatible software application tocreatethe transmittedfile ?

<10()

10-20()

21-30()

31-50()

50- 100

( )

Morethan 100

()

- (State #

)

19)

During

1994,

how _manyworkhours werededicatedto the _tracking,

indexing

and storage _oftransmittedfiles ?

<10()

10-20Q

21-30()

31-50()

50-100O

100-250

()

251-500

()

More than500- (State #

Answerthe

following

questions_usingthisscale:

1_-StronglyAgree 2-Somewhat Agree 3-Neutral

4-Somewhat Disagree

5-Strongly

Disagree

20)

Ourclients prefertosendtheir_{files electronically}via modemratherthanondisk.

12 3 4 5

21)

Electronic file

delivery

is more efficientthandisk.

12 3 4 5

22)

Postscripterrorintransmittedfiles isthemost critical technicalproblem.

12 3 4 5

23)

Storage and

indexing

isthemost critical filemanagement problem.

12 3 4 5

24)

Theuse of electronic file

delivery

willdouble inthe

next5years.

12 3 4 5

25)

Theneed forstandards at all levelsofdigitalproductionis critical.

12 3 4 5

26)

Fonts supported:

Truetype

(

)

Adobe Type 1

( )

Adobe Type 3

( )

Other

27)

Commentsand suggestions

1.

Blessing,

Rose "A NewandImproved 1995 Buyer'sResource"

Publishing

&

Production

Executive,

Dec.

28,

1994 p. 8 52

Froma_surveypopulationof132 servicebureaustherewere32responses.

3 1 ofthe32respondents answeredthe

Category

Iquestions usedfor hypothesistesting.

The datausedfor hypothesis

testing

wasderived fromthe

tally

ofthe

Category

I

questionsthatpolledforpreferences.

PREFERENCE DATA TOTALS

SCALE ****H**** ****Q****

MODEM PREF STRONG AGREE 3 SMWHT AGREE 6 MORE EFFICNT 7 8

PS CRITICAL 2 3

STOR/INDEX 6 11