Master Thesis Electrical Engineering December 2012 Analysis of Radio Access Network Buffer Filling Based on Real Network Data Logabharathi Aruchamy School of Computing Blekinge Institute of Technology 37179 Karlskrona Sweden This thesis is submitted to the School of Computing at Blekinge Institute of Technology in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. The thesis is equivalent to 20 weeks of full time studies. Contact Information Author: Logabharathi Aruchamy E-mail: [email protected] External Advisor(s) Tomas Lundborg, Mathias Sintorn, Systems Manager, Senior Specialist R&D, Ericsson AB, Ericsson AB, Development Unit Radio-System and Development Unit Radio-System and Technology, Technology, Torshamnsgatan 33, Torshamnsgatan 33, 164 80 Stockholm, Sweden. 164 80 Stockholm, Sweden. University advisor: Prof. Markus Fiedler, School of Computing (COM) School of Computing Internet: www.bth.se/com Blekinge Institute of Technology Phone: +46 455 385000 371 79 KARLSKRONA SWEDEN SWEDEN Abstract The 3G and 4G networks have drastically improved availability and quality in data transmission for bandwidth hungry services such as video streaming and location-based services. As 3G networks are very widely deployed, there exists increased capacity requirement and transport channel allocation to simultaneous users under a particular cell. Due to this reason, adequate resources are not available, which in turn degrades both service quality and user experienced quality. This research aims at understanding the characteristics of buffer filling during dedicated channel (DCH) transmission under fixed bit-rate assumptions on a per-user level taking different services into consideration. Furthermore, the resource utilisation in terms of empty buffer durations and user throughput achieved during dedicated channel transmission are also analysed for different data services existing in the mobile networks. The traces are collected from a real network and characteristics of the traffic are analysed prior to understanding its buffer filling in Radio Network Controller (RNC) during downlink data transmission. Furthermore, the buffer is modelled with some series of assumptions on channel bit-rates and simulations are performed taking single user scenario into consideration, for different services with the help of obtained traces as input to the buffer. This research is helpful in understanding the RNC buffer filling for different services, in turn yielding possible understanding on the existing transport channel switching scenario. With the help of analysing the buffer filling for different services and transport channel utilisation, we learn that most of the data services show low DCH utilisation of approximately around 20% and also found to have 80% of the total DCH session duration with empty buffer, causing sub-optimal radio resource utilisation. Keywords: Traffic Characteristics, Radio Network Controller (RNC), Dedicated Channel (DCH) and Channel Switching. i Acknowledgement It would not have been possible to complete my thesis work without the help and support of the kind people around me, to only some of whom it is possible to give particular mention here. Foremost, I would like to express my deepest sense of Gratitude to Jessica Ostergaard,¨ Manager, Radio Networks - Systems and Concepts, Ericsson AB, for giving me such an wonderful opportunity to perform this thesis work at Ericsson AB. At this moment of accomplishment, I gratefully acknowledge Tomas Lundborg, Systems Manager for his continuous advice and encouragement throughout the course of this thesis. I thank him for his systematic guidance and great effort he put into training me in the scientific field. My sincere thanks also goes to Mathias Sintorn, Senior R&D Specialist, for his insightful comments and absolute support to the thesis. I am most grateful to Prof. Markus Fiedler for his technical support and encouragement whenever I was in need. I would also like to thank my friends in Ronneby, Karlskrona and Stockholm for all the fun we have had during my stay in Sweden. Last, but by no means least, I would like to express the profound gratitude from my deep heart to my parents: Aruchamy and Lakshmi and my brother: Gopienathan for their love and continuous support - both spiritually and materially. ii Contents Abstract i Acknowledgement ii Contents iii List of Figures vi List of Tables viii List of Acronyms ix 1 Introduction 1 1.1 Scope . 1 1.2 Study Prerequisites . 2 1.3 Working Process . 2 1.4 Contribution . 3 1.5 Reader Guidance . 3 2 Background 5 2.1 3G Network Architecture . 5 2.1.1 WCDMA UMTS Components [27] . 5 2.1.2 Radio Network Controller (RNC) . 8 2.1.3 Radio Resource Management (RRM) . 9 2.2 Data Trace Analysis . 10 2.2.1 Trace Generation . 10 2.2.2 Trace Analysis . 12 2.3 Related Work . 16 iii 3 Research Methodology 19 3.1 Aim and Objectives . 19 3.2 Research Questions . 19 3.3 Research Methodology . 20 4 Traffic Data Analysis 22 4.1 Service Distribution . 22 4.2 IP Packet Characteristics . 23 4.2.1 Packet Sizes [SP]..................... 23 4.2.2 Inter-arrival Times [IP] . 25 4.3 Burst Characteristics . 26 4.3.1 Burst Inter-arrival Times [I B] . 27 4.3.2 Burst Durations [DB] .................. 29 4.3.3 Burst Sizes [S B] ..................... 31 4.4 Session Characteristics . 34 4.4.1 Duration of Sessions [DS] . 34 S 4.4.2 Data Volume Transmitted per Session [SA] . 35 4.4.3 Clean Service Traffic Percentage [C S] . 37 4.5 Summary . 38 5 RNC Buffer Modelling 40 5.1 Trace-Based Simulation Buffer Model . 40 5.2 Design Assumptions . 43 5.3 Transport Channels and State Transitions . 44 5.4 Effects of Buffering Delays and QoS . 46 5.5 Attained Buffer Levels . 48 5.6 Summary . 50 6 Results and Discussion 52 6.1 Idle buffer Characteristics during Dedicated Channel Transmission . 52 6.1.1 Empty Buffer Duration [De] . 53 6.1.2 Percentage of Emptiness in Buffer per DCH Session [Pe] 55 6.2 Radio Resource Utilisation in terms of Dedicated Channel Performance . 57 6.2.1 Achieved User Throughput on DCH [Ta] . 58 6.2.2 Dedicated Channel Utilisation [UDCH] . 60 6.3 Discussion of the Results . 62 6.4 Validity of the Results . 63 7 Conclusion and Future Work 65 7.1 Conclusion . 65 7.2 Future Work . 66 iv Bibliography 68 Appendix 71 A Sub-types of Services 72 v List of Figures 1.1 Working Process . 3 2.1 Simplified 3GPP UMTS network reference model . 6 2.2 UTRAN Components and Interfaces . 7 2.3 Overview of RNC in UTRAN connecting CN and UE . 8 2.4 Modes of RRC and CELL States of UE . 9 2.5 Differentiation criteria for services from the traffic logs [1] . 12 2.6 Essential terms and their definitions with respect to traffic [11] 15 3.1 Step-by-step flow of the research work . 21 4.1 Service Distribution . 23 4.2 Packet sizes for different services . 24 4.3 Inter-arrival times between packets for different services . 26 4.4 Inter-arrival time between bursts for different services . 28 4.5 Mean Inter-Arrival Time between Bursts . 29 4.6 Duration of Bursts for different services . 30 4.7 Average Burst Durations . 31 4.8 Burst sizes for different services . 32 4.9 Mean burst sizes for different services . 33 4.10 Durations of Sessions for different services . 35 4.11 Data Volume per Session for different services . 36 4.12 Mean Clean Service Traffic Percentage for different services . 38 5.1 Calculation of different parameters of the buffer model . 42 5.2 Flowchart of RNC buffer model in relation with queueing . 43 5.3 Switching between transport channels and UE State Transitions 45 5.4 Average Buffering Delays for different services . 47 5.5 Buffer filling levels for different services . 49 5.6 Average buffer levels for different services . 50 6.1 Idle Durations of Buffer during DCH transmission . 54 6.2 Average Idle Durations of Buffer during DCH transmission . 55 6.3 Empty Buffer Percentage during DCH sessions . 56 6.4 Average Empty Buffer Percentage during DCH sessions . 57 vi 6.5 Achieved Throughput on DCH transmission . 59 6.6 Average Achieved Throughput on DCH transmission . 60 6.7 Utilisation of Dedicated Channel for different services . 61 6.8 Average Utilisation of Dedicated Channel for different services 62 vii List of Tables 2.1 UE states and Transport Channels with corresponding achievable bit-rates [27] . 10 2.2 Sample tags captured from the traffic capturing tool . 14 5.1 QoS End-to-End Packet Delay Range for Different Services [13] 46 viii List of Acronyms CN Core Network CS Circuit Switched DCH Dedicated Channel DPCCH Dedicated Physical Control Channel DPDCH Dedicated Physical Data Channel DRX Discontinuous Reception ETSI European Telecommunications Standard Institute FACH Forward Access Channel FIFO First In First Out FTP File Transfer Protocol GBR Guaranteed Bit Rate GSM Global System for Mobile Communication IMEI International Mobile Equipment Identity IMSI International Mobile Subscriber Identity ISDN Integrated Services Digital Network LTE Long Term Evolution MS Mobile Station MSC Mobile Station Controller NBAP Node-B Application Part PS Packet Switched PSTN Public Switched Telephone Network QoS Quality of Service QoE Quality of Experience RAB Radio Access Bearer RACH Random Access Channel ix RAN Radio Access Network RLC Radio Link Control RNC Radio Network Controller RNSAP Radio Network Application Subsystem Part RRC Radio Resource Control RRM Radio Resource Management SF Spreading Factor SGSN Serving General Packet Radio Service Support Node SLA Service Level Agreement UE User Equipment UMTS Universal Mobile Telecommunications System URA UTRAN Registration Area UTRAN UMTS Terrestrial Radio Access Network VLR Visitors Location Register WCDMA Wideband Code Division Multiple Access x Chapter 1 Introduction Due to ever-increasing users and subsequent network capacity requirements, resource optimization techniques to ensure optimal use of radio resources in the network to achieve good service quality are under research.