Mobile Service Applications UMTS

Mobile Service Applications and Performance in UMTS
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Dr.MohitBansal,Canada,Teacher
Published Date:26-10-2017
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MobileServiceApplicationsand PerformanceinUMTS Thepurposeofthischapteristointroducethefunctionalaspectsofcircuit-switched(CS) andpacket-switched(PS)basedservicesandtheirperformanceoverUniversalMobile TelecommunicationSystem(UMTS). Theconvergencephenomenonthatstartedsomeyearsagoandthatisacceleratingwill graduallyremovethetraditionalboundariesbetweenfixedandmobilecommunication systems.Inthefuture,personalcommunicationdeviceswillbemultiradio-capablewhile broadband wireless coverage will extend considerably. On the other hand, Internet Protocol(IP)basedservicesareexpandingallthetimeandnowoverlapwiththose providedbyCSsystems,eitherfixedormobile,VoiceoverIP(VoIP)beingoneofthe mostremarkableexamples.Inshort,theglobaltrendisthatcommunicationswillbePS andthatmoreandmoredevicesandnetworkswillsupportwirelessmobility.Getting there,however,willrequireeffortandtime;so,ifthetrendisclear,weshallnotyetignore establishedCSsystemsandservicesastheywillcontinuetohaveakeyroleformany years. Thefunctionalaspectsandperformancerequirementsofmobileservicesareimportant pieces in the overall end-user quality-of-experience management. For instance, the necessaryprocedurestosetupaservicewilldeterminehowlongsessionestablishment willtakedependingontheactualunderlyingnetworktechnology(e.g.,cellularorfixed access network). Also, once the session has been established, there will typically be specificthroughputandlatencyrequirementstofulfil,whichinturnmayimposepar- ticularservicestobeusedonlyincertaintypesofnetworks.Asanexample,someaction gamesmaybewell-supportedinwidebandcodedivisionmultipleaccess(WCDMA)but notintheGeneralPacketRadioService(GPRS)becauseoftoolonglatencies. Evaluatingtheoverallserviceperformanceinagivenlow-tomedium-loadednetwork maybeonestartingpointwhenconsideringthelaunchofanewservice.Iftherequired performanceisnotfulfilled,eveninthebestconditions,itisprobablynotworthmoving ontothenextphaseofservicedeployment.Atthesametime,itisimportanttonotethat10 QoSandQoEManagementinUMTSCellularSystems lowserviceperformancemaynotalwaysbeduetonetworklimitations,butmayalso,for instance,beduetolessthanoptimalterminalorserverimplementations.Incertaincases, optimising the application or the transport layer or applying, for example, efficient header or data compression mechanisms may be enough to achieve satisfactory quality-of-experiencelevels. ThischapterconcentratesmostlyonPSservices.ThemainreasonbeingthattheCS service’sfunctionalaspects,requirementsandperformanceinUMTShavealreadybeen widelydocumentedelsewhere(e.g.,1).Thus,Section2.1summarisessomekeypointsin theareaandlargelyreferstoothersources.Theremainingsections–Sections2.2and 2.3– focussolelyonthePSservice’sfunctionalaspects,requirementsandperformance inUMTS. 2.1 CS service applications TheUMTSnetworkarchitectureislogicallydividedbetween2theradioaccessnetwork (RAN)andthecorenetwork(CN).TheCNisitselfseparatedintothePSCNdomain, theCSCNdomainandtheIPmultimediaCNsubsystem(IMS)(seeChapter3).TheCS domain is an evolution of the Global System for Mobile Communications (GSM) technologythatwasdevelopedundertheEuropeanTelecommunicationStandardInsti- tute (ETSI) until 2000, and pursued later in the 3rd Generation Partnership Project (3GPP)standardisationbody.InCSsystems,resourcesareallocatedatservicesession setupandreservedduringtheentiresessionduration.Thisapproachiswell-suitedfor applications, such as (multimedia) telephony, that have stringent and stable require- mentsintermsofdelayandbandwidthandwhentrafficsourcesaresendingorreceiving dataduringthemajorityofthesession.PSsystems,ontheotherhand,canefficiently support any type of service applications, including those that may be very bursty in nature,andpossiblyidleagreatpartofthesession(e.g.,webbrowsing),bydynamically allocatingnetworkresourcesonaneedbasis. 2.1.1 CStelephony CStelephonyisspecifiedin3togetherwithotherservices–suchasemergencycalls, ShortMessageService(SMS). Speech codecs for mobile communications have improved over the years bringing significantgainsbothintermsofspeechqualityandcapacity.Theadaptivemultirate (AMR)consistsofafamilyofcodecswithdifferentbitratesoperatinginGSMfull-rate (FR)andhalf-rate(HR). AMR speech codec (adopted in 3GPP R99 as a mandatory codec) performance is characterisedin4:unlikepreviousGSMspeechcodecs(full-rate,enhancedfull-rateand half-rate)thatoperateatafixedrateandataconstanterrorprotectionlevel,theAMR speechcodeccanadaptitserrorprotectionleveltotheradiochannelandtrafficcon- ditions.AMRselectstheoptimalchannel(half-orfull-rate)andcodecmode(speechand channelbitrates)todeliverthebestcombinationofspeechqualityandsystemcapacity. Thisflexibilityprovidesanumberofimportantbenefits:MobileServiceApplicationsandPerformanceinUMTS 11 25 Channel coding 20 Speech coding 15 10 5 0 FR FR FR FR FR FR FR FR HR HR HR HR HR HR 5.15 5.15 4.75 12.2 10.2 7.95 7.4 6.7 5.9 4.75 7.95 7.4 6.7 5.9 Figure 2.1 AMRcodecmodes. . Animprovedspeechqualitybecauseofcodecmodeadaptation,byvaryingthebalance betweenspeechandchannelcodingforthesamegrossbitrate. . Theabilitytotradespeechqualityandcapacitysmoothlyandflexiblybyacombina- tion of channel andcodec mode adaptation; this can be controlled by the network operatoronacell-by-cellbasis. . Improvedrobustnesstochannelerrorsundermarginalradiosignalconditionsinfull- ratemode.Thisincreasedrobustnesstoerrorsandhencetointerferencemaybeused toincreasecapacitybyoperatingatighterfrequencyreusepatterninGSM. . AbilitytotailorAMRoperationtomeetthedifferentneedsofoperators. . Potentialforimprovedhandoverandpowercontrolresultingfromadditionalsignal- lingtransmittedrapidlyin-band. The AMR codec concept is adaptable not only in terms of its ability to respond to changingradioandtrafficconditionsbutalsotobecustomisedtothespecificneedsof networkoperators.TheAMRcodecmodesareillustratedinFigure2.1. WidebandAMR(AMR-WB)wasintroducedin3GPPR5andprovidesfurtherspeech quality enhancements that are essentially due to the larger speech-coding bandwidth (from50to7000Hz).TheseimprovementsmakeAMR-WBalsosuitableforapplica- tionshavinghigh-qualityaudiorequirements. 2.1.2 CSmultimediatelephony Therequirements formultimediaCScallsaredefinedin3GPP5.Someofthese are providedbelow: . CSmultimediaisbasedonanInternationalTelecommunicationUnion(ITU)H.324 terminal. . All call scenarios are supported: mobile-originating and mobile-terminating call, against a mobile Integrated Services Digital Network (ISDN) or Public Switched TelephoneNetwork(PSTN)callparty. . Singleandmultiplenumbering. Channel bit rate (kb/s)12 QoSandQoEManagementinUMTSCellularSystems . Ifthesetupofthemultimediacallfailsthecallwillbesetupasaspeechcall. . In-callmodification:modificationofcalltypefromspeechcalltomultimediacall(and vice versa)duringthecall.Servicedegradationandupgrading. . End-to-enduserratenegotiation. . H.324andH.323(forPSmultimedia)interworking. H.324consistsoftwomandatorycomponents6:H.223formultiplexingandH.245for thecontrol.OtheroptionalcomponentsareH.263videocodec,G.723.1speechcodec andV.8bis.MPEG-4videoandAMRwerelateraddedtothesystemasoptionalcodecs. CSvideoqualityismoresensitivetotheblockerrorratethanvoiceduetothenatureof videocompressionand,thus,theallowedresidualbiterrorrateistypicallyverysmall 5 (e.g.,10 )toensureagoodqualityofexperience6. 2.2 Packet-switched service applications BeforegoingintothedetailsofPSservices,itisworthintroducingverybrieflytheIMS whichisdescribedinmoredetailinChapter3.TheIMS,addedin3GPPR5,containsall CN elements needed for providing multimedia (IP-based) services 7, 8. The IMS enables operators to offer subscribers multimedia services based on and built upon Internet applications, services and protocols. The Session Initiation Protocol (SIP) is theapplicationlayercontrolprotocolusedforestablishing,modifyingandterminating peer-to-peerservicesessions9.Apeer-to-peerservicesessioncouldbeasimpletwo-way telephonecall,acollaborativemultimediaconferencesessionor,forinstance,anetwork game.SIPisanInternetEngineeringTaskForce(IETF)drivensignallingprotocolbased ontherequest–responseschemesimilartoHypertextTransferProtocol(HTTP)signal- ling. 2.2.1 Browsing ThebrowsingserviceallowsamobileusertobrowsetheWebbyusingabrowserinstalled onamobilephone.TheusermayeithertypeinaURLorclickalinkinordertoaccessa webpage. TheOpenMobileAlliance(OMA)browsingenablerisbasedonWirelessApplication Protocol (WAP) standards from the WAP Forum and is migrating towards Internet protocols. Hence, depending on the software implemented, a mobile phone may use: . HTTP1.1tocommunicatedirectlywithawebserver10; . WirelessProfileHTTPtocommunicatewithaWAP2.0gatewaythatinturncontacts awebserver11;or . WirelessSessionProtocol(WSP)tocommunicatewithaWAP1.0or2.0gatewaythat inturncontactsawebserver12. AllthreeprotocolsarebasedontheHTTP1.1requestandresponseparadigm10.As showninFigure2.2,awebpageisrequestedbysendingaGETrequestmessagetoaweb server(oraWAPgatewaythatinturnsendstherequesttotheserver).IftheoperationisMobileServiceApplicationsandPerformanceinUMTS 13 Browser User A Server Request for a page GET request (for the main page) GET response (the main page) GET request (for an embedded object) GET response (an embedded object) Page displayed to user GET response (last embedded object) Figure 2.2 Browsingservicemessageflows. successful, the web server will reply with a GET response message that contains the requestedwebpage.Awebpagemayhavemultipleembeddedobjectssuchasimages,in whichcaseeachobjectisfetchedwithaseparateGETrequestmessage.AGETresponse messagefromawebservercontainsastatuscodetoindicatetheresultoftheoperation. 2.2.2 MultimediaMessagingService(MMS) The MMS is a system application by which a client is able to conduct messaging operations with a rich set of media contents, such as image, video, etc. MMS is a non-realtimedeliverysystem,thoughitisexpectedthatamultimediamessageshould be deliverable within a reasonable time frame. MMS can interoperate with other messaging systems – such as the traditional email on the Internet. In other words, whenoneendpointoftheserviceisanMMSclient,theotherendpointforthemultimedia messagemaybeanotherMMSclient,aclientonalegacywirelessmessagingsystemoran emailclient.MMSisspecifiedinOMAin13–16. AnMMSproxy-relayisanetworkelementthatinteractswithMMSclientsonmobile phonestoprovideMMSservices.Inaddition,itprovidesaccesstoanMMSserverthat storesmessages.Furthermore,italsoservesasagatewaywheninteractingwithother messaging systems (e.g., Internet email). Some implementations may combine MMS proxy-relayandMMSserverintoonephysicalelement. TherearetwowaysamessagemayberetrievedbyareceivingMMSclientdepending onserviceprofilesand/ordevicesettings.Immediateretrievalofanewmessagemeans thatareceivingMMSclientimmediatelyretrievesthemessageviatheMMSproxy-relay uponreceivinganewmessagenotification.Incontrast,deferredretrievalmeansthata receivingMMSclientfirstacknowledgesanewmessagenotificationandatsomelater pointretrievesthemessageviatheMMSproxy-relay. Figure2.3showstheMMStransactionsforimmediateretrieval.Inthefigure,boththe origination and termination points are MMS clients. The MMS protocol data unit (PDU)canbecarriedbyeitherWSPorHTTP.Themessagenotification(M-Notifica- tion.ind)issentviaWAP. Service response time14 QoSandQoEManagementinUMTSCellularSystems Orig. MMS Term. MMS UE A UE B User A User B proxy-relay proxy-relay Compose message M-Send.req Click send M-Send.conf Interactions across network Message stored at MMS server M-Notification.ind WSP/HTTP GET.req M-retrieve.conf. Notify user M-NotifyResp.ind Notify user if report requested Interactions M-Delivery.ind across network Figure 2.3 MMSwithimmediateretrieval. Afterausercomposesamessage,he/sheclicksthesendbuttononthemobilephone. The MMS client transmits the message to the MMS proxy-relay. Upon receiving the messagewithnoerror,theMMSproxy-relaysendsbackaconfirmationtotheMMS client. The multimedia message is then forwarded across the mobile network to the terminatingMMSproxy-relayandisstoredinitsassociatedMMSserver.Theterminat- ingMMSproxy-relaythennotifiestheoriginatingMMSclient. For immediate retrieval, the MMS client tries to fetch the message with a GET operation.Afterthemessageisretrieved,theMMSclientsendsaNotifyresponseback totheMMSproxy-relay.ThisresponseisforwardedtotheoriginalMMSproxy-relay, whichthensendsadeliveryindication(M-Delivery.ind)totheoriginatingMMSclientto acknowledge the status of the message delivery. If the user has requested a delivery report,theMMSclientwillinformtheuseruponreceivingtheM-Delivery.ind.Other- wise,theuserisinformedonlywhenthedeliveryisnotsuccessful. For deferred retrieval, a receiving MMS client responds to a message notification immediately.Butthemessageisnotretrieveduntilalatertime–forexample,whenthe useraskstoreadthemessage. Dependingontheservicesettingsonthereceivingmobiledevice,sendingofadelivery reportbacktotheoriginalusermaybedenied.Inotherwords,theoriginalMMSclient cannotassumethatadeliveryreport(M-Delivery.ind)isguaranteedforeverymessage sent. Service response timeMobileServiceApplicationsandPerformanceinUMTS 15 2.2.3 Contentdownload OMAisdefiningagenericcontentdownloadover-the-airspecification17.Asspecified, a download user agent is an agent or software function in the device responsible for downloadingamediaobject.Adownloaddescriptorcontainsinformationaboutamedia objectandinstructionstothedownloadagentabouthowtodownloadit.Itallowsthe clientdevicetodecidewhetherithasthecapabilitiestoinstallandrender/executethe mediaobject. TheOMAspecificationsupportstwoscenarios: . Downloadwithseparatedeliveryofdownloaddescriptorandmediaobject. . Downloadwithco-deliveryofdownloaddescriptorandmediaobject. Inbothscenarios,thedownloadagentmaysendanotificationtotheserverinorderto confirmthestatusofthetransaction.Thisnotificationislikelytobemandatoryinapay- per-transaction model where the confirmation of a successful installation of a media objecttypicallytriggersserver-endbillingactions. Figure2.4showsthemessageflowsforaseparatedeliveryofdownloaddescriptorand mediaobject.Auserisinitiallypresentedwithareferencetothedownloaddescriptor. Thereferencemaybeonawebpage,insideanemailoranMMSmessage,orstoredin memory. Iftheuserhastheintentionofpursuingthedownload,he/shewillclickthereferenceto obtainthedescriptor.Thedownloaddescriptoristhentransferredtothemobiledevice. ThetransfermechanismorprotocolmaybeHTTPorsecureHTTP(HTTPS)butcan alsobethroughMMS,emailorsomeinstantmessagingprotocol.Thedownloadagent Download agent User Server Fetch descriptor Fetch descriptor Descriptor Verification Notify user Validate the action Retrieve media Download media Pre-installation Notification Confirmation Figure 2.4 Separatedeliveryofdownloaddescriptorandmediaobject. www.allitebooks.com Service response time16 QoSandQoEManagementinUMTSCellularSystems usestheinformationinthedescriptor(e.g.,mediatypeandsize)tocheckwhetherthe deviceiscapableofusingorrenderingthemediaobject.Ifthedeviceisabletohandlethe mediaobject,theuseristhenpresentedwithmoredetailedinformationaboutthemedia (type,size,vendor,etc.)andisaskedtoconfirmthatsheindeedwantstodownloadand installthemediaobject.Onconfirmationfromtheuser,themediaobjectisretrieved, typically using HTTP or HTTPS, according to the instructions from the download descriptor.Thedevicethentriestopre-installthemedia.Ifaninstallationnotification hasbeenrequestedinthedownloaddescriptor,thedevicepreparesthemediaobjectfor renderingorexecutiontothelargestextentpossiblewithoutactuallyallowingittobe used.Thisistoensure,asmuchaspossible,thatthemediacanbeinstalledandconsumed bytheend-userwithouterror.Itthensendsaninstallationnotificationtotheserverto report the outcome of the previous step. A set of status codes to be included in the notification is defined in 17. If the installation notice is successfully sent, the media objectwillbemadeavailableforexecutionandtheuserisnotifiedwithaconfirmation. Otherwise,themediaobjectwillberemovedfromthedevice. Different servers may provide the downloaddescription and the media object. The mobileagentmaysendthenotificationtoyetanotherserveraccordingtothedownload descriptor. Inco-deliveryofthedownloaddescriptorandmediaobject,whenanend-userrequests adownload,thedownloaddescriptorandthemediaaredeliveredtogethertothemobile device.Theremaininginstallationandnotificationprocessesarethesameasdescribed above. 2.2.4 Streaming Thestreamingservicedescriptionbelowfollowsthe3GPPtransparentend-to-endPS streaming service specification 18–20. A streaming service contains a set of one or morestreamspresentedtoauserasacompletemediafeed.Thecontentistransported using Real time Transport Protocol (RTP) over User Datagram Protocol (UDP). Control for the session setup and for the playing of media (PLAY, PAUSE) is via theRealTimeStreamingProtocol(RTSP)21. Figure2.5showsthestreamingservicemessageflows.Whenauserstartsastreaming servicebyeitherclickingalinkinawebpageorenteringauniformresourceidentifier (URI) of a streaming server and content address, the streaming client on the mobile phonemustfirstobtainapresentationdescriptionthatcontainsinformationaboutone ormoremediastreamswithinapresentation,suchasencoding,networkaddressesand information about the content. This presentation description may be obtained in a number of ways – for example, via MMS or RTSP signalling. 3GPP mandates that thedescriptionbeintheformofaSessionDescriptionProtocol(SDP)file22. Oncethepresentationdescriptionisobtained,thestreamingclientestablishesasession for each media stream. Specifically, it may try to establish a secondary PDP context (depending on UE capabilities) for each streaming media and also sends a SETUP request message to the media server in order for the server to allocate resources for the stream. The SETUP reply message contains a session identifier, server port for displaying the media and other information required by a client for playback of the mediastream.MobileServiceApplicationsandPerformanceinUMTS 17 User Streaming client Server SGSN Click URI Fetch SDP file SDP file SETUP request SETUP response First media setup Secondary PDP context activation request Secondary PDP context activation accept Continue media sessions setup All sessions setup complete Ready to play Click play button PLAY RTP/UDP content Stop or cancel TEARDOWN request TEARDOWN response Secondary PDP context deactivation request Continue media sessions tear down Figure 2.5 Streamingservicemessageflow. AfterallmediastreamsessionsandtheirrequiredPDPcontextsareestablished,the usermayclicktheplaybuttontostartplayingthesynchronisedmedia.Theusercanalso pause,resumeorcancelthestreamingserviceatanytime.TheRTSPPLAY,PAUSEand TEARDOWNmessagesaresenttotheserverforthecorrespondingaction. 2.2.5 Gaming Gamingservicesallowend-userstoplaygamesonmobiledevicesovermobilenetworks. A solo game is a game where a single game player interacts with a game server. A multiplayer gameisagamewheremultipleplayersareinvolved.A person-to-person game isagamewheretwoormoreplayersinteractwitheachotherwithouttheinterventionof a game server. A server-based game has a game server that is responsible for game Service response time18 QoSandQoEManagementinUMTSCellularSystems synchronisationbetweenplayers,updatingthegamestatustoallplayers,keepinghigh scores,etc. Therearealreadymanymobilegamesoutthereandnewgamesarebeingreleased everyday.Eachgameisdifferentwithitsowngamelogic,sessionmanagement,etc.In addition,differenttypesofgameshavedifferentend-userrequirements23.Forexample, arealtimeshootinggamewouldhavemorestringentrequirementsthanaturn-based game such as chess. Furthermore, game applications may run on top of different transportprotocolssuchasHTTP,TCP,UDP,SMS,WAPpush,etc. WenotethatOMAisworkingongamingservicestandardisation.Theworkinggroup hasbeenspecifyingagamingarchitecture24,aserverframework25andaclient/server protocol26.Theclient/serverprotocolisinitsveryearlystageandisnotcompletely consistentwiththeotherOMAgamingspecifications. Inmultiplayergames,sincenoteveryplayerissuitedtomatchwitheveryotherplayer, prospectiveplayersneedaplacetomeetandstageagame.Alobbyissuchaplace.There canbemanylobbiesforaspecificgame.Agameroomiswhereagameisactuallyplayed andtherecanbemanygameroomsinalobby.Dependingonthedesignofagame,a playermayormaynotbeallowedtocreateanewlobby.Aplayercanjoinanexisting gameroom,orcreateagameroomtostartanewgame.Bothlobbiesandgameroomsare infactmulticastinggroupswhereamessageoramoveisbroadcasttoallmembersinthe group. To play the game, the player must first connect to a game server, log in and be authenticated.Then,he/shecanbrowsethelistoflobbies,enteraspecificlobby, join anexistinggameroomorcreateanewgameroom,andplayagame. 2.2.6 Businessconnectivity Businessconnectivityisaboutenablingend-userstoaccesscorporateIntranetorInternet services from a wireless device, in a secure manner. The access network may be, for instance,EGPRS,WCDMAorWLAN.Theend-userdevicemaybeasmartphoneora laptop. Securitycanbeensuredwithavirtualprivatenetwork(VPN).Forlargeenterprises thatseekend-to-endsecurity,aclientVPNisneededinthemobiledevice.Smallcom- panies may on the other hand decide that encryption between the mobile operator’s domainandtheirenterprise’sdomainissufficient. ThesecuritycanbeofferedthrougheitherIPsecurity(IPsec)protocols27–30orthe secure socket layer (SSL) 31 protocol. In this section we only consider IPsec-based VPN. IPsecVPNprotectsIPpacketsbyoffering: . Packet confidentiality–packetsareencryptedbeforebeingsentoverthenetworkso thatonlyauthorisedentitiescanreadthem. . Packet integrity–packetsareprotectedsothatanyalterationsduringtransmission overthenetworkcanbedetected. . Packet origin authentication–packetsareprotectedtoensurethattheyareindeedfrom the claimed sender whose IP address is contained in the source address of the IP header.MobileServiceApplicationsandPerformanceinUMTS 19 . Protection against replay–packetsareprotectedfrombeingcapturedandre-sentat somelatertime. The above protections are achieved through the use of one or a combination of two securityprotocols:theencapsulatingsecuritypayload(ESP)29andtheauthentication header(AH)30.NotethatAHalonedoesnotprovideconfidentialityprotection. Therearenetwork-basedandclient-basedVPNservices.Inanetwork-basedservice,a secure IPsec tunnel is established between a security gateway at the Gi interface and anothergatewayatthecorporatenetworkpremises.TheIPsectunnelthusprotectsdata whentheytravelthroughtheInternet.Inaclient-basedservice,apieceofVPNsoftware, referredtoasthe‘VPNclient’inthefollowing,isinstalledonamobiledevicetogether withtheIPsecVPNpolicy.TheclientcreatesIPsectunnelsbetweenthemobiledevice andthesecuritygatewayatthecorporatenetworkpremises,accordingtotheinstalled VPNpolicy.Thetunnelsoffersecurityprotectiontopacketsthattravelthroughit.In addition,dictatedbytheVPNpolicy,theclientcanalsodropincomingand/oroutgoing packets.Forexample,ifareceivedpacketdoesnotpassdataauthentication,itwillbe droppedbytheVPNclient. InordertousethemobileVPNservice,VPNaccesspointshavetobeconfiguredon mobiledevices.EachaccesspointmustalsohaveareferencetotheVPNpolicy.VPN accesspointscanbeusedinthesamewayasanyotheraccesspoints. AsshowninFigure2.6,toaccessenterpriseservicesfromamobiledevice,anend-user simplyactivatestheserviceinthesamewayaswhenusingotherservices.Whenbeing askedtoselectanaccesspoint,theuserchoosesaVPNaccesspoint.Themobiledevice firstestablishesthePDPcontextforInternetaccess.Then,itnegotiates,accordingto theVPN policy associatedwiththeVPN accesspoint,withasecurity gatewayatthe enterpriseinordertoestablishasecuretunnel.Theprocessincludestwophases:Phase1 iscalled‘Internetkeyexchange(IKE)’andPhase2involvesnegotiations28.Inthefirst phase,thetwoendsagreeonencryptionandauthenticationalgorithmsforasecureIKE tunnel,authenticateeachotherandderivesecuritykeysforencryptionandauthentica- tion.Phase1negotiationmayinvolveeitherthreeorsixInternetSecurityAssociation andKeyManagementProtocol(ISAKMP)messageswithdifferentpayloadsdepending onwhetheraggressiveormainmodeisused.Whenthisphasebegins,theuserisalso askedtoprovideauthenticationinformationtobeusedinPhase1negotiation.Itcanbea staticpasswordorasecure-idpass-code.Theauthenticationinformationisexchangedin thelasttwomessagesofIKEPhase1negotiation.Dependingontheconfiguration,the gatewaymayuseaRadiusserver,aninternaldatabase,aLightweightDirectoryAccess Protocol (LDAP) directory or something else to handle the authentication requests receivedduringIKEPhase1negotiations.AttheendofPhase1negotiation,anIKE tunnelissetup. IKEPhase2negotiationisconductedundertheprotectionoftheIKEtunnel.The secondphaseaimsatestablishingtwounidirectionalIPsectunnels,basedoneitherESP, AHoracombinationofboth,toprotectserviceorapplicationtraffic.Anditisthese IPsectunnelsthatprovideconfidentiality,integrity,authenticationandreplayprotec- tions of application traffic to and from corporate networks. The second phase of negotiationtypicallyconsistsofthreeISAKMPmessages.AftertheIPsectunnelsare20 QoSandQoEManagementinUMTSCellularSystems Gateway Enterprise server Mobile device SGSN User Access enterprise service Request AP selection Select VPN AP Activate PDP Context Req. Activate PDP Context Ac. Request authentication ISAKMP ISAKMP Submit authentication ISAKMP IKE Phase 1 ISAKMP ISAKMP ISAKMP ISAKMP IKE Phase 2 ISAKMP ISAKMP Secure tunnel is established Service request Service response Closing VPN AP Deletesecurityassociation Delete security association Secure tunnel is torn down Figure 2.6 MobileVPNservicemessageflow. established,legitimatedatatrafficcantravelbetweenthemobiledeviceandthecorporate network.Thesecuritytunnelscanbeclosedwhentheyarenotneeded. During thelifetimeof the IPsectunnels, aVPN client can alsodropincoming and outgoingpacketsaccordingtothesecuritypolicy.Forexample,outgoingpacketsthat aredestinedtothecorporatenetworkbutarenotsupposedtobecarriedbytheIPsec tunnel,accordingtothepolicy,aredropped.Incomingpacketsthataredamagedduring thetransmissioncannotpassdataauthenticationandhencearedropped. 2.2.7 PushtotalkoverCellular(PoC) PoCenablesarealtimeone-to-oneandone-to-manyvoicecommunicationserviceina cellularnetwork.Userscanselectthepersonortalkgrouptheywishtotalkto,andthen pressthepushtotalk(PTTorPoC)keytostarttalking.Thecallisconnectedinrealtime. PoCcallsareone-waycommunication:whileonepersonspeaks,theother(s)onlylistens. Function duration Service response timeMobileServiceApplicationsandPerformanceinUMTS 21 User A PoC Client A PoC Server PoC Client B User B Press PTT key Talk burst request Receiving talk Display active Permission to talk burst Talk burst confirm user info tone Speech Talk burst Release PTT key complete Remove active Talk burst ends user info Talk burst Press PTT key Receiving talk request burst Permission to Display active user Talk burst confirm talk tone info Speech Talk burst Release PTT key complete Remove active user Talk burst ends info Figure 2.7 PoCservicerequestsandindications. TheturnstospeakarerequestedbypressingthePTTkeyandaregrantedonafirst- come-first-serve basis. Hence, if User A has requested to speak prior to User B, the requestfromUserBgoestoaqueueandaqueuingtoneisgiventoUserBtoindicatethat thefloorwasgrantedtoanotheruser,ifqueuingissupportedbythePoCclientofUserB. TheusershouldreleasethePTTkeyandwaitfortheotherpersontofinish.Ifhestill wantstotalktothegroup,hemustpushthePTTkeyagain.Atthereceivingend,thePTT speechisconnectedwithouttherecipient(s)answeringandisheardthroughthephone’s built-in loudspeaker. The receiving user may respond to the call by pushing the PTT button. Whilepopular,PoCisanevolvingserviceintermsoftechnology,standardisationand servicefeatures.ThefollowingdescriptionisbasedontheOMAPoCarchitecture32. Figure2.7showsthePoCrequests/responses/indicationsmessageflowsfollowingthe OMAPoCarchitecture32document.Inpractice,theremaybemultiplePoCservers involvedthatperformdifferentfunctions–forexample,handlingsignalling,distributing themediastream,etc.Forsimplicity,onlyonePoCserverisshowninthefigure. WhenauserpressesthePTTkey,atalkburstrequestissentbythePoCclienttothe PoCserverinordertorequestpermissiontosendatalkburst.Therequestcontainsa PoCsessionidentifierandanindicationonwhetherqueuingissupportedbythePoC client. Service response time User reaction time22 QoSandQoEManagementinUMTSCellularSystems ThePoCservergrantsthefloorbysendingatalkburstconfirmresponsethatcontains thesessionidentifier.IfthePoCservercannotgrantthefloor,atalkburstrejectresponse is sent to the PoC client. The rejection response contains the session identifier and a rejectionreason.Thereasonmaybe: . another PoC client has already been given permission to send a talk burst and no queuingoftherequestisallowed; . another PoC client has already been given permission to send a talk burst and the queueisfull. . thePoCclientisnotallowedtorequestpermissiontosendatalkburstatthemoment; and . onlyoneparticipantinthePoCsession–forexample,ifonlyoneparticipantisleftina PoCsession(hencenooneislistening) IfthePoCserverandthePoCclientsupportqueuingofthetalkburstrequestandthe particular request is queued, the PoC server sends back a talk burst request queued responsetoindicatethattherequestisqueued.TheindicationincludesthesessionID andthepositionatwhichtherequestisqueued. Attheendofatalkspurt,theuserreleasesthePTTkeyandatalkburstcompleted indicationissenttothePoCservertoindicatetheendofthetalkburst.Theindication alsoincludesasessionID. Attheterminatingend,whenthePoCservergrantsthefloortooneclient,itsendsa receivingtalkburstindicationtoalltheotherPoCclientsinaPoCsessioninorderto informthemthatanotherPoCclienthaspermissiontosendatalkburstandthatthePoC clientsmustbepreparedforreceivingatalkburst.Thereceivingtalkburstindication includesaPoCsessionidentifierandtheidentityofthePoCparticipantatthePoCclient sendingthetalkburst–thatis: . thePoCaddresswhenthesenderdoesnotwanttobeanonymous;and . thedisplaynameofthePoCparticipantatthePoCclientsendingatalkburst. ThePoCclientdisplaysthenameofthePoCparticipanttothePoCclientsendingatalk burst. ThePoCservercanalsorevokethepermissiontotalkbysendingastoptalkburst indicationtothePoCclient.Thepossiblereasoncanbe,forexample,thereisonlyone userinthePoCsession(hencenooneislistening)orthetalkburstistoolongandhas exceededthemaximumdurationallowed.ThestoptalkburstindicationincludesaPoC sessionidentifierandmayincludeareasoncodeandaretry-aftertimevalueindicating how long the PoC client has to wait before a request to send a talk burst will be confirmed. This parameter is only present when permission to send a talk burst is revokedduetothetalkburstbeingtoolong. 2.2.8 Videosharing(VS) VSisdefinedasapeer-to-peer,unidirectional,PSmultimediastreamingservicewhereat leastoneoftheactorsisusingamobiledevice.InVS,videofromalivecameraoraMobileServiceApplicationsandPerformanceinUMTS 23 RTVS Client A User A IMS RTVS Client B User B Req to share video INVITE 100 Trying INVITE 183 Session Prog 183 Session Prog PRACK PRACK 200 OK 200 OK Resource reservation Resource reservation UPDATE UPDATE 200 OK 200 OK Video offer 180 Ringing 180 Ringing Remote alerting PRACK PRACK 200 OK 200 OK Accept Remote accepted 200 OK 200 OK ACK ACK Video Disconnect BYE BYE Remote disconnected 200 OK 200 OK Stop RTP/RTCP Release resources Figure 2.8 Videosharingservicemessageflows. multimedia file stored in the originating device is sent to a destination device. The multimediadataarestreamedfromonedevicetotheotherandareconsumedinreal time,creatingtheexperienceof‘sharingthemoment’.OneusecaseforVSistoenricha CS voice call by sharing live video or pre-recorded video clips during the voice call. ThoughtheVSserviceisnotbeingstandardised,implementationmayfollowthe standardIMSspecification7thatemploysSIP9asitssessionmanagementprotocol. Video media are carried by RTP, and RTCP is used to provide video performance feedbacksinordertoadjustmediadeliveryaccordingtonetworkconditions. Figure2.8showsapossiblemessageflowforVS.TheVSclientinthefigurerepresents allthesoftwarefunctionsonamobiledevicethathandleVSapplications.DuringaCS Service response time24 QoSandQoEManagementinUMTSCellularSystems voicecall,UserAwouldliketosharevideocontentby,forexample,selectinga‘share video’button.TheVSClientAinturnsendsaSIPINVITEmessagethatcontainsallthe codecsthataresupportedbythedevice.TheVSClientBanswerswitha183Session Progressmessagethatcontainsallthecodecsitsdevicesupports.Then,ClientAsendsa provisionalacknowledgement(PRACK)messagethatcontainsthefinalcodecselected andClientBanswerswith200OKconfirmingthecodecselection.If183SessionProgress containedonlyonecodec,thenPRACKand200OKdonotincludeanycodecinforma- tion. At this point, both sides start to reserve needed resources for the session – for example,activatingthePDPcontext.TheIMSmayaddanauthorisationtokentothe INVITEand183SessionProgressmessages.Insuchacase,ClientsAandBmustusethe tokensinPDPcontextactivations(seeChapter3). Client A indicates a successful reservation to Client B with an UPDATE message. WhenClientBsucceedsinresourcereservation,itanswerstheUPDATEwith200OK. ClientBthenindicatestoUserBthatavideoisofferedbyUserA,andalsosendsa180 RingingmessagetoindicatetoClientAthatuserBisbeingalerted.ClientAacknowl- edgesthemessagewithaPRACK.Finally,whenUserBacceptstheoffer,ClientBsends a200OKmessageinreplytothefirstINVITEmessage.ClientAanswerswithanACK messageand startssending video. Onemaynoticethatthere aremany200OK reply messagesinthefigure.Every200OKmessagecontainsasequencenumberthatmatches thatofthemessageitreplies.Hence,thereisnopotentialconfusion. The UPDATE and PRACK messages are specified in 33 and 34, respectively. During video sharing, any of the users can pause the video stream for a period of time. The pause and resume commands are all carried inside an INVITE message thatisinturnacknowledgedbya200OKmessage. 2.2.9 VoiceoverIP(VoIP) VoIPisatechnologyusedtotransfervoiceoveranIPnetwork.VoIPdoesnotreferto anyparticularapplication,butcanbeusedindifferentscenarios.Themaindriversfor VoIParecostsavings,wirelesscoverageexpansionandrichercommunicationservices enabledbybetterprogrammability.VoIPtechnologycanbeusedoverdifferentnetworks suchasfixedbroadband(DSL/cable),WLAN(IEEE802.11)andcellular3G. VoIPtechnologyisfragmented,andthereareseveralVoIPimplementationsthatdo not interoperate properly together. One example of differences between VoIP imple- mentations isthe signallingprotocol used.IETF, 3GPP/3GPP2 standard systemsuse SIP,whileothersystemsusedifferent,non-interoperableprotocols. VoIP technology also has a place in the cellular environment. The first VoIP over cellularservicesarealreadyinuse.ThepopularPoCservicehasbeenlaunchedbyseveral operatorsaroundtheworld.With3Gnetworksandhandsets,conversationalfull-duplex VoIPservicesbecomefeasible.Thisopensupnewpossibilitiesforrichcommunication services. 3GPP networks will be able to offer an adequate level of quality for VoIP services35.3Genhancements,suchashigh-speeduplinkpacketaccess(HSUPA)and high-speed downlink packet access (HSDPA), will further increase cellular networks’ capabilitiestoproviderichcommunicationservices.MobileServiceApplicationsandPerformanceinUMTS 25 VoIPisnotmandatoryforconversational-richcommunication–thatis,RichCall– servicesinacellularnetworkenvironment.OnealternativeistofirstcombineCSvoice withanIPdatasession.DeviceswillberesponsibleforlaunchingandmanagingRich Callsessions,suchasinstantmessaging,documentsharingorrealtimeVS.Eventhough RichCallservicesuseaCSbearerinthecellulardomain,theservicesarenottiedtoit,but runoveranybearersupportingIPsuchasWLAN. VoIPservicesetupincellularmaybesimilartotheonepresentedforVSinSection 2.2.8,incasethesessionsetupusesSIP. 2.2.10 Presence The ability and willingness to be reached for communication is defined by items of informationknownas‘presenceinformation’36.Presenceinformationmayberelated tothemobilenetworkconnectionstatus;however,itrepresentsmuchmore thanjust end-usernetworkcoverage.Withpresenceitispossibletodefineasetofaccessrulesto controlaccesstopresenceinformation.Auser’sprofilemaybeeitherpubliclyvisibleor visibleforarestrictedgroupofusers.Someexamplesoftheinformationthatcouldbe storedintheprofilearelistedbelow: . Personalstatusorphoneprofile(available,busy,onholiday,inameeting). . Terminalstatusandcapabilities(status:switchedoff,outofcoverage,engagedina videoconference;capabilities:supportschatandinstantmessaging). . Location,whichdoesnotnecessarilyrefertothegeographicallocation(intheoffice,at home,on-the-move). . Otherinformation(name,address,telephonenumber,emailaddress,logo). . Mood(happy,frustrated,angry,sad). . Listofgamestheusercanplay(he/shehasdownloadedand/orhasgeneralinterestin playingit). Bysupportingapresenceserviceinthenetwork,theoperatorhasthecapabilitytooffer anexcitingrangeofadvancedpresence-basedservicesandapplications.Forinstance, presence information may be used by such applications as online gaming. Instead of blindlyloggingontoagamesmasterserver,itwouldbepossibletoseewhoisplayingand invite other users to join a game. A user simply has to subscribe to the presence information of friends. This presence information can be displayed in a list format showing who is playing, who is online and available, and who is not. Third-party callcontrolcouldevenautomaticallyinitiateagamingsessionwheneverybodyisready. SIP presence is defined as ‘subscription to and notification of changes in the com- municationsstateofauser’.Presenceholdsthemeansofcommunicationinwhichthe usercanbereached–thatis,instantmessaging(IM),call,email–oritcanprovideother information of the user: home page, picture, announcement text, mood, etc. In SIP presence,UserAisabletosubscribe(usingSUBSCRIBEmethod)tothestatusofUserB andbenotified(usingNOTIFYmethod)whenthereisachangeinUserB’sstatus. www.allitebooks.com26 QoSandQoEManagementinUMTSCellularSystems 2.2.11 Instantmessaging(IM) IMisdefinedastheexchangeofcontentbetweenasetofparticipantsinrealtime.IM typicallydiffersfrom,forexample,emailinthatinstantmessagesareusuallygrouped togetherintobriefliveconversations,consistingofnumeroussmallmessagessentback andforth.Thereareseveraldifferentmessagingschemes: . First,thereisthedistinctionbetweenone-shotmessagingandconversationalmessa- ging.One-shotmessagingmeansthatthereareonlyafew(usually1–2)messages, whichareexchangedbetweenclients.IMandmultimediamessagingusuallybelongto thiscategory. . Anothermessagingschemeissession-basedmessaginginaseparateSIPsession,which isestablishedusingSIPINVITEinastandardway.Actualmessagesmaybecarried inside the session using, for example, the RTP text, TCP-pipe or SIP MESSAGE method. So,theMMSdescribedinSection2.2.2mayalsobeprovidedusingIMSandSIP.3GPP R6defineseventighterintegrationoftheMMSwiththeIMSespeciallyforaddressing andusingSIPasawaytonotifytheUEoftheMMSreceived8. 2.3 PS service performance in UMTS End-user requirements on wireless packet data connections are simple – it should be possibletosetupconnectionsquickly,providehighandstablebitratesforinstantservice delivery on the move, and the price should be affordable. Finding the right cost/per- formancetrade-offrequiresvendorandoperatorunderstandingofthecompleteend-to- endchain.Thisincludesaspectssuchasapplicationdesign,applicationrequirements, networkfeaturesaffectingtheapplicationperformanceandhowtodeliverasufficient end-user experienceinanationwidenetworkwithmultiple services. Figure 2.9shows differentaspectsinend-userexperiencedelivery. QoE is a function of multiple protocol layers and network elements. The radio interface is typically the bottleneck, with its restrictions in bandwidth and coverage. LookingatWCDMAandenhanceddataratesforGSMevolution(EDGE)networks with applications in mind provides a number of insights that reveal possibilities and challenges. One key finding is that both WCDMA and EDGE already enable many servicestoday.ThestrongtechnologyevolutioninWCDMAandEDGEoverthepast coupleofyearsdecreasesthedifferencebetweenfixedandwirelessnetworksandhence furthersimplifiesservicedeliveryinthewirelessdomain. Ontheonehand,therearemanyservicesanditisnotpossibletohandleeachservice independentlyintermsofplanning,monitoring,etc.Ontheotherhand,serviceshave differentdelayandbitraterequirements.Byexploitingthefactthatrequirementsare different, network capacity may be increased. A reasonable solution is therefore to provideanumberof‘bit-pipes’whereeachbit-pipehostsmultipleserviceswithsimilar QoSrequirementsandwherethenetworkprioritisesthesebit-pipesdifferently.MobileServiceApplicationsandPerformanceinUMTS 27 Application How to efficiently How do applications work in deliver the services in a performance the network at light load? network with significant Are new network features load without an needed? When is the end- overdimensioned user satisfied with the network? service? End-user experience Dimensioning, Network quality of service performance monitoring and capacity and service management Does the network perform as expected when Doesthenetworkperformasexpectedwhen tthe he ooriginal riginal ddimensio imensioning ning is wadone? s doneIs ? it Is it possibletodifferentiatemonitoringby possible to differentiate monitoring by services?Arethecriteriasetforend-user services? Are the criteria set for the end-user experiencemet? experience met? Figure 2.9 ThreeaspectsofdeliveringsufficientQoEina(wireless)datanetwork. In this section we look at the end-to-end chain by first considering the general application performance aspects and key performance indicators (KPIs) of content- to-personandperson-to-personapplications.Then,wedescribehowapplicationsbehave in WCDMA, EDGE and in multiradio environments. In the WCDMA and EDGE contextbothcommercialnetworksandimprovementstiedtothetechnologyevolution arecovered.MoreinformationonaccessnetworkperformanceisprovidedinChapter5. 2.3.1 Generalapplicationperformance ThissectionbrieflyintroducessomeQoEaspectsforvarious serviceapplicationsand describeshowtheyrelatetobothservicefunctionalcharacteristicsandmobilenetwork performance. 2.3.1.1 Content-to-person applications: bit rates and round trip time Formanycontent-to-personapplications–forinstance,webbrowsingandfiledown- loading–theKPIisthetimefromthemomenttheuserclicksakeyuntiltheservice (webpage)isdelivered.DownloadtimesforatypicalInternetwebpageandMP3fileare giveninTable2.1.Thenumbersassumethatthestatedapplicationlevelbitratesare reacheddirectlywhentheuserclicksthekey. Becausewebbrowsingisverymuchaninteractiveservice,thetotaldownloadtimeofa webpageshouldbelowerthan4–10s.Theacceptableleveldependsoniftheclick-to- contenttimereferstothetimewhenthefirstpartsofthewebpageareshown(text),orthe totalpage(textandpictures).The4-srequirementisfulfilledforEDGEandWCDMAin Table2.1.DownloadinganMP3songislessinteractiveanditisexpectedthattheuseris satisfiedwiththedownloadtimeifitisacoupleofminutes.Thisisalsofulfilledwith EDGEandWCDMA.28 QoSandQoEManagementinUMTSCellularSystems Table 2.1 ThehigherbitratesinEDGEandWCDMAyieldlowclick-to-contenttimesfor applicationswithlargedataamountsaswell. Application 40kb/s 200kb/s 384kb/s 2Mb/s (GPRS) (EDGE) (WCDMA) (WCDMA/HSDPA) Laptopbrowsing 40s 8s 4s 1s (200kBpage) 0 0 0 MP3songdownload(4MB) 13 2.6 1.3 20s Other content-to-person applications such as audio and video streaming are in addition to the click-to-content times characterised bythe bit rate during the service. Videostreamingtoamobilestationwithalimitedscreensizerequiresconstant/stablebit rateshigherorequalto64kb/sforgoodqualitywithcurrentcodecs.Withcodecsbased onthecurrentavailable3GPPspecifications,thestreamingqualityisfurtherimproved formobilestationbasedstreamingupto128to384kb/s. Acommonfunctioninstreamingapplicationsisadaptationofthecontentbitrate.Itis neededbecauseend-userexperienceforstreamingdependsalotonthebitrate,which variesinandbetweennetworks. Whattheend-usersexperienceistheaverageapplicationlevelbitrate,whichisoften lowerthanthemaximumbitrateprovidedbytheradiotechnology.Oneexplanationfor thisisthatinbrowsing,HTTPandTCPresideinbetweentheapplicationandtheradio protocols. Theso-calledpacketroundtriptime(RTT)isonefundamentalpropertythataffects theefficiencyofHTTPandTCP.Itisthetimeittakestosendasmallpacketfroma computertoaserverandbackagain.IfthepacketRTTislarge,ittakesalongtime beforethereisaresponsebackfromtheserver.ThepacketRTTdetermineshowfast TCPcanestablishaconnectionand,insomecases,alsothemaximumsustainablebit rate.Theend-usercanhenceexperiencethenetworkasslowevenifthenetworkoffers highradiobitrates. Asenderandareceivermustcontinuouslycontrolthetransmissionratewhenexchan- ging data. This is in order not to congest the network when multiple users share the resources,butalsoinordernottosenddatafasterthanthebandwidthofthenarrowest linkinthetransmissionpath.Tocopewiththis,TCPgoesthroughtheadaptationstates illustratedinFigure2.10anddescribedbelow: . Synchronisation.Inthisphasethesenderandreceivernegotiate,forexample,thesizes ofthesenderandreceiverbuffers. . Slow-start. The sender gradually increases the transmission rate when it receives acknowledgementsfromthereceiver. . Steady state.Thesendertransmitsnewpacketsassoonasithasreceivedacknowl- edgementsfromthereceiverthatthereceiverisreadytoacceptmorepackets. A short RTT speeds up the synchronisation and the slow-start because of the faster informationexchange.DuringthesteadystatetheRTTdoesnotaffecttheperformance

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