User-Perceived Quality of Service in Hybrid Broadcast and Telecommunication Networks

Transcription

1 Usr-Prcivd Quality of Srvic in Hybrid Broadcast and Tlcommunication Ntworks Michal Galtzka Fraunhofr Institut for Intgratd Circuits Branch Lab Dsign Automation, Drsdn, Grmany Abstract In this papr, basic idas for modling usr-prcivd quality of srvic in hybrid ntworks will b prsntd. Th charactristics of th diffrnt parts of ths ntworks hav to b considrd, taking into account that srvics in hybrid ntworks will b mor than an nd-to-nd data transmission. Rathr, ths srvics will us for xampl local or cooprativ caching mchanisms. Thrfor, th rlationship and dlimitation of broadcast, multicast, and unicast data transmission has to b discussd in this contxt. Thus, modling dos not only includ pur ntwork charactristics lik data rat and rror probability, but also paramtrs lik application structur and charactristics, charactristics of th actual trminal quipmnt, usr profils, and information about currnt location or motion of th usr. Kywords Usr-prcivd Quality of Srvic, Modling, Hybrid ntworks INTRODUCTION Ubiquitous Computing, 4G Mobil or TV anywhr ar buzzwords dscribing similar convrging trnds from th prspctiv of diffrnt rsarch filds: In th futur, vryon is xpctd to b abl to rciv and xchang information rgardlss of his location and situation. For a usr it has to b transparnt which communication tchnology a ddicatd srvic is basd on. On th othr hand, th providr of th srvic or srvic packag who again will us (and pay for) srvics of diffrnt ntwork providrs must b abl to plan, configur, and optimiz th utilization of th undrlying hybrid ntwork according to th rquirmnts of his customrs and dpnding on th availabl ntwork rsourcs. Against this background, thr is a nd for th srvic providr as wll as for th nd-usr s bnfit to mak th (usr-prcivd) quality of srvic (QoS) somhow calculabl. Traditionally, QoS is a trm applid in tlcommunication ntworks. With th upcoming of multimdia straming srvics in th Intrnt, issus rsulting from th original bst ffort policy hav to b handld hr, too. Rlating QoS concpts in th Intrnt ar focusd on a packt-basd nd-to-nd communication. Typical QoS paramtrs lik dlay and loss rfr to this packt transport at diffrnt layrs. Altrnativly, thr is a common hop, that th continuously incrasing bandwidth in th Intrnt will ovrcom ths bottlncks. This might hav bn tru in th past particularly for th cor ntwork. Anyway, thr will b QoS rlvant tchnological challngs in th convrging nxt-gnration ntworks causd by a varity of accss ntworks. In particular, wirlss (including broadcast) ntworks will b intgratd thr for th distribution of multicast contnt. Evn if dlay and loss or mor gnral at th usr lvl, paramtrs lik accss tim, timlinss, availability, or corrctnss ar important QoS paramtrs from th usr's point of viw, too, thr is no simpl way to map QoS paramtrs btwn diffrnt ntwork and usr lvls. Starting with dfinitions of th rlvant trms, th basic modling approach will b discussd. Th rlationship btwn tchnical constraints and th usr-prcivd quality of srvic will b illustratd with an xampl of data srvics in digital TV. Extnding this approach to data srvics which us hybrid broadcast and tlcommunication ntworks, common QoS concpts at svral ntwork layrs hav to b takn into considration. HYBRID NETWORKS Nxt gnration ntworks ar discussd from a varity of viws. Rgardlss whthr th focus is on broadband fibroptic or satllit cor ntworks, th us of wirlss ad-hoc ntworks or th intgration of broadcast ntworks, thr ar som common charactristics (among othrs) [10]: coopration of diffrnt ntworks samlssnss, srvic continuity vrtical and horizontal roaming all-ip sparat srvic providrs (srvic, ntwork, contnt) Broadcast ntworks ar intrsting in ths scnarios not only bcaus of th high bandwidth at a rlativly high mobility, but also bcaus of thir spcific charactristics rlating to straming and multicast. On th othr hand, th lack of rturn channl functionality in broadcast ntworks limits th possibilitis of intractiv applications in pur broadcast ntworks to a simpl local intraction. In this contxt, th trm hybrid ntworks dscribs scnarios of convrging ntworks with broadcast ntworks (mainly for th distribution of multimdia contnt and/or othr multicast contnt) and communication ntworks (stationary, portabl, or mobil for th intraction and th uni- 39

2 cast contnt). Svral projcts ar daling with this subjct. [3]. Srvic Providr Mobil / portabl Srvic DVB-T DVB-S DAB Broadcast channl trms in a broadr contxt ar: Application lvl QoS, Quality of Exprinc (QoE), Quality of Businss (QoB), Quality of Contxt (QoC) tc. [13], [11], [2] In [8], a framwork for communications QoS is dfind. As shown in Figur 2, this rvals an obvious difficulty: Probably, th srvic providr is abl to dfin and masur th QoS paramtrs basd on th QoS paramtrs of th ntwork(s) usd. Hwvr, ths tchnical paramtrs hav to b mappd to th usr prcivd catgoris of QoS which itslf focus on crtain usr-prcivd ffcts rathr than on thir causs within th ntwork. Intrnt Intraction channl GSM GPRS UMTS BT WLAN Figur 1. Scnario for hybrid ntworks Trminals Customr Customr s QoS Rquirmnts Srvic Providr QoS Offrd by Providr In fact, w hav to discuss th qustion whthr multicast is limitd to isochronous data transmission only which is a particular advantag of using broadcast ntworks within such scnarios. Rathr, th xploitation of local or vn cooprativ caching mchanisms [4] may xtnd th usability of multicast from a strict isochronous transmission to a wakr intrprtation of ral-tim data provision making broadcast ntworks usabl for a broadr rang of data srvics. SERVICES AND QUALITY OF SERVICE Srvics In th fild of tlcommunications, a srvic is dfind as th ability of a ntwork to transmit ddicatd information [12]. Historically, thr is a clos association btwn srvic, srvic providr and th ntwork. Morovr, w also know IT-srvics, databas srvics, or ntwork srvics. Economically, a srvic is th non-matrial quivalnt of a good. Evn if w focus hr on ntworks and hnc our srvics ar data srvics in som rspct, w hav to considr a srvic as indpndnt of a ddicatd ntwork tchnology as much as possibl. For xampl, it could b imaginabl that on srvic packag soccr information covring applications lik TV transmissions, onlin tickr, SMS or MMS srvic, radio broadcast tc. would b offrd instad of singl, sparat srvics of diffrnt srvic providrs in diffrnt ntworks and paid for sparatly by th usr. On th othr hand, such a srvic of cours is tchnically not indpndnt of th undrlying ntworks. Espcially, th quality of this srvic th usr is prciving is influncd by th quality of data transmission ovr th ntwork(s). Quality of Srvic A lot of diffrnt dfinitions and paramtrs for quality of srvic can b found. In [7], QoS is dscribd as th collctiv ffct of srvic prformanc which dtrmins th dgr of satisfaction of a usr of th srvic. Rlatd End-usr multimdia QoS catgoris ar charactrizd in [9]. Thr ky paramtrs of QoS impacting th usr ar idntifid thr: dlay QoS Prcivd by Customr Figur 2. Th four viwpoints of QoS [8] dlay variation QoS Achivd by Providr information loss Basd on ths ky paramtrs svral groups of applications and thir dpndncis on ths paramtrs ar idntifid. For xampl, a straming vido application is snsitiv to dlay variation, but dlay itslf dos not affct th usr-prcivd QoS significantly. In contrast, an intractiv voic or vido application is snsitiv to both, th dlay and th dlay variation. Thr ar rlatd works and standards utilizing this framwork (.g. [1]). Dfinition of QoS Paramtrs Th mapping problm mntiond abov dos not only xist btwn customr and srvic providr. Additionally, it has to b considrd btwn srvic providr and svral ntwork providrs, too. Morovr, ach ntwork layr has its own utilization of QoS paramtrs and thrfor a mapping has to b prformd btwn ths layrs, as wll. For xampl, at IP lvl w hav to dal with dlay and loss (loss normally is assumd to b causd by congstion rathr than by transmission rrors at physical layr). At TCP lvl loss is avoidd bcaus of th rtransmission 40

3 mchanisms of th TCP protocol. Howvr, a crtain loss rat at IP lvl will rsult in an additional dlay at TCP lvl. Figur 3 shows th layrs intrsting for digital TV (DVB) transmission as usd in th xampl blow. Following th xplanations abov, w want to dfin gnral QoS paramtrs which covr th nd-usr viw, but can b xtndd to rflct ntwork layr aspcts as wll. In [14] four paramtrs ar mntiond: availability, prformanc, accuracy, and affordability. Evn though this work focuss on IT srvics, ths paramtrs may b usd for our gnral purposs, as wll. Carousl MPE or SI MPEG Tabls/Sctions MPEG-TS PHY (MOD, FEC, ) Cycl Tim, Organization Channl Dlay, Bit Errors Application Dcapsulation MPEG Tabls/Sctions MPEG-TS PHY (DEMOD, FEC, Figur 3. Paramtrs across transport layrs affcting QoS Availability This trm dos not only dfin whthr a crtain srvic is availabl or not. It also may includ statmnts about th compltnss of th data for a crtain srvic or application. Timlinss W us "timlinss" as th usr prcivd quality paramtr of prformanc. This paramtr givs us th masur whthr th usr s rqusts for data ar satisfid in an appropriat tim. Accuracy This trm gnrally tlls us whthr th data prsntd to th usr ar corrct. Accuracy may b affctd.g. by data corruption during transmission as wll as by out-datd cach data. Affordability This rprsnts th costs ncssary to achiv a crtain dgr of th othr QoS paramtrs availability, timlinss, and accuracy. Ths dfinitions of QoS paramtrs rflct th usr s viw of th srvic. Th actual intrprtation is spcific to a crtain srvic as wll as th mapping to th rlatd QoS paramtrs of th undrlying ntwork(s). MODELING USER PERCEIVED QoS If w want to quantify th QoS paramtrs dfind abov, w nd a modl which covrs all aspcts of our srvic. This starts with spcific charactristics of th srvic rprsntd by a crtain application running on on or mor kinds of trminals with diffrnt faturs. Ths trminals may b usd by on or svral prson(s) with diffrnt nds and prfrncs. Th prsons may mov and hnc thr location has to b considrd in th modl. Dpnding on thir location, thy may b facd with diffrnt rcption conditions of th ntworks supportd by a crtain srvic and/or trminal and so aftr all, th ntwork QoS of th participating ntworks is (only) on of th paramtrs to b considrd in our modl. Figur 4 givs an ovrviw of ths dpndncis. W can dfin a st of u us cass dscribing in which way a usr utilizs this srvic. For th vctor Q of usrprcivd QoS paramtrs Q f, W Q0, Q u th function f W might b som kind of srvic spcific wight function for th QoS paramtrs of all us cass. Srvic charactristics structur softwar scaling caching Trminal quipmnt softwar storag availabl ntwork intrfacs powr consumption Ntwork charactristics (of all potntially includd ntworks) data rat dlay bit rror rat costs QoS componnts Availability Timlinss Accuracy Affordability Location information usr location motion prdiction availabl ntworks rlvanc of srvic Usr profil srvic lvl prfrncs... Figur 4. Paramtr dpndncis for QoS modling 41

4 For ach us cas th QoS paramtrs hav to b dtrmind from th modl. This is again srvic spcific, and that s why w will dmonstrat it by an xampl. Exampl As an xampl, w want to invstigat a srvic which might b rgardd as a ky application in digital TV an Elctronic Program Guid (EPG) [6]. An EPG can b usd as an advancd navigation tool through th grat varity of TV programs. It assists in zapping through th channls as wll as finding spcial vnts at a crtain tim. Th EPG application uss program data providd by th TV broadcastrs, and hnc it is a data srvic as dfind abov. EPG data may b transmittd within Evnt Information Tabls (EIT) as part of th so-calld DVB Srvic Information (SI) [5], or thy may b providd by a srvic providr within a sparat data stram. In both cass, data hav to b transmittd continuously in a data carousl bcaus of th broadcast natur of th data channl. For xampl, th functional rquirmnts ar: Gtting a quick ovrviw of a all currntly running vnts and of th vnts starting immdiatly aftr thm (s Figur 5). Gtting an ovrviw of vnts running at a crtain tim in th nar futur (within svral days). Prsnting xtndd information for slctd vnts. Additional rquirmnts rgarding th usr-prcivd quality ar: Th EPG should always prsnt th up-to-dat vnt information, vn if th schdul changs. Th usr should b abl to accss th EPG data within an appropriat tim (dpnding on th functional rquirmnts abov. Figur 5. Now & nxt viw of an EPG Figur 6 shows a us cas diagram for such an EPG srvic including QoS rquirmnts. For th spcific QoS paramtrs w dfin th man accss tim t A (timlinss), th dgr of compltnss C (availability) and th dgr of up-to-datnss A (accuracy). Th affordability will not b dalt with in this xampl. In th following w want to concntrat on us cas Ovrviw at tim t (which in fact is a gnralization of us cas Ovrviw Now & Nxt, but with diffrnt QoS rquirmnts) with short and xtndd vnt information. W suppos an implmntation (s Figur 7) which optionally uss a caching mchanism to avoid long man accss tims to th carousl. For simplification, w furthr assum hr a singl privat EPG data stram rathr than using th EIT on svral transport strams. Additionally, th figur shows a rturn channl which could srv as a opportunity to accss supplmntary ud Elctronic Program Guid Elctronic Program Guid Ovrviw Now & Nxt «includ» Show Short Information of ach vnt {Min. Compltnss: 1.0 (currnt day), 0.8 (nxt day), 0.6 (othr days) Min. Up-to-dat: 1.0 (currnt day), 0.9 (nxt day), 0.8 (othr days)} {ta <= 3 s} «includ» «xtnd» {ta <= 5 s (currnt day), 10 s (othr days) TV usr Ovrviw at tim t «includ» Show Extndd Information for on vnt Min. Compltnss 1.0 (currnt day), 0.8 (nxt day), 0.6 (othr days) Min. Up-to-dat: 1.0 (currnt day), 0.9 (nxt day), 0.8 (othr days)} {ta <= 10 s} «xtnd» {ta <= 15 s Sarch for Gnr {ta <= 10 s} ta: man accss tim Show picturs, v ido clips, associatd information,... Min. Compltnss: 0.6 (currnt day), 0.4 (nxt day), 0.2 (othr days) Min. Up-to-dat: 1.0 (currnt day), 0.9 (nxt day), 0.8 (othr days)} Figur 6. Us cas diagram for Elctronic Program Guid 42

5 EPG data,.g. picturs, vido clips. Th lattr cas will not b discussd in dtail hr. Data sourc Data carousl W prsum an avrag numbr of vnts pr day pr channl of Day = 25. Thr ar EPG data availabl for p max = 100 channls on 8 days with a data rat of r C = 1 MBit/s. Data ar snt in on fil pr day. Lt E S = 100 b th avrag siz of short vnt information (in byt) and E E = 300 th avrag siz of xtndd vnt information. Timlinss: For th cycl tim t c of th data carousl w gt E E r s tc 8 Day pmax S E C 64 sd Ovrviw at tim t t A :TV usr Data Carousl Intrnt Gt EPG Now_Nxt Data t D Show EPG Now_Nxt Data Show EPG Now_Nxt Data (rrornous) Cach Modm EPG Frontnd EPG Frontnd Figur 7. Functional implmntation of an EPG srvic EIT Data {dlay} Listn to sourc EIT Data {dlay} Listn to Sourc again EIT Data {dlay} Data Carousl Data Sourc Figur 8. Squnc diagram for EPG us cas Ovrviw at tim t t C Usr Thrfor, th download tim for on data fil is t D = 8s. As w can s in Figur 8, th actual accss tim is not dpndnt on any dlay on th channl. It rathr dpnds on th cycl tim t c of th carousl, th download tim t D and som procssing tim, which shall b nglctd hr. If w assum, that th usr rqusts occur uniformly distributd within th cycl tim intrval, for th avrag accss tim t A applis: t A 0.5 tc t D 40s If th data transmission is rronous, th download tim will incras by on cycl t c. Supposing a bit rror rat of lowr than for a satllit channl, t A would incras only by about 5ms. Howvr, for a trrstrial channl and mobil rcption, w would hav to considr a location dpndnt bit rror rat, which is xpctd to hav a strongr influnc on th QoS. Availability, Accuracy: Assuming that th data sourc is complt and corrct, both valus would b 1. Cach Timlinss: W only hav to considr a constant procssing tim which can b nglctd hr. Availability: Abov w dfind compltnss C as th spcific paramtr for availability within th EPG srvic. It dpnds on th cach siz and th caching stratgy. W prsum that vnts will b cachd with short and xtndd information until half of th cach is filld, bginning with th arlist vnts. Aftr that, only short information will b stord until maximum cach siz is rachd. If w normaliz tim to th avrag numbr of vnts pr day, w gt an vnt tim t. t = 0 dnots th tim of th currntly running vnt, t = 1 th following and so on. t,full shall b th vnt tim of th latst vnt stord with both th short and th xtndd information, t,max accordingly dnots th vnt tim of th latst vnt stord in th cach at all. Lt b n c = 1 MByt th maximum cach siz and p = 50 0 p p max th numbr of TV programs configurd for th EPG. Thn for t,full and t,max applis: 0.5 nc t, full 26 (which is about 1 day) and p ES EE 0.5 nc p t, full ES t, max 130 (about 5 days). p ES Thn w gt for th compltnss at vnt tim t : 1 0 t t,max C S t for short information only 0 t t,max and for short and xtndd information 1 0 t t, full CE t 0 t t, full Accuracy: W assum that th cach will b filld at a suitabl tim t = -t u bfor currnt tim t = 0. Additionally w suppos that w know a distribution function a U (t) for th probability that on vnt information will b changd ditorially in th data stram at a crtain tim t. Furthrmor, lt th distribution function a E (t) dscrib th probability that at a crtain tim t an originally plannd TV vnt is out-datd bcaus of som currnt incidnt. Both distributions ar implid to b indpndnt. Thn, for th probability that thr ar no out-datd vnts in our EPG 43

6 srvic btwn now t = 0 and a crtain tim t thr applis: A Cach t t 1 a t dt a t U tu t 0 EPG front-nd Finally, w hav to comput th QoS paramtrs which dirctly influnc th usr s prcption. Within th EPG front-nd in our xampl th implmntation of th EPG srvic controls whthr a usr rqust has to b forwardd to th cach or must b fulfilld by obtaining data dirctly from th carousl. Timlinss: Th man accss tim now dpnds on th vnt tim t and can b xprssd as t A t t t A, Cach 0 A, Carousl E t t t t,max dt,max Availability: Bcaus of th possibility to obtain data from th carousl, th compltnss C(t ) of data should always b 1 (prsumd that th rspctiv vnt information is providd at all). Accuracy: If w obtain data from th cach w cannot chck if ths data ar up-to-dat rally. Thrfor, for accuracy A(t ) applis: A t A Cach 1 t 0 t t t t,max,max Th usag of a rturn channl as mntiond in Figur 7 (.g. for acquiring additional EPG data lik photos, vido clips tc.) would contribut furthr paramtrs rlvant for th ovrall usr-prcivd QoS (.g. data rat of th modm, stup tim of a connction). SUMMARY AND OUTLOOK Th rlativly simpl xampl discussd abov dmonstrats a numbr of problms which hav to b considrd whn modling usr-prcivd quality of srvic in hybrid ntworks. Starting from a dtaild undrstanding and modling of th application ralizing a crtain srvic, ach of th gnral QoS paramtrs has to b dfind and dscribd carfully. According to Figur 4, a varity of paramtrs may hav influnc to our modl. Many of thm nd to b dscribd as probabilistic modls. Rcalling th soccr information srvic packag xampl in this papr, w nd to modl usr s habits with distribution functions for thir location (.g. on Saturday aftrnoon) as wll as th availabl ntworks and thir quality at ths locations. A hirarchical modling mthodology may vn mak us of xisting mthods for ntwork planning, modling of ntwork QoS tc. Quantifying th paramtrs for usr-prcivd QoS will b ssntial for planning and oprating srvics on futur complx ntwork structurs with srvic lvl agrmnts to guarant a crtain lvl of QoS for th usrs on th on hand, and to calculat th ncssary rsourcs and th corrsponding cost for th srvic providr on th othr hand. REFERENCES [1] 3GPP TS : Quality of Srvic (QoS) concpt and architctur v rd Gnration Partnrship Projct, 2003 [2] BUCHHOLZ, T.; KÜPPER, A.; SCHIFFERS, M.: Quality of Contxt: What It Is And Why W Nd It. In: HP OpnViw Univrsity Association 10th Workshop, Gnva, Switzrland, 2003 [3] CISMUNDUS: Fild Tst Rsults and Dmonstration. CISMUNDUS IST Projct Dlivrabl 9, [4] CAO, G.; YIN, L.; DAS,C.R.:Cooprativ Cach- Basd Data Accss in Ad Hoc Ntworks. In: IEEE Computr 2 (2004) pp [5] EN : Spcification for Srvic Information (SI) in DVB systms - ETSI Europan Standard EN V Europan Tlcommunication Standards Institut (ETSI), [6] GALETZKA, M.; LUX, S.: Elktronisch Programmführr in tchnischr Übrblick (in Vorbritung). In: Frnsh- und Kinotchnik 8/9 (2004) [7] ITU-T E.800: Trms and dfinitions rlatd to quality of srvic and ntwork prformanc including dpndability ITU-T Rcommndation E.800. Intrnational Tlcommunication Union, 1994 [8] ITU-T G.1000: Communications quality of srvic: A framwork and dfinitions ITU-T Rcommndation G Intrnational Tlcommunication Union, 2001 [9] ITU-T G.1010: End-usr multimdia QoS catgoris ITU-T Rcommndation G Intrnational Tlcommunication Union, 2001 [10] ITU: Broadband Mobil Communications Towards A Convrgd World. In: ITU/MIC Workshop on Shaping th Futur Mobil Information Socity, Soul, 2004 [11] MOORSEL,A. V.: Mtrics for th Intrnt Ag: Quality of Exprinc and Quality of Businss. In: Fifth Intrnational Workshop on Prformability Modling of Computr and Communication Systms, Erlangn, 2001, pp [12] SIEGMUND, G.: Tchnik dr Ntz. Hüthig Vrlag, Hidlbrg, [13] SILLER, M.; WOODS, J.: Improving Quality of Exprinc for Multimdia Srvics by QoS Arbitration on a QoE Framwork. In: IEEE Packt Vido, Nants, 2003 [14] STURM,R.C.:Managing Quality of Srvic. InfoVista Whit Papr,