Quality of Experience of mobile services - Telfor

14th Telecommunications forum TELFOR 2006 Serbia, Belgrade, November 21-23, 2006Quality of Experienceof mobile servicesPjer M. Vuckovic and Nevena S. Stefanovic, Telenor, SerbiaAbstract — Recent changes in mobile and wirelesstechnologies as well as the transition from voice only tocombined voice and data networks significantly affectedmobile operators. With competitive forces stronger than everit is necessary to assure high quality services in order toincrease customer retention and decrease churn. QoEconcept was developed as very efficient method of trackingcustomers’ perception of the network and its performance.Key words — QoE (Quality of Experience), QoS (Qualityof Service), UMTS (Universal Mobile TelecommunicationsSystem).AI. INTRODUCTIONccording to available research results, around 82% ofcustomer defections are due to frustration over theproduct or service and the inability of theprovider/operator to deal with this effectively. On average,one frustrated customer will tell 13 other people abouthis/her bad experiences. Also, surveys have shown that forevery person who calls with a problem, there are 29 otherswho will never call. Around 90% of customers will notcomplain before defecting – they will simply leave oncethey become unsatisfied [1].There are many reasons why mobile operator can’tafford to wait for customers to complain and then try tosolve the problem. It is necessary to find a reliablemechanism to track user experience in totality all the timeand to improve it when needed. Well known methods aresometimes simply not good enough.The purpose of this paper is to address Quality ofExperience (QoE) in mobile radio networks and to providesome bases for future work and research activities.The rest of the paper is organised as follows: in Section2 QoS concept and some new demands of future mobilesystems are presented; the main ideas behind QoE aresummarised in Section 3; the differences between QoEand QoS are given Section 4; possibilities for measuringQoE are explained in Section 5; finally, conclusions aremade in section 6.II. QUALITY OF SERVICE -QOSQuality of Service (QoS) was defined in ITU-TRecommendation E.800 as: "The collective effect ofservice performance which determines the degree ofsatisfaction of a user of the service" or simplified: thequality of service of a system describes its ability toprovide the desired quality (e.g. image or speech quality)of a given service at a given time at the “price” (money,energy or time) that the user is willing to pay.In future mobile systems the demand for QoS willincrease and at the same time the number of users andapplications will increase dramatically. In addition, thereis a need for finding a relevant way of measuring QoS,probably through a combination of objective andsubjective measurements. In other words QoS includesdynamic configuration of hardware, network and softwareplatforms for a given application in a given context inorder to optimize the use of different resources such asenergy and bandwidth.An important feature of Universal MobileTelecommunications System (UMTS) is that informationgenerated by independent sources can be efficientlymultiplexed on the same transmission medium. UMTSsupports traffic with very different bandwidth and QoSrequirements. Traffic generated by data transfer servicesand Internet access is essentially “bursty” andunpredictable. Although data transmission betweenmachines is loss sensitive, it is usually not sensitive toend-to-end delay or jitter. On the other hand, speech (andmore generally, real-time applications) requires strictlimits on the transmission delay, but can cope withreasonable loss rates [2].In order to meet new requirements, Third GenerationPartnership Project (3GPP) has defined four QoS classes:conversational, streaming, interactive, and background [3].The main distinguishing factor among these classes isdelay sensitivity. Each UMTS QoS class can be describedusing the QoS attributes that have certain ranges. Thedefined UMTS QoS attributes can be classified into threegroups: delay attributes (such as transfer delay), bandwidth attributes (such as maximum bit rateand guaranteed bit rate) and reliability attributes (such as delivery order,traffic handling priority, allocation/retentionpriority, etc) [4].Pjer Vuckovic, pjer.vuckovic@telenor.co.yuNevena Stefanovic, nevena.sefanovic@telenor.co.yuTelenor d.o.o. Bulevar umetnosti 16a, Beograd, Srbija206

TABLE 1: UMTS TRAFFIC CLASSES.QoS ClassTransferdelayrequirementTransferdelayvariationLow biterrorrateGuaranteedbitrateExampleConversational Stringent Stringent No YesStreaming Constrained Constrained No YesInteractive Looser No Yes NoBackground No No Yes NoVoIP, Video Conferencing, AudioconferencingBroadcast services (audio, video),News, SportWeb browsing, Interactive Chat,Games, m-commerceE-mail, SMS, database downloads,transfer of measurementsConversational class is the most sensitive, whilebackground is the least sensitive. Conversational andstreaming classes are intended for real-time traffic. Theyboth preserve time relation (variation) betweeninformation elements of the stream, however,conversational class has more rigorous delayrequirements. Example applications are IP telephony forthe former and streaming video for the latter. For theinteractive and background classes, transfer delay is not asimportant. Instead, they both preserve the payload content.Interactive class follows a request-response pattern anddefines three priorities to differentiate between bearerqualities, while it does not provide explicit qualityguarantees. Background’s main characteristic is that thedestination does not expect the data within a certain time.Example applications are FTP or Web traffic forinteractive and download of emails for background class.Summary of the main QoS requirements and typicalservices and applications is given in Table 1.III. QUALITY OF EXPERIENCE -QOEExperiences are actively constructed and developed bypeople interacting with the environment through asubjective process.The experience of a product/service may be defined indifferent ways. However, many authors agree that itshould comprise of all elements influencing interactionbetween the user and the product/service provided [5], [6].From user’s perspective, various attributes of theproduct have importance in determining experience. Theproduct should be needed and appropriate, and its usemanageable and learnable. Some users will valueaesthetics, others effectiveness. However, all of theseaspects are value adding and hence of great importance forthe provider of the service.User of a service has predetermined and usually welldefined expectations. These expectations mainly focus onusability, ease of interaction and performance of thesystem [7]. For the user to be satisfied with the experience,expectations must be met.While interacting with the environment, peopleexperience sensations, perceptions and opinions. Thecharacteristics of these experiences determine the overallquality of experience [6].Quality of Experience is not a metric by itself. In termsof applying QoE to services provided by 2G or 3Goperator, it is a ''concept comprising all the elements of asubscriber’s perception of the network and its performanceand how they meet expectations'' [8]. Factors such as cost,reliability, availability, usability, utility and fidelity areidentified to be critical for determining QoE of mobilenetworks (Figure 1).FIGURE 1: FACTORS CRITICAL FOR DETERMENING QOE.High QoE would indicate that the user’s experiencewith the service provided is good. On the other hand, lowQoE means that user’s experience of the network is notsatisfactory.The quality as experienced by the user (QoE) is themost important measure for the operator to properlydimension its network. The key is to find a balancebetween over provisioning and low quality extremes.While over provisioning quality is costly and inefficient,low quality might have a negative effect on churn [9].Understanding users’ expectations and identifying thedrivers of users’ satisfaction are necessary for determiningeffective QoE indicators.IV. QOE VERSUS QOSTo better understand the differences between QoS and207

QoE (as well as the requirements given to the operator andthe end user) it is necessary to provide detailedexplanation of the relation between these two factors.From customer's point of view there are four aspects ofservice use: Network Access, Service Access, ServiceIntegrity and Service Retainability [10].The meaning and explanation for each of these QoSaspects is as follows. Network Access: The network indication on thedisplay of the mobile is a signal to the customerthat he can use the service of this networkoperator. Service Access: If the customer wants to use aservice, the network operator should provide himas fast as possible access to the service. Service Integrity: This describes the Quality ofService during service use. Service Retainability: Service Retainabilitydescribes the termination of services (inaccordance with or against the will of the user).QoS is intrinsically a technical concept which usuallyhas little influence on a user. It is only a subset of theoverall QoE scope. Although higher QoS network wouldin many cases result in higher QoE, fulfilling all trafficQoS parameters will not guarantee high users’ Quality ofExperience.V. MEASURING QOEQoE is not a metric by itself and it is very subjective bynature. However, devising a strategy to measure QoE asrealistically as possible is of crucial importance for serviceprovider. In fact, knowing user perceived QoE, theoperator can estimate the contribution of networkperformance to the overall level of customer satisfaction.Reliability, availability, scalability, speed, accuracy andefficiency are the main elements that define QoE and atthe same time can provide competitive advantage innowadays packet based communication networks.Experience is expressed in words rather then metrics andcan be excellent, very good, good, fair or poor [8].There are two approaches for measuring QoE: servicelevel approach (uses statistical samples) and networkmanagement system approach (uses QoS parameters).Service level approach includes identifying andweighting QoE Key Performance Indicators (KPI),weighting the key applications, devising a properstatistical sample (like geographic areas, traffic mix etc.),utilising user agents in the handsets to make the resultsmore accurate and giving an overall QoE index from KPIvalues for each separate service and service mix.Network management system approach includesidentifying the relationship between QoS KPIs and theireffect on QoE and measuring QoS KPIs in the network torate QoE of users. While network management systemapproach seams ideal for operators (even though it isvendor dependent), it is very difficult to identify theproper relationship between network QoS KPIs and userexperience (QoE). Service level approach, on the otherhand, provides the opportunity to measure QoE for anynetwork without access to operator products (such asnetwork management system). It is operator and vendorindependent, relatively inexpensive and appropriate forbenchmarking.However, in order to obtain the most accurate results,the best option is for the operator to combine bothapproaches in a complementary way [8].VI. CONCLUSIONManaging QoE in a multi service network is one of themost challenging aspects of mobile network design. Inmobile telecommunications of the future, by properlydimensioning and maintaining high QoE network,operators may gain critical competitive advantage. UMTSis the first wireless technology in which serious emphasison end-to-end QoS has been given.The purpose of this paper is to provide an overview ofQoE concept in mobile networks, to explain how QoErelates to QoS and to outline the challenges mobileoperators have today. Future work will be concentrated oncareful analysis of available services and, in the nextphase, defining exact QoE targets and possibilities formeasuring QoE for each of identified services.QoE is a new concept in mobile networks. The authorsattempted to (through synthesis of knowledge gained fromexperience, and available literature in this field) stress that,in UMTS networks, it is critical for operators to focus onboth QoS KPIs on one hand, and customers’ expectationsand perception of the service on the other in order to beable to properly dimension and manage mobile network.LITERATURE[1] Fiedler, M. “The Role of Quality Feedback for Perceived ServiceDependability”, http://iplu.vtt.fi/digitalo/dependability_espoo_060518_mf.pdf, accessed on July 25, 2006.[2] Baudet, S. et al. “QoS implementation in UMTS networks”, AlcatelTelecommunications Review, quarter 1, 2001.[3] 3GPP TS 23.107 Technical Specification Group Services andSystem Aspects; Quality of Service (QoS) concept and architecture.[4] Chuah, M.C. et al. “Design and Performance of 3GNetworks/WLANs”, Springer, Boston, MA, page 41, 2005.[5] Patrick, A. Et al. “A QoE Sensitive Architecture for AdvancedCollaborative Environments”, The first international conference onQuality of Service in heterogeneous wired/wireless networks(QSHINE 2004), October 18-20, 2006 Dallas, TX.[6] Lauralee, A. “Quality of experience: defining the criteria foreffective interaction design”, Interactions, Volume 3, Issue 3,May/June 1996.[7] Fiedler, M. “State-of-the-art with regards to user-perceived Qualityof Service and quality feedback”,http://eurongi.enst.fr/p_en_WPs_JRAWP_WPJRA6_140.html,accessed on July 25, 2006.[8] Nokia White Paper “Quality of Experience (QoE) of mobileservices: Can it be measured and improved?”,http://www.nokia.com/NOKIA_COM_1/Operators/Downloads/Nokia_Services/whitepaper_qoe_net.pdf, accessed on July 25, 2006.[9] Laiho, J. Et al. “Advanced Analysis Methods for 3G CellularNetworks”, http://www.cis.hut.fi/kimmo/papers/twc05.pdf,accessed on July 25, 2006.[10] ETSI TS 102 250 Speech Processing, Transmission and QualityAspects (STQ); QoS aspects for popular services in GSM and 3Gnetworks; Part 1: Identification of Quality of Service aspects.208

ABSTRACTRecent changes in mobile and wireless technologies aswell as the transition from voice only to combined voiceand data networks significantly affected mobile operators.With competitive forces stronger than ever it is necessaryto assure high quality services in order to increasecustomer retention and decrease churn. QoE concept wasdeveloped as very efficient method of tracking customers’perception of the network and its performance.QUALITY OF EXPERIENCE OF MOBILESERVICESP. Vuckovic, N. Stefanovic209