AddingVoicetoanOfficeComputerNetworkD.C.Swinehart,L.C.Stewart,andS.M.OrnsteinCSL-83-8August1983[P83-00009]Abstract:ThispaperdescribesthearchitectureandinitialimplementationofanexperimentaltelephonesystemdevelopedbytheComputerScienceLaboratoryattheXeroxPaloAltoResearchCenter(PARCCSL).Aspeciallydesignedprocessor(Etherphone)connectstoatelephoneinstrumentandtransmitsdigitizedvoice,signalling,andsupervisoryinformationindiscretepacketsovertheEthernetlocalareanetwork.Whenusedbyitself,anEtherphoneprovidesthefunctionsofaconventionaltelephone,butitcomesintoitsownwhencombinedwiththecapabilitiesofanearbyofficeworkstation,avoicefileservice,andothersharedservicessuchasdatabases.Mostoftheworksofarhasgoneintothebasicprovisionsforvoiceswitchingandtransmission.Todaythesystemsupportsordinarytelephonecallsandsimplevoicemessageservices.Wewillexpandthesefunctionsasweexploretheintegrationofvoicewithourexperimentalofficesystems.AversionofthispaperwillappearintheproceedingsoftheIEEEGlobeCom'83Conference,November,1983.CRCategoriesandSubjectDescriptors:C.2.4,H.4.3,H.1.2,C.2.2AdditionalKeywordsandPhrases:Voice,recordedvoice,telephones,Ethernet,Cedar,distributedsystemsXEROXXeroxCorporationPaloAltoResearchCenter3333CoyoteHillRoadPaloAlto,California94304pî ìï^kî÷îî�î#¨î,wî:$qî ìïXèî 2îw î@îQî–î"‚î&î(1î*¬rî ìïSeî ïSeîî†ïSe sî ìïH^tî#ïH^îôïH^îSî‹îCî!Í î*î,ÿî0ê î;Vî=î?6 î ìïF*îÐîÎîôîúî!…î(iî. î5–î7Oî9Ùî>îAnî ìïCöîƒîUîîîŠî%œî+üî2ë î;ÖîB@îDî ìïAÁîÐ î-îî!†î'lî+º î2Àî5­ î=� îEgî ìï?�î�îîdîîî àî$rî'Îî-Öî2î5¡î7¨î;“î=¯ î ìï=Xîéîsîèî¬î÷ î$µ î+üî.‘î/Üî4£î7‘î9Œî<¼î@²î ìï;$î î› î[îîiîRî#i î+¹î-î0îî3Wî8Ðî;½î?žî ìï8ïî±îOîJ î½î [î"î$©î(Hî*Nî,‹î/Xî3î6î8�îî Ûînî?îîÓîÙ î*' î2î4¢î8èî:®î>nî@å îGÖî ìïP î›îÚîáîD î&mî,‹î.’î4eî7t î?òîBîGàî ìïMÕ îÛîƒîî"—î&î+äî0½î3»î6kî:$ îBWîEkî ìïK¡îîÜ îî5îíî Œî&á î ®ïIeî‰î&î-îÄî/ î œî#à î+î-Mî2±î4Jî8 î?˜îBßîCéî ìïG1 î~îtîêîÕî"k î*î/î1¢î7† î?‡ îFtî ìïDüî 7îÊ îî¸îî¾î$-î*Èî-kî3jî6#î;µî=dîBë î ìïBÈ î¢îv îrîkîÉî#Qî%î'¨î+#î,�î.ëî4mî:îî>î?ÊîB(îFIî ìï@“ î† îšîbî!Õ î).î,�î.Zî1Cî2\î7òî:™ îAîCéî ìï>_ îºîîƒ î Çî%¹î(Xî-‚î/# î6Tî;PîAlîD î ìï<* î‡î+î0îû î(Wî+Hî.� î6+î7þî;Áî=ŸîAcîEîGàî ìï9öî ”îLî$î8îjî!úî#¼î)(î,bî.î0Œî5Ÿ î;éî? îFØî ìï7Áî î¯î ®ï5† îîYî¯îjîýî!n î'ëî-4î.C î7A î>�îA,îB; î ìï3QîD î6î®î[î gî%¿î,�î3w î<{î?à îG/î ìï1î”îCîà î‘îƒî"„î&P î-Ýî/� î6î7¾î:ûî>eîD±î ìï.èî tîÞ îiîiî›î!ìî$V î+ìî-¥î0³ î75îAî@ÕîEBîG/î ìï+¯î,îLî"îºîHî! î# î)Õî,´î0eî6 î<®î?`îD:îG/î ìï){ î1î îîî¬î!‚î&?î(î*¢î.J î5©î;¦î>0 îFHî ìï'FîÊ îïîüî«î î,j |î ìï#jî )î{î ®ï�î4îÊîîî1îÙî Ãî$qî&¨î(’î.•î1“î6î:%î<~î?�îAEîEÛî ìïYîôîÖî®îjîõî îî'"î+î/ª î7aî:î>QîDYîGÀî ìï%î uî¾îîàî9î î$yî&î)fî/ƒî1Zî6üî:¸î<šî@MîFtî ìïðîhî¨îÇî$î!˜ î(à î13î4½î8žî<íî?òîC’î ìï¼î ­ îÄîÙîÆ î øî%pî)êî.òî1Nî5,î9 îBîCËîDòî ìï‡ î îiîþîî´îãî"Qî&<î'þî*gî.àî1üî5î7\î:3î<,î?àîD îFIî ìïSî °îÓî/î?î î€î ®ï î$îdîÆ îKî"Rî&6î'çî)Ûî,Sî.î0qî4Iî6Íî9Ôî>1î?âîAÖîG“î ìï é î³îóî—î™î î$Fî&î(» î/Åî4Ýî6¤î:fî<ÞîCMîGàî ìï µî QîuîöîÀî/îÕî € î'üî)œî+íî/âî1Œî6& î<²î?/îC’xîÕï î#Pî'î,Xî1íÿ {TVm$4AddingVoicetoanOfficeComputerNetworkassistancetothosecallingfromoutsidetheEtherphonesystem.2.3VoiceasdataLeavingarecordedmessagecanbeaneffectivesubstituteforthosecallsthatgounanswered.Telephoneansweringmachinesmakethispossible,buttheirimperativenaturedemandsawell-constructed,composedmessageratherthananinformalcommunication.Fewofusareabletoproducesuchacompositioninrealtime.Thesemachinesalienatecallers,whooftenhangupwithoutleavinganyusefulmessage.Ourapproachtothisproblemistoshifttheresponsibilityforproducingavoicemessagetothecaller.Thesystemcanallowthesendertorecord,audition,andmodifyamessagebeforesendingit--ordecidingnotto.Themessagemightcontaintext,recordedvoice,oracombination.Ifexperiencewithelectronictextmessagesisanyguide,userswillcometopreferrecordedmessagestotelephonecallsinsomesituations.Somerecentstand-alonevoicemessagesystemssupporttheseideas[Maxemchuk].Voiceinmessagesanddocumentswillfindapplicationfarbeyondsimpletelephony.Weintendtoexplorevoiceannotationofordinaryofficedocuments,spokenreminders,musicalprompts,andothercombinations.Insummary,wefeelthatourcomputingandcommunicationsenvironmentcanbebroughttobearonvoiceintwoways.Onewayistoimproveourcontroloverotherwiseordinaryvoicecommunications;theotheristoincorporatethevoicemediumintoourintegratedenvironmentonanequalfootingwithtext,graphics,anddata.Whilethefacilitieswehavebuiltorproposedarenotentirelynew,webelievethatthefullintegrationofvoiceintoourcomputer-basedofficesystemswillmakeexistingfunctionsmoreeffectiveandnewapplicationspossible.XEROXPARC,CSL-83-8,AUGUST,1983wî ìïg/xî…ïg/î"|î%–î&ïî(|î+Ôî1{î ìï_/ î!îÏînîÓî:î"î$c î+ä|î ìï[Eî )î îÎ{î ®ïW[î1îžîœî6î"î$7î&jî,1 î2«î5*î9 î<^î?oîA¡ î ìïU&î�îÚî·î ?î"µî(#î*xî-“ î47î8[î>î>þî ìïRòî¤î;î‰îðî !î%ú î0Eî3”î5Žî7�î:1î=kî?ZîDóîHeî ìïP½ î©îRîî}îzî#~î(�î-î0î3ªî7 î9î>"îBÚîEvî ìïN‰î ®ïLJî´îÖî¨îmî î!¤î#vî&´î)7 î1Ìî4-î:ßî<,î?ãîE]îG/î ìïJîîïîzîîÍî<î"°î$nî)%î.ûî1Âî6�î7Èî=/îA�îF²îHî ìïGáî Éîsîxî+ïGá{îmïGáîUïGáî_îÐî"àî'Ùî+î0×î4Üî6ºî7ý î@úîB• î ìïE¬î û î/îÛîªî îŸî#¶î'(î)Çî-eî/î3î8Ãî>“î@5îF€î ìïCxî šî- î¤îyî� î$ñî(„î-Üî2Ûî7çî;pî>î î ®ïA8î–îLî/îîî!çî$šî'� î.©î0Øî5Êî:6 î@÷îC‰îGàî ìï?îñîŸ î•îiî!î% î,iî16 î8 î=;îCîEðî ìï<Ð î ®ï8Qî�îÛîî¶î‰îî%÷î(³ î2î î;î=‘î?†îDÂîFtî ìï6î çînîî±îYîQîî}î î%‚î(î,¨î/¶î5Ôî;Wî>Þî ìï3èî Rîøîjî înîÔî nî%ãî(Áî+S î1Ñ î9æî;óî=êîA°îFtî ìï1´î îÒî�îôîî{ î$åî'î*bî-±î/|î5‚î7Ýî:Yî?`îB®îDÝî ìï/î àîeî î+î îÂî!¿î$p î.–î2‘î7¶î:‡î>aîC‘î ìï-Kî îî»î© î ?xîÕï î#Pî'î,Xî1íÿTVm$wAddingVoicetoanOfficeComputerNetwork53.SystemArchitecture3.1PARCEnvironmentFormostofficeapplications,adistributednetworkofpersonalworkstations,interconnectedbyhigh-bandwidthlocal-areanetworksorbyspecializedPABXlines,issupplantingthetraditionalcentralcomputinginstallation.AtPARC,boththestandardEthernet,operatingat10.0Mbps,andanearlierprototypeEthernet,operatingat3.0Mbps,areingeneraluse[Metcalfe,Crane].Thesenetworkslinkpersonalworkstationstoeachotherandtosharedresourcessuchasfileservers,mailservers,andhigh-qualitylaserprinters[Birrell82,Mitchell].Communicationsoutsidethelocalareaareprovidedprimarilybyleasedlines--mostoperatingat9.6or56Kbps,withsomeoperatingatupto1.5Mbps[Boggs,NS].Severaltypesofpersonalworkstationsareinuse,includingtheXerox1100,1108,and1132(Dorado)processors[Thacker,Lampson].Thesesameprocessorsareusedasthecontrollersformostservers.Everyworkstationhasahigh-resolutionbitmapdisplay(1000by800pixels),akeyboard,andamouse[Smith].Inourlaboratory,mostusersworkwithintheCedarprogrammingenvironment.Cedarisanexperimentalintegratedsystemthatisusedforsoftwaredevelopmentandcomputer-aideddesign,aswellasforday-to-dayoperationofofficeapplications,suchasdocumentpreparation,graphics,andelectronicmail[Brotz,Smith].OurapproachtoapplicationsresearchistobuildprototypeapplicationsbasedontheCedarenvironment,thentousetheminourdailywork.Thisapproachencouragesustocarrythedevelopmentofourimplementationsfarenoughthatperformanceandreliabilityproblemsdonotimpairourabilitytoevaluatetheirusefulness.Oncetheyareintroduced,theseapplicationssupplybothideasandusefulcomponentsforfurtherdevelopments.Mostofourapplicationsarestructuredsothatuserscaneitheroperatethemdirectly,orwriteprogramsthatcombinetheirfunctionswiththoseofotherfacilities.3.2BasicArchitecturaldecisionsThegoalsofimprovedtelephonefunctionalityandintegratedvoiceaddtwonewrequirementstotheexistingcapabilitiesinCedar:rapidandversatilecontrolovervoicetransmissionandswitching,andahighperformancevoicestoragecapability.Wesurveyedseveralpossiblearchitecturesforthesystem.SubscriberlineaccesstoavoicestoragesystemanduseofourexistingCentrexservicethroughDTMFsignallingwasrejectedduetothelowbandwidthandtheinflexiblecontroloverswitching.UseofacommercialPABXwasattractive,butthenecessaryswitchingcapabilitieswerenotcommerciallyavailable.TheuseofourowncomputerstocontroltheswitchingoperationsofastandardPABXwasrejectedprimarilyduetothenontechnicaldifficultiesofarrangingthenecessarycooperativeeffort.Althoughreluctanttoundertakethenecessarydevelopmentwork,weconcludedthatthemosteffectivewaytosatisfyourneedswastoconstructourowntransmissionandswitchingsystem.WeelectedtousetheEthernettotransmitvoiceaswellascontrolinformation.WechoseEthernetbecauseofitsXEROXPARC,CSL-83-8,AUGUST,1983xî¿ïg/î!¶î$Ðî&(î'µî+ î0KwîHDïg/zî ìï^õî Èî… |î ìï[î )îy {î ®ïW=îœî;îS î…î ñ î(&î-Àî/¼î5ƒ î> îG“î ìïU îñ î3î î!ðî#ù î*íî/Jî2ëî4e î;éî>V îEî ìïRÔîå îaî{îVî"±î%/î*èî1î7Bî8ùî<î@gîC=îEKî ìïPŸîQîsî¶îrî Óî%<î'³î)…î.}î1 î7¦î<œî@ÂîFÂî ìïNk}î´ïNkî²ïNk îæîØîMî!1î$,{î&ïNkî&£ïNkî*Èî1 î4€î6rî9î>MîAªîFØî ìïL6 îçîeî½ î!` }î'×ïL6î(ÔïL6 î2³î7Àî:bî=ëîA'îC½î ìïJîýî îDî“îî�î$Áî&nî(¿î*—î,�î0³î3âî7‰î=¼î?iîA�îCRîE¢î ìïGÍî¬{îÌïGÍî“ïGÍî˜î$îÕî!Q î)7î+ƒî-)î/îî5ûî8Rîî?AîE¨îHeî ìïA0îFî ®ï>ûîÍî© îéî–î dî$2î(Çî+wî/à î8à îAzîEâîGžî ìï<Ç î î�îíî¬î! î$6î&eî+Ï î3ðî6™ î@jîEîF¡î ìï:’î �î  î’î±î_î * î(î+4î,×î3: î:æî@¢îCO î ìï8^î îuî ®ï6)îçî=îB î /î%éî'¬î)±î-§î4> î<+î@dîBÀîEwî ìï3õ îGîaîîlîéî‹î! î$eî(.î+<î1. î84î9÷î;™î? îA^ î ìï1Àî ¯îDî°îâîÖî"® î*¼î-} î3°î9Ãî;Óî>RîBÁîEVî ìï/Œî £îî] î×î}î"–î$ñ î,Cî/Õ î7sî;íî?1îB·îEvî ìï-W î¥îïî¤ î"Nî%ãî'©î*A î1äî4D î:Õî<¥î?€îC îE¢î ìï+#îÖî_î­îqîîî#î%Ðî+jî.±î4¯î7Êî;iî="î@Á xîE ï+#|î ìï'Gî )îé î9{î ®ï#jî�î1îîMî!» î)×î,¦ î35î6àî9¯îQî@ îA>îDÝî ìï˜î€îPîÝî¯îRîuî"Åî'cî,´î1• î7Öî:šî?ßîB¯îDvîFîî ìïdîËî†îè îÿî µî#Ò î*@î-î.Íî/ú î7[î;­î>\ îD«îG/î ìï/îãîÚ îÛî î"h î*½ î0²î3nî5Æî7cî9Ñî<¸îCJîDÜî ìïûî Pîj îîÚî î!©î%üî(­î-ßî3áî6�î8Pî:µ îBÊ î ìïÆî ¥îÎî-îA î!”î ®ï’îîîÿî!¹î$Zî*° î3#î7:î9¤î@€îC‘îF2î ìï ]îXîî­îÃî5îþî ‘î"'î'øî*jî-V î5 î7¾î=ºîBtîDæî ìï )î ®î6î¨îbî#îšî!@î#î&î'Äî,‰ î4~î7î:úî@³îEèîG´xîÕï î#Pî'î,Xî1íÿ ²TVm$!6AddingVoicetoanOfficeComputerNetworkpervasivenessinourenvironmentandinordertodemonstratetheeffectivenessofEthernetforvoice.ThepotentialoftheEthernetforpacketvoicetransmissionhasbeendescribedelsewhere[Shoch].Inthefollowingsection,wepresentonlyaveryconservativeanalysis.XEROXPARC,CSL-83-8,AUGUST,1983wî ìïg/xî…ïg/î"|î%–î&ïî(|î+Ôî1{î ìï_/ îiîî¢ î°î!hî#î&Êî(y î0Fî2¦ î:Ÿîþ îGÖî ìïXäîã îîÈî$Óî'2î*°î0®î4mî8 î>¹|î ìïUî ){î ®ïQ,îªî§î(îùî…î!”î#$î%¨ î,Ô î5î6æî<°î@~îBà î ìïN÷îbîéî|îâ î ôî$‘î(ßî+Šî-› î4  îWî@ùîDÆî ìïJŽî á îºîAîíîYî"Qî&¿î+œî/î1Ø î9äî=ïî?ÞîDÒî ìïHZ îåîüînî ®ïF%îoî‹îÙî^î$îvî"î$yî' î// î7sî;î=¹ îEŽî ìïCñ î;î×îˆîœî îî#¹î(Sî)þî+î/hî3Öî5¹ î<êî@#îBuîDèî ìïA¼î :îp î;îìîn î"9î#}î'î(žî*Öî/Òî1dî3œî9Qî>*îA î ìï?ˆî gîaî(î—îî î%~î)¼î,Wî01î3¨î90î=nî@5 î ìï=Sî ®ï;î~ î‹î×î%† î-µî2fî6ìî:î? îBŸîE�î ìï8êî îþîýî!î°î")î%w î, î3 î8òî<³îAÛîE@î ìï6µî «îQî î�îéîçî î$Ýî*âî.]î0¡î33 î9mî< îEaî ìï4�î W î¸î}îŸîeîÛî!’î%S î-nî1êî4` î:äî?*îCîGáî ìï2Lî rîðî± îî#—î&×î*eî/kî4¨î7 î:7 îB@îFíî ìï0îôîÖîÌî®î[îÙ î$œ î+—î-êî2¾î4`î5~î8î='î?Y îEûî ìï-äî î†î·î‚îÿîîî"&î&eî)…î- î2Áî4Îî:‘î>AîBÚîD¥î ìï+¯î ùîXî©îbîî®î ®ï)zîlîÛî¿îQî!î$A î,nî/ î6¾î:Cî;Íî?«îAk î ìï'Fî •îùî%îîÃî‹î!aî#.î(ò î0òî2|î5î6Wî;úî@\îBÚîF>î ìï%î*î‰î–îµ î Wî$î&©î*àî-<î1iî3!î7¦î<¤îA­ î ìï"Ý|î ìïî ){î ®ï$îßîî§îŽî"bî&# î.2î/Ìî1Ôî7ZîAî?˜ î ìïðîRîî5î=î"œî$ î)Zî,lî.Øuî1§ïðî2+ïðî6I{î;|ïðî<�ïðî?‚îDšî ìï» îäî˜î‚î”î"—î$´î(¶î.öî4 î<ÄîAÚîF·î ìï‡îPî[î² î&_î)xî-î1÷ î8° î?HîC4î ®ïRîîšî+îî"Ùî(ƒî*¥ î4µî9î<ÙîAéîFùî ìïî|î² îîÿ î&Öî(šî- î2Ðî4tî7 î? îE�î ìï éî vî…î›îaî‰î!äî&iî+÷î.î1Åî3¨î:î< î?fîEûî ìï µ î/î·îãî9î$àî&Rî*Nî-ƒî/„î2¹ î9wî;ü îBæîG/xîÕï î#Pî'î,Xî1íÿ "TVm$Ë8AddingVoicetoanOfficeComputerNetworkbandwidthavailableinanetworkdedicatedtovoicetransmissionis5Mbps,yielding28full-duplex"trunks"(55one-wayvoicestreams.)IfweestimateaTASIadvantageof1.6forthissizetrunkgroup[ATT],adedicated10MbpsEthernetcansupportabout45conversations.Ifatmost20%oftelephonesareinuseatonce,suchanetworkcouldsupportinexcessof225subscribers.Thisargumentrequiresthatcontroltrafficandothernon-voicetrafficisnegligiblecomparedtovoicetraffic.Thusitseemsclearthatasimplesingle-cableEthernetvoice-transmissionsystemcansupportasizeableinstallation.ThenumberofsubscriberscouldbefurtherincreasedbylinkinganumberofEthernetcableswithpacketgatewaysorconventionalcircuitswitches.Installationofamultiple-cablesystemwouldrequireattentiontousagepatternsandothertraffic-engineeringconsiderations.4.3SecuritySecuritycanbeaproblemwithEthernetoranyotherbroadcastmedium,sincenophysicalprotectionagainsteavesdroppingispossible.WeimposesecurityonourtransmissionsbyencryptingallvoiceandcontroltrafficusingtheDataEncryptionStandard[DES].Theavailabilityofsingle-chipDESdevicesoperatingat900Kbpsmakesthispossible.Wehandlethedistributionofkeysusingamethodsimilartothetrusted-authentication-serverapproachadvocatedbyNeedhamandSchroeder[Needham].4.4NewFunctionsThebroadcastnatureoftheEthernetadmitssomenewcommunicationpossibilities.ConferencecallsamongseveralEtherphonescanbeachievedwithouttheneedforspecialconference-bridgehardware:multicasttechniquespermitvoicepacketsfromagivenEtherphonetobereceivedandcombinedbyeachoftheothers[Forgie].Intheextreme,voicefromameetingorconferencecanbetransmittedonceandreceivedbyanynumberoflisteners,withoutconsuminganymorebandwidththanasingleconversationconsumes.4.5EtherphoneVoiceProtocolsThevoiceprotocolsfortheEtherphonearebasedontheprecedinganalysis.Wetransmit80008-bitsamplespersecond,usingtheindustry-standardmu-255encoding[Henning].TheEtherphoneactuallysupportstworelatedprotocols,oneforinteractivevoice(telephonecalls),theothertoplayandrecordstoredvoice.Theinteractive-voiceprotocolwasdesignedtomeetadelaybudgetof40millisecondsend-to-end.Thisdelayconsistsofapacketizationdelayof20milliseconds,hardwarelatencyof5millisecondsforencryptionandEthernettransmission,softwaredelaysofupto5milliseconds,andwhatwecallananti-jitterdelayof10milliseconds.Tomeetthisbudget,theprotocolspecifiesthetransmissionoffiftypacketspersecond,eachcontaining160voicesamplesand36bytesofaddressingandcontroloverhead.Anti-jitterdelayisintroducedbybufferingatthereceivingstationtoallowforvariationsinthearrivaltimesofpackets.Onemightsaytheprotocoloperateswithaboutone-halfpacketofbuffering.Thisdelaybudgetdoesnotallowtimeforretransmissionsintheeventoflostpackets.ThishasprovenXEROXPARC,CSL-83-8,AUGUST,1983wî ìïg/xî…ïg/î"|î%–î&ïî(|î+Ôî1{î ìï_/îôîÚî´î î�î%ïî'Éî+ˆ î3–î5.î6Žî:ÿî@lîB} î ìï\ûîšîî‚îî!yî#î%3î*Ÿî+Òî/™î6î7Ûî: î î@ùîB´ î ìïX’î SîîžîJîýîBîîëî#Êî(êî*¬î.ãî0¯î3Y î:Öî>îDBî ìïV]î ºîmîzî2îÑî"&î&4î'Ÿ î-éî4Kî5ùî9�î ®ïT)î_îèîî¢î¤îî"™ î*Aî0î;¹î@gîC&îHeî ìïQôî: îxî~îÙî!À î)î,ùî/î3ïî:%î±î?ìîE î ìï=î šî úî‡î%…î+ýî-ùî4Hî6ÿî=‚ |î ìï9&î )îN{î ®ï5Jîrî‰îÅîjî¶î#Hî'¥î+%î-ÿ î7ž î?@ îF€î ìï3îŠî3 îPîóîüî%Åî*éî-aî0Öî3,î7¿îC î ìï0áî· î�îßî`î#-î&‚î'šî+< î2ªî4Fî6$î;€î>%îDtîF^î ìï.­î ©î î5î»î�îòî!‘î%)î(”î)Âî/î0Ð î7Åî:Uîî?k îGRî ìïR îúîäî¾ î"+î'×î,8î.%î0jî2Kî3³ î< î>öîB†îDàîGžuî ìï {îïîÆïî·î~îq î£î!Øî%Mî'ýî-î/nî4êî:qî<ß îDÏîF–î ìïéîÇî8îîK î î"’î&"î+Iî-üî/Þî3nî5# î;ãî>–îCEî ®ï´ î@îî£ î»î!Ýî( î)Ìî,Rî2Uî6ìî8Áî<‘î>õ îE[îG/î ìï €îPîîÞî+îEî Rî"Æî%;î*¿î0Cî3tî7kî<ïîA`îC/ î ìï Lî î¿îdîœîîÊî!÷î$;î-Óî/‰î1ðî5­î7mî: î?IîBkîDçxîÕï î#Pî'î,Xî1í �TVm$ AddingVoicetoanOfficeComputerNetwork9acceptable,becausethenativepacketlossrateofwell-designedEthernetcomponentshasbeenshowntobelessthanonepacketintwomillion[Hupp].Recordingandplaybackofstoredvoicehasslightlydifferentcharacteristics.Transmissiondelayisnotparticularlyimportant,providedthatthestartupdelayfromrequesttoplaybackisreasonablyshort.Thestored-voiceprotocolcallsfor100millisecondsofbuffering.Theadditionalbufferingisdesirablebecausethesharedvoicefileservermaynotbeabletoschedulethetransmissiontimesofpacketsasaccuratelyasadedicatedvoiceterminal.Theadditionalbufferingalsopermitsretransmission,althoughwehavenotfoundtheneedtoimplementit.XEROXPARC,CSL-83-8,AUGUST,1983xî¿ïg/î!¶î$Ðî&(î'µî+ î0KwîHDïg/{î ìï_/ îïî îgî{î Ñî#xî&6î'ê î0„î6& î=Íî@>îC–îGàî ìï\ûî Ýîrî˜îDîŸîMîùî!¶î ®ïZ±înî7îîÛî"î%¶î(=î-î2Ðî;ú îDgîH#î ìïX|î c î® îiî =î# î%nî* î-¹î1"î5øî7¨î=qî>Þ îE¹î ìïVHî Þ î¤î-îVî­î"] î*Cî, î2‘î5ƒ î<îB8îC½î ìïTî)î£î$îÒîVî ~î#œî&,î(8î+Lî-î2×î5Q î=NîAîBæîGáî ìïQß îoî'î[îœî:î#î%ø î,zî2�î5dî:dîCÓî ìïOªî îZîÏîÜî<î™îGî$,xîÕï î#Pî'î,Xî1íÿ¢TVm$ 10AddingVoicetoanOfficeComputerNetwork5.MajorSystemComponents5.1HardwarechoicesPerhapsthemostsignificantaspectoftheEtherphonesystemarchitecturaldesignwasthechoiceofvoiceterminalequipment.GiventheexistingPARCenvironment,voiceterminalsweretheonlynewequipmentrequired.Thealternativesweexploredweretoaddspecialhardwareandsoftwaretoeachworkstation,ortodesignastandardizedEthernettelephoneperipheral--theEtherphone--thatwoulddoallofthenecessaryvoiceconversionandtransmission.WechosetheEtherphoneapproachforseveralreasons.Wewantedtomakevoicecapabilitiesavailabletousersoverourfullrangeofworkstations.Furthermore,wedidnotwanttoredesignthevoicehardwareforeachtypeofworkstation,norwereweconfidentthatallofthemcouldhandlethetransmissionandcontroloftelephoneconversationswithsufficientreliabilityandwithoutsubstantiallossofperformanceintheirotherduties.Anadditionalhardware-relateddecisionwasmotivatedbyeconomics.WewereabletolimitthesizeandspeedoftheEtherphone,andthusitscost,byrestrictingitsactivitiestothosethatcouldnotbereadilyperformedbywritingsoftwarefortheexistingworkstationsorservers.EtherphoneusersconversewitheachotherusingonlyEthernetcommunications.Tomakecallsoutsidethesystem,however,accesstothepublictelephonenetworkisneeded.Thepreferredmethod,transplantedfromtheconventionalPABXenvironment,wouldinvolveconnectingagroupofcentral-officetrunklinestoaserverthatwouldcompletetheconnectionsovertheEthernet.Forourprototypesystem,wechoseinsteadtoprovideeachEtherphonewithajackforconnectiontoanexistingsubscriberline.Tocompletetelephonecallsinvolvingnon-Etherphoneusers,theEtherphoneconnectsthetelephoneinstrumenttothesubscriberline.ThischoiceallowstherelativelysmallcommunityofEtherphoneuserstoretaintheirshortextensionnumbers,avoidsthecostofdevelopingatrunkserver,andpermitsdirectuseofthesubscriberlineasabackupifthehardwareorsoftwarefails.5.2SystemOrganizationInadditiontotheEtherphones,wehavedesignedandimplementedatelephonecontrolserverandavoicefileserver,bothofwhichareCedar-basedapplicationsprograms.Figure1showsthestructureoftheresultingEtherphonesystem.TheEtherphoneisresponsibleforvoicedigitization,fortheanaloginterfacetotheswitchedtelephonenetwork,andforimplementingthevoice-transmissionprotocols.Itisdesignedtobeavoiceperipheral,withoutlocalintelligenceorsystemcontrolresponsibility.Instead,itreportsuseractionstothetelephonecontrolserver,whichreturnsdetailedcommandsthatcontrolitsfunctions.Thetelephonecontrolserveristhesystemcontroller.ItsresponsibilitiesareanalogoustothecontrolresponsibilitiesofaconventionalPABX:monitoringthestateofthesystem,keepingtrackofthestateofeachEtherphone,andsettingupallconnections.Itmustalsocoordinatetheoperationofthesoftwareinusers'workstations.Thisworkstationsoftwareprovidesimproveduserinterfacesforthetelephoneandothermoreexperimentalapplications.XEROXPARC,CSL-83-8,AUGUST,1983wî ìïg/xîèïg/î"ßî%ùî'Rî(ßî,7î1uzî ìï^õî ÈîØî• |î ìï[î )î~{î ®ïW=îãî@îš î0î"Rî$î&f î-äî2] î:@î>ŒîA6îC“îGÖî ìïUî  î: }î™ïUîÃïUîèî!hî&”î+ {î3¡ïUî4QïUî7U}îüîD’îF^î ìïPŸ î½î�îNî­îæ î"úî(°î/ î5½î7Duî9³ïPŸî:¦ïPŸ{î@üïPŸîAvïPŸ}îBƒïPŸîBòïPŸîEaî ìïNkî ãî Ãîmî¼îÀîD î"î$À î,ëî/eî3!{î5qïNkî6XïNkî<âîBÐîDþî ìïL7îÚîîbî+îùî § î'Þî-³î/|î3î6Hî8íî;’î?wîAJ î ìïJ îcî…îôîcî¹îbî#Õî&.î)»î/¾î1õî5 î8*î9Ý îA˜îDîGgî ìïGÎî.îî0î î¶î¤î#Mî%Ï î-Óî0¬î5�î7\î=Õ îFtî ìïE™ îê îîËî× î$§î'Rî) î1î2½î6î9£î ®ïCeîó î]îßî%)î'Çî.&î0 î7 î9‰î<Ìî?¸îAYîD’îFäî ìïA0î ÂîÂîšî îîåî# î%î(Fî*` î0ëî2ä î8©î:vî>3îA îE îGžî ìï>üî}îAî=îïî!hî#¥î&î+ î2ýî4Áî ®ï<Ç îbîîíî!<î$¡î(tî,Rî/Ÿî5zî@<îB—îF€î ìï:’îÇî8îî î )î!éî$Zî(¦î/î4xî5õî;'î>îD+î ìï8^ î›îÙî îÿî## î+aî/eî4 î:Õî;Õî?®îA= î ìï6*î  îÏîqî�î�îQîsî$Oî&£ î.î1$î3xî9iî<î>‡îD»î ìï3õî "îüî¾î{î•îÕ î&dî)�î*Æî-¸î0 î7î8Ìî:Ë}î?äï3õî@hï3õ{îF�ï3õîFäï3õî ìï1Áî >îRîÔîî"A î,¯î0°î3; î:çî@®îC8î ìï/Œ îÕî|}îÔï/ŒîYï/Œ{î[ï/Œî¾ï/Œîaî!tî%±î)×î,/ î2î5°î<çî>˜ îFî ìï-Xî ›îˆîÐîOîoî"xî&½î)î+ìî-¦ î4­î5Øî9™î=ÿ}î@·ï-XîA~ï-XîE­î ìï+#î aîîy îî¾îlî–î!kî"Ëî%+î+4î,÷î2p|î ìï'Gî )îñ {î ®ï#kî‰îî¾î* î “î"Æî&î+àî.¤ î7uî87ï#kî8§ï#kî>HîBê{îFØï#kîG}ï#kî ìï!7uî ï!7î ¬ï!7îuîÄ{î"ï!7îúï!7î1îæîïî > î(( î/¹î6î:‹î;»î?ÃîBîGÖî ìïî Kîñ îqî ®ïÍî_ îºîÿ î î!"î$� î+éî.î09î4wî9÷î;î=¸îC8î ìï™î î\îž îbîÆî+5}î0¤ï™{î1„ï™î2ï™î3î4pî:0î;ãî=Øî?îBž î ìïdîèî îXî îyî$î,Öî1óî3:î7Òî:¼î?Iî@èîC8î ìï0îŸîîîÄî üî'áî*¯î/bî1< î ®ïûuî„ïûîôïûî†î{îúïûî]ïûîdî!Âî&; î,Ðî.Êî8î:iî@ÒîBîDÜî ìïÇîMîîT î€î#Z î*‡î,ùî0<î2î4yî9^î>œîB!îCìîF^î ìï’î ›î î�î>î™î¡î!‡ î)Uî*Âî. î0â î7�î9òî@îAÁîDî ìï ^î ŽuîXï ^î@ï ^ {î§ï ^îwï ^î… î!ãî'Pî,Óî2üî5é î<î>9î@�îFØî ìï *î ‹î îY xîÕï î#Pî'î,Xî1í TVm$¤AddingVoicetoanOfficeComputerNetwork11Thevoicefileserverusesageneral-purposecomputerwithattacheddiskstorageforvoice.Itperformsstandardfileserverfunctions,butisspecializedforthereal-timeneedsoftelephony.Finally,existingstandardfileserversanddata-baseservicesareusedforstorageoftelephonedirectoryinformationandforstorageofusers'callfiltersandotherinformation.Thefollowingsectionsamplifythedescriptionsofthesemajorsystemcomponents.5.3EtherphoneTheEtherphoneisadual-processorcomputerwithinterfacesfortheEthernet,DESencryption,RS-232serialdevices,andvoice.Themainprocessorisresponsiblefornetworkcommunicationsandcontrolwhiletheslaveprocessorhandlesvoicesignal-processingfunctions.Ananalogboard,adigitalboard,andapowersupplyoccupyaconvection-cooledcabinetmeasuring12"x13"x5".Thispackageisdesignedtositunderauser'sdesk,whilethetelephoneset,microphone,andspeakeroccupypositionsofconvenience.ThisarrangementisshowninFigure2.Figure3isablockdiagramoftheEtherphone'sinternalarchitecture.Theanalogboardiscenteredaroundan8by8analogcrossbarswitchthatinterconnectsvariousvoicesourcesandsinks:telephoneset,telephoneline,analog-to-digitalconverters,DTMFdecoder,microphoneandspeaker,andlinelevelauxiliaryinputsandoutputs.Theanalog-to-digitalconversionfunctionsareaccomplishedbycoder-decoder(CODEC)devices.Thetelephonesetandtelephonelineinterfacesareconnectedbyrelayssothatapowerfailureorsystemcrashwillrestorestandardtelephoneservice.Thedigitalboardcontainsthetwoprocessors,memorysystems,timinglogic,anddigitalinterfacesfortheEthernet,RS-232devices,DESencryption,analog-to-digitalconversion,andcontroloftheanaloghardware.Awatchdogtimerisprovidedforautomaticrecoveryfromanintermittentfault.ThemainprocessorisanIntel8088with8KbytesofEPROMand56KofRAM.DESencryptionisaccomplishedbya900Kbpssinglechipdevicewithdirectmemoryaccess(DMA).TheEthernetcontrollerisaninternalXeroxLSIpartusingtheprotocolsofthe3MbpsexperimentalEthernet,butoperatingat1.5Mbps.TheRS-232interfacepermitsthetheconnectionofalocaldisplayandkeyboardasanoption.ProgramswrittenintheClanguagesupplyallofitsfunctionsexceptforasmallnumberoflow-leveldevicedrivers,whicharewritteninanassemblylanguage.Thesoftwareincludesaround-robin-scheduledmultitaskoperatingsystem,andanetworkpackagethatimplementsboththevoiceprotocolsandprotocolsforconnectingalocalcontrolprogramtothetelephonecontrolserver.Thislocalcontrolprogramcommunicatesuseractions(suchasliftingtheswitchhookorkeyingina"5"onthetelephone)totheserverwithoutinterpretation.CommandsfromthecontrolserverinstructtheEtherphone'slocalcontrolprogramtoestablishEthernetvoiceconnections,configurethecrossbarswitch,generateprogrammedtonesequences,andmanagethetelephonelineinterface.Theslaveprocessorisalsoan8088.Ithasaccessto8KofprivateEPROM,2KofRAM,andsharedaccessto48Kofmainmemory.Theslaveprocessorexecutesasmall,carefullycoded,assembly-languageprogram.Itsfunctionsincludesilencedetection,thecombinationofincomingpacketstoachieveXEROXPARC,CSL-83-8,AUGUST,1983xî\ïg/î!Sî$mî%Åî'Rî*ªî/èwîG~ïg/{î ®ï_,uîjï_,îï_,î·îï{îµï_,î|ï_,î“î¡î&�î,Ÿî/žî4ýî7ÐîˆîBWîC³î ìï\øî‡îðîý îSîÔî @ î'%î)cî+Âî1“î5tî7- î ®ïZÃî“îyîïî4î"¡î%3î+#î0 î28î5Pî7iî;÷î=‹îC½î ìïX� îvî-îkîîÖî ¬î#7î'î)Ïî-n î ®ïVZî†î˜î¹îÄî"# î)¹î+rî.üî2òî7m |î ìïR~î ) {î ®ïN£î¶ îfîî\ î#¯î* î-U î3¯î6î8¬î>ÚîB\ î ìïLnîðî´îûîØîèuî!æïLnî"üïLn{î%xïLnî&?ïLnî+±î-C î4šî6ýî<{ îFØî ìïJ:î½î�uîïJ:î’ïJ:{î~ïJ:îEïJ:î¯î#Ùî'‹î27 î8«î;î? îDîEVî ìïHî=îöî"îRîÄîzî ¥î+çî0³î7Wî9îî;%î=¼î>òîA1îDMî ìïEÑî Nîÿî£îtîlîŒîXî Öî$�î&Öî-"î/� î7|î:*î?îCÉî ìïCœî ž î»îÎ îÀî $î$lî&î*|î,î0jî1—î2üî4î7×î=(î>ÚîA2 î ìïAhî î ®ï?3î£î$î9îÂîoî$Jî&Wî'©î)Áî+î/•î5 î9aîóîCÿî ìï:Ë î¬î‚îùîÏî¥î# î(Íî-î/ñî5^î8UîBª î ìï8–îîl î î î&/î,Óî2 î4úî;hî=œî@jîFØî ìï6b îîZîÕîÉî¬î hî#.î$Pî(vî,Èî.„î2÷î6„î9'î=¥îC8î ìï4-î ®ï1ùî‘îÖîÙîHî³î"k î)fî.ßî4Bî8¨î<]î? îCe î ìï/Äî îhîUî$î4î!u î(˜î2¾ î9êî<‘îA3îBÛîE*î ìï-�îLîÙîî­îî"ëî%(î+î1 î4tî6e î=ñî ®ï+[î‚îûî îrî_î¢î"ãî%úî(Lî+Üî-‘î3=î5ðî8òî:§î?fîB´ î ìï)'î † î>îhîÁî…îjî"„î%Ãî*6î-€î1�î7,î;hî@âîCéî ìï&ò î@îÀîÄîîî%îñî"éî&§î)î/!î0ïî3bî4«î8¬ î@ûîGî ìï$¾îîœîÔîîéîÄî%fî*Wî,³î/ î6î7¼î8âî<$î@ÓîC†î ìï"Šî šî Šî ®ï Uî¸îWîñî=î¬î"^î&»î(˜î*=î,î1ïî6+î8Uî9kî<õîBîC´î ìï!îîéîßîîµîKî!#î&çî,íî/¬î5 î:Yî;jî ìïìîÉîÇîyîîî#Pî(qî+ î2gî5ƒî7Áî;4îAîCœî ìï¸î l î î î•î‹î#\î%Mî'ðî.‰î3~î8%î;‚î? îDî ìïƒ îöîî±înî .î$Nî&À î.î/Ûî4]î6î7Zî:î<î>Œ îEoîG/î ìïOî ûî îî#Lî&µî)î-Ìî1Ûî6Óî95 îA”îDÜî ìïî¡îvî7îî ¾ î(½î/î1ˆî7î;¿îAj î ìïæî  îËîƒî˜îøî$Nî' î ®ï²îxîÒîØî6îõîØî"gî#Ñî&9î*9î+Úî.!î/Íî4\î:Vî<žî>IîBîE)î ìï }î íî�î‰î6î§î`î ,î#‡î)�î.üî0î4î9žî=øî ìï Iî4î‘îòî3î# î)½î, î4Ïî6êî=SîB•îD¥xîÕï î#Pî'î,Xî1íÿ TVm$€12AddingVoicetoanOfficeComputerNetworkconference-callbridging,echosuppression,gaincontrol,CODECcontrol,andlow-levelbuffermanagementinsharedmemory.TheoverallperformanceoftheEtherphoneissufficienttosupporttwosimultaneousEthernetconversations.Forexample,twoconversationsareneededinordertoforwardanarrivingoutsidecalltoanattendant'sEtherphonewhenthetelephonesetisalreadybeingusedforanEthernetcall.Inadifferentconfiguration,theEtherphonewillsupportafour-partyconferencecall.BecauseeachEtherphonehasitsowncrystal-controlledclock,synchronizationoftwoEtherphonesparticipatinginaconversationpresentsanintriguingproblem.ApairofEtherphonesmayhaveclocksdifferingbyasmuchasonepartin10,000.Inthesteadystate,thisfrequencyerrorcausesthequantityofbufferedvoiceatthereceivingEtherphonetoslowlyincreaseordecrease.Sincesilencedetectionisusedtoreducetransmissionbandwidth,thecorrectbufferdepthisreestablishedduringeachsilentinterval.Communicationswiththevoicefileserveravoidthisproblembyuseofsoftwarefeedback--thefileserverisdrivenbytheEtherphoneclock.5.4TelephoneControlServerThetelephonecontrolserverperformsthefunctionsnormallyassociatedwiththecommoncontrolfacilitiesinaconventionalPABXortelephoneswitchingoffice.However,becauseitdoesnothavetoswitchortransmitanyoftheactualvoicetraffic,ithasnospecialhardwareneedsandrequiresonlymodestcomputingpowertosupportitsactivities.Thetelephonecontrolserversuppliestwoclassesoffunctions:Etherphoneintelligenceandcallprocessing.ThecontrolservercontainstheEtherphoneintelligencesoftwarethatinterpretsuseractionsatanEtherphone.MostEtherphoneshaveonlythestandardDTMFkeypad,butasmalldisplayandkeyboardcanbeaddedtoprovideamoreeffectiveuserinterfacewhenaworkstationisnotavailable.Ineithercase,controlserversoftwareinterpretsandrespondstotheuser'sactions.Theseresponsesincludeservicerequestssuchassettingupandtakingdownconnections,andsendingcontrolinstructionsbacktotheEtherphones.Thecontrolserveralsoperformsthetelephone-controlfunctionsusuallyreferredtoascallprocessing.ItprovidescontrolandbookkeepingforconnectionsincollaborationwiththeEtherphoneuserinterfaceprogramsfortheparticipatingparties.Thecontrolserverprovidesaccesstoanumberofdatabases,includingdirectoriesestablishingtherelationshipsamongEtherphonenetworkaddresses,thenamesofindividualsandservices(suchasthevoicefileserver),telephoneextensions,officelocations,andnearbyworkstations.Thecall-processingportionofthecontrolserverhasanadditionalfunction:itsynchronizestheactivitiesofeachEtherphonewiththeworkstationapplicationsthatmanagethatEtherphoneandthatuseittoprovidetheirvoiceconnections.WhenuseractionscomingfromtheEtherphoneandfromtheworkstationsareinconsistent,theserverresolvestheconflicts.Thetelephonecontrolserverincludessomemaintenancefacilitiesnotdirectlyconnectedwithsystemoperation.Forexample,theservercontainssoftwaretodetectthedistresspacketsthatEtherphonesbroadcastwhentheyarepoweredonorwhenunrecoverablefailuresoccur.ThiscaretakersoftwarerespondsbyperformingautomaticdownloadingandremotemaintenanceofEtherphonesoftware.ByXEROXPARC,CSL-83-8,AUGUST,1983wî ìïg/xîèïg/î"ßî%ùî'Rî(ßî,7î1u{î ìï_/îñîbî= î&Ÿî*7î/×î6î;¤î>ðîE`î ìï\û îî´îî ®ïZÆîÉî’ îÚîÖî!y î)=î*ì î1.î3 î8oî;_ îCéî ìïX’ îdîîÿîº î'Gî)ªî.‚î0@î4î5Áî:üî<üîB+îGî ìïV]î ºî É îÛ îzî Oî"Îî)Cî+€î- î1ýî5èî9Cî; î=¯îCuîFwîHeî ìïT)î’ î\î¼ î"<î$èî)ôî+ î1« î8›î ®ïQôîþî> îÍîPî!9î$Lî/!î3î=î>ÏîAŠ î ìïOÀ îöî³îì îõî"]î$] î*Âî0­î2Iî51î6ù î? îB!îEwî ìïM‹î—î™îNî+îßî‘î{î 0î$Üî&±î)î-Wî0çî3Žî:î=zîAºîDî ìïKWî ·îdî î´î&î î&¦î(gî,±î2î3Ûî9Éî=�îBîH#î ìïI"î gîTî î0 î#£î&Aî+î/î3¬î5V î=ÆîBuîEåî ìïFîîZ î î>î´î#_î%àî*î-Úî0“î6/î8Bî:Îî<žîB.îHî ìïDºî KîµîÁî-î|îxî× î$X|î ìï@Þî )î×îá{î 4ï=îîgîî*î%î'jî-kî3= î9¬î<Èî?*îDÜî ìï:Î îfî,îm îžîî ßî'Lî-xî1¼î8î=Aî>¯îAöîDƒîGàî ìï8™îGî-î±îsîNîÏî óî$¨î)/î*¦î-=î/dî4î:+î>.îAîFuî ìï6eîÌî¾îîÉî ìî"Þ î(òî+âî2Oî7î;=î@¡îCeîGÖî ìï40 îd îä î-î!äî$o î ®ï1üî�îgîŠîî | î( î/sî5î7é î>*îA;îEïîGžî ìï/Ç î¶î1 î(î aî#lî%¾î+Kî0î5î7Œî8¨î<8î@ÝîC†î ìï-“î �î”îÍî’î²îòî›î$5î'Dî-î0Êî2 î9‰î; î=• îC½îE¢î ìï+^î "îÃî¿î' î!@î#çî)œî+:î-‰î1Mî61î:"î@:îE î ìï)*îYî îbîÝîîÐî"î%ò î-ßî0«î5Õî:� îBîElîG/î ìï&õ î ®ï$Áîfîùîæî“î Oî"�î-mî3Lî7ßî=î>�î@îB‰ î ìï"�î _îéî—îI î iî"¢ î*î+Ç î4î7î9y î@õîCéî ìï Xî&îŠî î1î"î%î)÷î.*î3àî8î9éî;:î@�îBlîE˜î ìï$î î× îaî Õ î(íî-ˆ î5î:‰ îA îC}îGÖî ìïï îîî¡î§îNîøî Sî#âî&Gî+!î1s î8jî<; îBJîDýî ìï» î&îóîî"èî$–î&êî+’î/“î1üî3á î:Mî@5îA€ î ìï†î o î8îîj îî"Lî$Ð î,\ î4î7îî9 î;ú îCvîF(î ìïî K î9î� îeî Äî$Ñî)üî,[ î ®ïéîrî´îSîLî#œî' î/ î4[î6¼î;�îB îEî ìïµ î£î„î‹î î bî%ûî+ªî-Žî1Òî4gî9qî>†îAŠ î ìï €îCî%îaîáî¨î!Ûî#Ìî'­ î0»î5Æî:»î>îDî ìï LîØîú îQîÎ î(#î+î/Í î7øî9Ö îA}îGsxîÕï î#Pî'î,Xî1íÿ âTVm$QAddingVoicetoanOfficeComputerNetwork13consultinganotherdatabase,thecontrolservercansupportthesimultaneousoperationofdifferentmodelEtherphonesorEtherphoneswithdifferentsoftwareandcapabilities.Forsystemcontrol,wewereabletotakeadvantageoftherecentdevelopmentofremoteprocedurecallprotocols[Nelson,Birrell].RemoteProcedureCall(RPC)isameansfortransformingthemessage-passingsemanticsofpacket-switchingnetworksintotheprocedure-callformatfamiliartoprogrammers.RPClargelyrelievesapplicationsprogrammersfromanyworriesaboutpacketformats,addressing,reliablecommunication,andsecurity.Thismakesitpossibletodeferdecisionsaboutthepartitioningofadistributedsystemuntilverylateinthedesign.OurtaskwasreducedtoproducinganRPCimplementationfortheEtherphonecontrolprocessor,thenspecifyingtheproceduralinterfacesbetweendifferentsystemcomponents.5.5VoiceFileServerThevoicefileserverusesthestored-voiceprotocoltorecordandplaybackdigitizedvoicesegments.ItrunsonaXeroxDoradoequippedwitha300Mbytedisk.At8000bytespersecond,theresultingvoice-storagecapacityisover8hours.Capacitycanbeexpandedasusagewarrants.Thediskisorganizedsothatstorageisallocatedinonesecondunits.Thispermitsdiskactivityonbehalfofasinglerecordorplaybackoperationtobelimitedtoonecontiguousdisktransferpersecond.Nevertheless,usersoftwarecanspecifytheorderanddurationofvoice-segmentaccessatagrainofonemillisecond.Thisfacilitymakesitpossibletoexperimentwithvoiceediting.Theveryhighnetwork-communicationloadspresentedbymultiplevoice-protocolconnectionspresentaspecialchallenge.Thepresentimplementationiscapableofhandlingabouteightsimultaneoustransfers.Allvoiceisstoredinencryptedform.TheassociatedkeysarestoredbytheEtherphonecontrolserverinadirectoryalongwithinformationgrantingappropriateaccesstoeachvoicesegment.Sinceeachvoicesegmentisstoredonlyonce,regardlessofthenumberofusersgrantedaccess,thefileserverdirectoryalsokeepstrackofthenumberofoutstandingreferencestoeachsegment.Voicestorageisreclaimedautomaticallywhennoreferencesremain.5.6WorkstationapplicationsMostusersoftheEtherphonesystemwillhavebothanEtherphoneandapersonalworkstation.Althoughtherecanbeconflictingrequestsforserviceoriginatingfromtheworkstationandtheuser'sEtherphone,voice-relatedapplicationssoftwareontheworkstationgenerallytakespriorityindecisionmaking.Asanexample,consideranarrivingcall.TheEtherphoneisalwayspreparedtoannouncethecallwitharingingtone,butworkstationsoftwareisfirstgiventheopportunitytorejectthecall,allowtheEtherphonetoringnormally,orchoosesomeotherwaytoannouncethecall.OurgoalsincludebothproducingusefulworkstationapplicationsandmakingtheEtherphonefunctionsavailabletootherprogrammerswhowouldliketoproducevoice-relatedapplications.Forthisreason,theworkstationsoftwareincludesabasicpackageofsupportfacilities,thenanotherlayerofspecificapplicationprogramsthatoperateasclientsofthebasicpackage.XEROXPARC,CSL-83-8,AUGUST,1983xî\ïg/î!Sî$mî%Åî'Rî*ªî/èwîG~ïg/{î ìï_/ îoîfîDîŽî",î&$î(šî-‘î/Û î8 î>!î?ÅîEVî ìï\û îñîµ îºîÔî$zî)óî,ª î 'ïZÆîÇî6î6îRî˜î!†î#)î&î,ƒî.0î0…î4� î<Âî>pîC î ìïX‘î ðî\îFî½î$bî+hî.Ïî3—î5|î7î;Ûî>’ îG/î ìïV]înîîî'åî."î1\î4 î=‚îB_îGàî ìïT( îÑîUîöî  î'Ï î0\î3êî6²î;¬î?µîD7î ìïQô î2îF î {î#\î(ôî,8î0›î2î7‡î9_î=îC$îG/î ìïO¿ îfî%îT îKîÌî#î&-î(Óî*‡î,ëî1˜î4€î7^î:î?WîA îGžî ìïM‹î z îŠîùîŠ î$<î) î/½î3 î9¼îîŽ î&+î+Šî-*î1jî4î7î:@î?ÌîCPî ìïAjî ~î³îÔîîVî{î!«î$áî&%î(Õî-Vî0¶î2Ìî6,î9Ûîwî?›îC�îGËî ìï:Ìî±îØî„îsî#îÏî"y î)hî,Sî1\î3Ïî8¶ îAîDî ìï8˜î �îDî»îˆîWîÿî!Ï î*Óî.øî0©î1êî5Šî7[î: îAÖîEî ìï6cîî=î`îï îîÿî#tî(Iî+î-òî0ùî?ÚîCNî ìï4/î Ïî0 î î!vî&2î'Cî+§ î1ùî4¹î9u îC;îDŽî ìï1ûî ¥îaîBîµ î ü î ®ï/Æî&îàîrî»î�î!î$ûî'ú î.Œî1Ìî4Eî8�î:°î=6 îDÜî ìï-‘îîèî3î%îîA î%ìî+z î2ûî7)î8øîZî?¾îAdîEÁîGgî ìï\ûî ”î$îVî>îËîî$ž î*Ïî-„ î3Ÿî4çî:tî@MîB% î ìïZÆîúîu î¶îy î)«î,Àî/î5jî:î>î@Ð î ìïX’ îˆîXî¥îwîcî!ö î)©î-�î0›î5Ùî;Oî<íî?ì îGRî ìïV] î¾îSîG îÕî!›î%_î)Óî,* î2Kî3üî6Tî9¿î@ îD€îG/î ìïT)î { îYî!îG î#šî%Bî'’î+ î2çî5Žî;’î?ýîD%îF·î ìïQôî Ìî›îñîèîî ®ïO³î“î#îl î«î!Hî'3î)jî.+î4î7Æî9¯ îB& î ìïM~îTî^î îó î ±î#¸î&î,î. î1�î3–î5áî:Tî>„ îG\î ìïKJ îîôîºîëî!Rî"âî%| î+ìî-Ôî0!î2Lî4æî9[î:Öî<ªî>¿îDîEïî ìïIîÖîî4îDî\î%Õî)Í î1Oî7nî9�îÈî@‰îB�îGöî ìï> î†îÖî�îÆî¤î#Ïî%áî(Mî,êî0íî61î<}î>éîC9îDþî ìï;Íî ¡îtîIîîUî!tî$J î-(î1¢î3 î95î÷îD¼î ìï9™ îÐî7îîlî ¨î#sî)Äî0 î2\î6‘î7Îî;tî@ßîBîDæî ìï7dî oî!îYîîLîÿî!Yî&«î(Tî*ûî,¹î.bî2í î9uî:üî>_î@îE|îG/î ìï50î Âî�î îÖîÿ î$¢î*~î- î.úî3Ãî8ïî:³î>~î@»îAåîE xîÕï î#Pî'î,Xî1íÿ¨TVm$‹AddingVoicetoanOfficeComputerNetwork156.StatusandPlansWearecurrentlytestinganinitialsystemusingengineering-prototypeEtherphones.WeareplanningtoinstalladditionalEtherphones,offeringservicetoasizeablesegmentofourlaboratory,inordertotestthevalueoftheenhancedcontrolandmessagecapabilitiesandtoallowCedarprogrammerstodeveloptheirownapplications.Withtheenablingfacilitiesinplace,wearejustbeginningtoexplorethepotentialapplicationsofintegratedvoiceintheofficeenvironment.XEROXPARC,CSL-83-8,AUGUST,1983xî\ïg/î!Sî$mî%Åî'Rî*ªî/èwîG~ïg/zî ìï^õî Èîóî{î ®ïZüî%îfî1î„îbî!;î%£î):î6Ñ î?îA“îCÔî ìïXÇî �î� î÷ îFî#oî'èî)‰î*¦î/¹î5î6ºî98 î@îA»îEbîGî ìïV“î Mî÷î±îî>îòî!ªî' î.!î0Ùî2ˆî63î:L îB³îDcî ìïT_î î îèîQîœî#" î(qî* î-âî/õî24î4Âî;î<³îAˆîCÓî ìïR* î‚î; î³îFîôî!Tî%* xîÕï 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«ï_/îãîÛîî‚îúî$žî ìï\³î «ïZî îmîAî^îÉîî%î'¿î+ðî0Æî6ßî9‚ î@·îE®î «ïXJîÉîˆîÀî&Žî)†î/î1‰î7î:1î ìïUÏî «ïSšîˆîßîîÔîêîéî!>î#•î)Îî,%î-iî9î>¯îFî «ïQfîî•î›î) î'e î0öî3î7@î9©î?"îBRî ìïNê î «ïLµîŸîX î‰îƒ î#õî(ªî-•î0Bî5 î; î=ÖîAîDÒîF—î «ïJ�îèîR î+îxî ìïH î «ïEÑîÈî1îî î<îXî"õ î)Û î1]î5ûî<Šî>ÿîCî «ïCœ îìîaîšî!’î#Ïî&8î+±î.ªî ìïA! î «ï>ìî î%î�îSîÈî¨îã î'£î)[î,~î21î61î9î>âîEWî «ï<·î£îàîJîÂî`î ìï:<î «ï8îŒîºîî¹îçîß î$¶î)e î0~î2· î<î=ºîA¡îGÖî «ï5Ó îÅî;îsî"kî$¨î'î,Šî3.î ìï3Wî «ï1"înîåuîóï1"îðï1"îáî C{î"¸ï1"î#”ï1"î'·î,î0Äî7Pî:€î ìï.§î «ï,rîíîC î™î"»î'y î.‹î4hî8î=îCªî ìï)÷î «ï'ÂîÌî_îÇîšî±î�îð î'Ëî) î10î7„î;ûîBÛîFØî «ï%�îî(îçîî#íî&åî,~î.èî2Oî7{î ìï#î «ï Ýî"îæîoîÚî¼î#Cî(ôî*åî0Œî4Wî: î;ƒî=îB^ î «ï©îéî€îÝî7îDî~î"î(½ î/Öî6bî<ðîAÂ î «ïtîiî ìïùî «ïÄîµîžîîæîÒî»î"&î$íî&áî,­î0Eî38î6˜ î<Çî>Ç îFî «ï�îdî îš î"Fî$¯î*(î-zî ìïî «ïßî³î�înî`îÀ î"-î$î&Šî-î/-î1î6…î9kî;”î=¨îB;îHî «ï«î3 îÄîlî!ó î(gî.^î1î7¡î9–î?ÚîA®îC®îFØî «ï vî�î�î« îŒî"Öî&^xîÕï 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