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Master ThesisElectrical EngineeringDecember 2012

Analysis of Radio Access Network Buffer FillingBased on Real Network Data

Logabharathi Aruchamy

School of ComputingBlekinge Institute of Technology37179 KarlskronaSweden

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This thesis is submitted to the School of Computing at Blekinge Institute

of Technology in partial fulfillment of the requirements for the degree ofMaster of Science in Electrical Engineering. The thesis is equivalent to 20weeks of full time studies.

Contact Information

Author:Logabharathi AruchamyE-mail: logabharathi@gmail.com

External Advisor(s)

Tomas Lundborg,Systems Manager,Ericsson AB,Development Unit Radio-System andTechnology,Torshamnsgatan 33,164 80 Stockholm, Sweden.

Mathias Sintorn,Senior Specialist R&D,Ericsson AB,Development Unit Radio-System andTechnology,Torshamnsgatan 33,164 80 Stockholm, Sweden.

University advisor:

Prof. Markus Fiedler,School of Computing (COM)

School of ComputingBlekinge Institute of Technology371 79 KARLSKRONA SWEDEN

Internet: www.bth.se/comPhone: +46 455 385000SWEDEN

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Abstract

The 3G and 4G networks have drastically improved availability andquality in data transmission for bandwidth hungry services such as video

streaming and location-based services. As 3G networks are very widelydeployed, there exists increased capacity requirement and transportchannel allocation to simultaneous users under a particular cell. Due tothis reason, adequate resources are not available, which in turn degradesboth service quality and user experienced quality. This research aims atunderstanding the characteristics of buffer filling during dedicated channel(DCH) transmission under fixed bit-rate assumptions on a per-user leveltaking different services into consideration. Furthermore, the resourceutilisation in terms of empty buffer durations and user throughputachieved during dedicated channel transmission are also analysed fordifferent data services existing in the mobile networks. The traces are

collected from a real network and characteristics of the traffic are analysedprior to understanding its buffer filling in Radio Network Controller(RNC) during downlink data transmission. Furthermore, the buffer ismodelled with some series of assumptions on channel bit-rates andsimulations 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 fordifferent services, in turn yielding possible understanding on the existingtransport channel switching scenario. With the help of analysing the bufferfilling for different services and transport channel utilisation, we learn thatmost of the data services show low DCH utilisation of approximately

around 20% and also found to have 80% of the total DCH session durationwith empty buffer, causing sub-optimal radio resource utilisation.

Keywords: Traffic Characteristics, Radio Network Controller (RNC),Dedicated Channel (DCH) and Channel Switching.

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Contents

Abstract i

Acknowledgement ii

Contents iii

List of Figures vi

List of Tables viii

List of Acronyms ix

1 Introduction 11.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Study Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Working Process . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.5 Reader Guidance . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Background 52.1 3G Network Architecture . . . . . . . . . . . . . . . . . . . . 5

2.1.1 WCDMA UMTS Components [27] . . . . . . . . . . . 52.1.2 Radio Network Controller (RNC) . . . . . . . . . . . . 82.1.3 Radio Resource Management (RRM) . . . . . . . . . . 9

2.2 Data Trace Analysis . . . . . . . . . . . . . . . . . . . . . . . 102.2.1 Trace Generation . . . . . . . . . . . . . . . . . . . . . 102.2.2 Trace Analysis . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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3 Research Methodology 19

3.1 Aim and Ob jectives . . . . . . . . . . . . . . . . . . . . . . . 193.2 Research Questions . . . . . . . . . . . . . . . . . . . . . . . . 193.3 Research Methodology . . . . . . . . . . . . . . . . . . . . . . 20

4 Traffic Data Analysis 224.1 Service Distribution . . . . . . . . . . . . . . . . . . . . . . . 224.2 IP Packet Characteristics . . . . . . . . . . . . . . . . . . . . 23

4.2.1 Packet Sizes [SP] . . . . . . . . . . . . . . . . . . . . . 234.2.2 Inter-arrival Times [IP] . . . . . . . . . . . . . . . . . 25

4.3 Burst Characteristics . . . . . . . . . . . . . . . . . . . . . . . 264.3.1 Burst Inter-arrival Times [IB] . . . . . . . . . . . . . . 27

4.3.2 Burst Durations [DB

] . . . . . . . . . . . . . . . . . . 294.3.3 Burst Sizes [SB] . . . . . . . . . . . . . . . . . . . . . 31

4.4 Session Characteristics . . . . . . . . . . . . . . . . . . . . . . 344.4.1 Duration of Sessions [DS] . . . . . . . . . . . . . . . . 344.4.2 Data Volume Transmitted per Session [SS

A] . . . . . . 35

4.4.3 Clean Service Traffic Percentage [CS] . . . . . . . . . 374.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5 RNC Buffer Modelling 405.1 Trace-Based Simulation Buffer Model . . . . . . . . . . . . . 405.2 Design Assumptions . . . . . . . . . . . . . . . . . . . . . . . 43

5.3 Transport Channels and State Transitions . . . . . . . . . . . 445.4 Effects of Buffering Delays and QoS . . . . . . . . . . . . . . 465.5 Attained Buffer Levels . . . . . . . . . . . . . . . . . . . . . . 485.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

6 Results and Discussion 526.1 Idle buffer Characteristics during Dedicated Channel

Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . 526.1.1 Empty Buffer Duration [De] . . . . . . . . . . . . . . . 536.1.2 Percentage of Emptiness in Buffer per DCH Session [Pe] 55

6.2 Radio Resource Utilisation in terms of Dedicated ChannelPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576.2.1 Achieved User Throughput on DCH [Ta] . . . . . . . . 586.2.2 Dedicated Channel Utilisation [UDCH] . . . . . . . . . 60

6.3 Discussion of the Results . . . . . . . . . . . . . . . . . . . . . 626.4 Validity of the Results . . . . . . . . . . . . . . . . . . . . . . 63

7 Conclusion and Future Work 657.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

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Bibliography 68

Appendix 71

A Sub-types of Services 72

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List of Figures

1.1 Working Process . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 Simplified 3GPP UMTS network reference model . . . . . . . 62.2 UTRAN Components and Interfaces . . . . . . . . . . . . . . 72.3 Overview of RNC in UTRAN connecting CN and UE . . . . 82.4 Modes of RRC and CELL States of UE . . . . . . . . . . . . 92.5 Differentiation criteria for services from the traffic logs [1] . . 122.6 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 . . . . . . . . . . . . . . . . . . . . . . . 234.2 Packet sizes for different services . . . . . . . . . . . . . . . . 244.3 Inter-arrival times between packets for different services . . . 26

4.4 Inter-arrival time between bursts for different services . . . . 284.5 Mean Inter-Arrival Time between Bursts . . . . . . . . . . . . 294.6 Duration of Bursts for different services . . . . . . . . . . . . 304.7 Average Burst Durations . . . . . . . . . . . . . . . . . . . . . 314.8 Burst sizes for different services . . . . . . . . . . . . . . . . . 324.9 Mean burst sizes for different services . . . . . . . . . . . . . 334.10 Durations of Sessions for different services . . . . . . . . . . . 354.11 Data Volume per Session for different services . . . . . . . . . 364.12 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 . . 435.3 Switching between transport channels and UE State Transitions 455.4 Average Buffering Delays for different services . . . . . . . . . 475.5 Buffer filling levels for different services . . . . . . . . . . . . 495.6 Average buffer levels for different services . . . . . . . . . . . 50

6.1 Idle Durations of Buffer during DCH transmission . . . . . . 546.2 Average Idle Durations of Buffer during DCH transmission . 556.3 Empty Buffer Percentage during DCH sessions . . . . . . . . 566.4 Average Empty Buffer Percentage during DCH sessions . . . 57

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6.5 Achieved Throughput on DCH transmission . . . . . . . . . . 59

6.6 Average Achieved Throughput on DCH transmission . . . . . 606.7 Utilisation of Dedicated Channel for different services . . . . 616.8 Average Utilisation of Dedicated Channel for different services 62

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List of Tables

2.1 UE states and Transport Channels with correspondingachievable 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

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List of AcronymsCN Core NetworkCS 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

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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 NodeSLA 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

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Chapter 1

Introduction

Due to ever-increasing users and subsequent network capacityrequirements, resource optimization techniques to ensure optimal use ofradio resources in the network to achieve good service quality are underresearch.

Moreover, the performance of different services in the radio networkscenario in terms of network parameters such as user throughput, emptyRNC buffer periods and transport channel utilisation are very importantto understand the impact of poor resource usage on the system capacity.In addition, unwanted resource occupied by one user in a particular cell

leads to poor experienced quality for another user in the same cell due tomore delay, latency and jitter in the transmission, caused by inadequatechannel capacity.

With the help of some suggestions from [10], related to fundamentallimitations of the current state machine design with respect to statetransitions and down-switch timer in terms of system overhead andperformance, there is a need to emphasize further on performancevariations observed during the existence of traffic for different data servicesin RAN. In this research, considering different services and their trafficfrom real network traces, the buffer filling is analysed and performance

variations in terms of channel utilisation is studied.

1.1 Scope

The performance study conducted in this research will evaluate howdifferent services fill the RNC buffer in live networks with fixed channelbit-rate considerations. This will be determined by understanding thecharacteristics of input traffic data and different output parameters of the

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modelled buffer in terms of Cumulative Distribution Function (CDF),

mean values and confidence intervals (CI).

The report will demonstrate the obtained traffic characteristics, RNCbuffer model and finally illustrate the results obtained from the buffermodel with default channel bit-rate considerations, after supplying theepoch timestamps and corresponding packet sizes from real network tracesas input. The discussions will be made regarding the bursty behaviour ofthe traffic models, empty buffer behaviour and dedicated channelutilisation.

1.2 Study Prerequisites

For the work conducted in this research, the prerequisites needed were:

Knowledge of the networking protocols used in todays 3G and 4Gmobile networks.

Understanding of queuing theory and its application on teletrafficengineering and packet data networks.

Knowledge of statistical modelling and empirical data analysis withunderstanding related to cumulative distribution, mean, standard

deviation and confidence interval.

An initial study was conducted for four weeks during which a selectednumber of books and articles were read, which provided knowledge onmobile communication in general, the basics of 3G and 4G networks, thetransmission protocols, Radio Access Network (RAN) architecture andqueuing theory in general.

1.3 Working Process

The RNC buffer model makes a series of assumptions andapproximations on the behaviour of the mobile networks it is designed toemulate. According to these assumptions and the input traffic data, themodel estimates the empty buffer time and DCH utilisation for the usersusing different services. For achieving the outcomes, the working processas shown in Figure 1.1 is involved.

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Figure 1.1: Working Process

Further explanations on the research methodology and process flow willbe explained in detail in Chapter 3.

1.4 Contribution

The major contributions of this thesis work are as follows:

A methodology for evaluation of RNC buffer filling with real networktraces, taking different services into consideration.

Analysis of traffic data in terms of packet sizes and inter-arrival timesfor different services and its performance variations during dedicatedchannel transmissions.

Presentation of results in terms of empty buffer time, user throughputand transport channel utilisation obtained from modelled buffer tounderstand radio resource utilisation with respect to RNC buffer anddedicated channel for different services.

1.5 Reader Guidance

The remainder of the report is organised as follows. The backgroundinformation, key concepts covering 3G network architecture, data traceanalysis and related work are explained in Chapter 2. Chapter 3 describesthe aim and objectives, followed by the research questions and researchmethodology.

In Chapter 4, the traffic data analysis from the obtained real networktraces for different services is covered. The RNC buffer modelling withdesign assumptions and validations are explained in Chapter 5 and

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subsequent results are discussed in Chapter 6. Finally key conclusions with

potential future directions of the research are explained in Chapter 7.

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Chapter 2

Background

2.1 3G Network Architecture

The Universal Mobile Telecommunication Systems (UMTS) is designedto have flexible delivery of any type of service with no requirement ofnetwork optimisation for each service [27]. UMTS is evolving to cope withever-increasing need of wireless data services such as multi-mediamessaging, video streaming, location based services, mobile commerce andon-line gaming.

This section is organised as follows, Section 2.1.1 explains essential

components of WCDMA UMTS network briefly, followed by Section 2.1.2about Radio Network Controller (RNC) and its modes of operation interms of buffer behaviour and Section 2.1.3 covers Radio ResourceManagement (RRM) present in UTRAN for resource control mechanisms.

2.1.1 WCDMA UMTS Components [27]

According to the 3GPP reference network model, UMTS consists of fourmajor network components as follows:

User Equipment (UE)

Radio Access Network (RAN)

Core Network (CN)

External Network (e.g., IP networks, PSTN/ISDN)

The UE is the end-user electronic device such as Android/iPhone, iPad orPC dongle connected to the network through Mobile Station (MS). Inaddition, the data bandwidth of the UE is significantly limited by thebattery capacity of UE due to MS power consumption during wireless datatransmission [18].

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In 3GPP and ETSI, the RAN is termed as UTRAN (UMTS TerrestrialRAN) and this network part is of our research interest. Severalcomponents making up this network will be explained to understand howbits are transmitted over the radio interface.

Figure 2.1: Simplified 3GPP UMTS network reference model

The core network is similar to the GSM network having

packet-switched or circuit-switched domains according to externalnetworks such as PSTN/ISDN or IP networks respectively. In addition,the CN is responsible for switching/routing calls and data connections toexternal networks, whereas RAN handles all radio-related functionality.

As far as RAN is considered, it is essential to understand thefunctionalities of the following components,

Radio Base Station (Node B)

Radio Network Controller (RNC)

Interfaces

Node BThis provides air interface L1 processing such as channel coding and

interleaving, rate adaptation, spreading and so on. Some of the radioresource management functions like inner loop power control are alsocarried out by Node B.

Logical functionalities of RNCLoad and congestion control of its own cells and execution of admission

control and code control for new radio links to be established are handled

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by the Controlling RNC (CRNC). Whereas, Serving RNCs (SRNC)

perform L2 processing of data to/from the radio interface, mapping ofRadio Access Bearer (RAB) parameters into air interface transportchannel parameters, hand-over decisions and outer-loop power control.

In the same way, the Drift RNCs (DRNC) control cells used by themobile, macro diversity combining and splitting. A single RNC normallycontains all the CRNC, SRNC and DRNC functionalities.

UTRAN Interfaces

Figure 2.2: UTRAN Components and Interfaces

1. UTRAN-CN (Iu)As can be seen from Figure 2.2, Iu has two different instances, whichdiffer according to the type of external network. If the externalnetwork is a circuit-switched (CS) network consisting of MobileSwitching Center (MSC)/Visitors Location Register (VLR), theinterface is termed Iu-CS. On the other hand, Iu-PS is used in case of

a packet-switched (PS) network with Serving General Packet RadioServices Support Node (SGSN). Another interface, Iu Broadcast(Iu-BC), is used for the Broadcast domain of CN, which is not shownin Figure 2.2.

2. RNC-RNC (Iur)This interface is primarily to enable inter-RNC soft handover, but ithas some additional functionalities such as

(a) Inter-RNC mobility;

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(b) Dedicated channel traffic handover;

(c) Common channel traffic handover;

(d) Global resource management.

The signalling protocol is Radio Network Subsystem Application Part(RNSAP) and it is possible to implement any one of the four Iurmodules between two RNCs, according to operators requirements.

3. RNC-Node B (Iub)In case of the Iub interface, traffic termination is one of the mainfunctions and the signalling interface is Node B Application Part(NBAP), which is divided into common NBAP (C-NBAP) for

signalling procedures across common signalling links and dedicatedNBAP (D-NBAP) used in dedicated signalling links.

4. Node B-UE (Uu)Finally, the Uu interface is between the RAN and UE, which with thehelp of MS, transmits data over the radio interface.

2.1.2 Radio Network Controller (RNC)

The RNC plays an important role in maintaining the proper flow ofdata according to available bit rates over the radio link. Moreover, thereare several protocols, which make this process easier to control, as there is

a large number of users sharing a particular RNC. It owns and controls theresources in the radio network in its domain and also manages theconnections to UE [27].

Figure 2.3: Overview of RNC in UTRAN connecting CN and UE

As shown in the Figure 2.3, the RNC processes the packets receivedfrom CN by queuing the packets and transmitting with a defined bit-rate,

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which is dependent on the radio link allocation for the user based on the

service level agreement (SLA) agreed between the service provider and theusers. However, the attained bit-rates vary over time due to varyingnetwork conditions, transport channel availability and number of userswithin a particular cell.

2.1.3 Radio Resource Management (RRM)

RRC messages in terms of handovers, cell updates and measurementsbetween UE and UTRAN are performed by the RRM functionalities presentin the RAN. There are two basic modes of operation: idle and connectedmode.

Figure 2.4: Modes of RRC and CELL States of UE

IdleDuring idle mode, the UE can receive system information and

broadcasting messages through RRC signaling, but UTRAN has noconnection with UE at this point and does not have any information aboutthe idle mode UEs. However, the connection can be created throughpaging (network initiated) or random access (UE initiated).

ConnectedOn the other hand, during connected mode, there can be four possible

states such as CELL DCH, CELL FACH, CELL PCH and URA PCH asshown in Figure 2.4. In these states, CELL represents the current cell,URA represents the UTRAN Registration Area, under which the RNC canlocate the UE. Furthermore, the UE can transmit or receive data throughany of the following transport channels as shown in Table 2.1.

During the CELL DCH state, DCH is allocated for the user, which canbe mapped to physical channels such as Dedicated Physical Data Channel(DPDCH) or Dedicated Physical Control Channel (DPCCH). This hashigher transmission rates to provision high bandwidth services.

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Conversely, during low bit-rates, UE is forced to CELL FACH state.

Thus data transmission is achieved through FACH having low bit rates asthe channel is shared.

In the CELL PCH state, the user can be contacted through PCH andthe user is known on the cell level in this state. This same scenario isapplicable in URA PCH, except that the user can be known on URA leveland paging is over the entire URA.

The channel-switching functions are carried out by Radio ResourceManagement (RRM) function through Radio Resource Control (RRC)protocol messages. In other words, the UE will be assigned appropriate

transport channels, and the data rate is controlled, through RRM.

Table 2.1: UE states and Transport Channels with corresponding achievablebit-rates [27]

UE State TransportChannel

Practical Bit-Rates

CELL DCH DedicatedChannel(DCH)

High, up to 2 Mbps

CELL FACH ForwardAccessChannel(FACH)

Low, up to 64 kbps

CELL PCH/URA PCH PagingChannel(PCH)

Only Signalling/Paging

2.2 Data Trace Analysis

This part is organised as follows, Section 2.2.1 explains the way inwhich the traces i.e. traffic data are collected and their properties we

determined and Section 2.2.2 covers the important terms used in thereport to understand the analysis and how the traffic data analysis on peruser basis is performed for different services.

2.2.1 Trace Generation

To address the characteristics of the buffer filling for different servicesin the RNC of UTRAN, traces are collected from an operating 3G networkin a major American city. In addition, the data is collected at the interfacebetween CN and RAN, i.e. Iu-PS using a traffic capturing tool, which is an

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Ericsson tool set to measure and analyse IP traffic.

Furthermore, it processes and classifies traffic online and instead of fulltraces, only stores traffic statistics at various levels of detail. It should alsobe noted that the delay or jitter between CN and RAN (which is in theorder of a few ms) is not expected to have relevant impact on the study.

This tool classifies the user plane traffic using a set of rules andassociated decision logic defined in an XML file. So, during evaluation ofthe rules, payload of incoming packets is matched against each rule. Inaddition, the set of rules are freely modifiable and extensible and it alsoprovides a way to filter or process the complete measurement data along

pre-defined aspects. For this, each user data flow may have zero or moretags attached to it, as defined by the classification rules.

The traces are collected for every single minute interval for 2 dayscontinuously, which resulted in 2880 trace files each having file size ofaround 5000 kB containing traces of the packet data traffic and it shouldbe noted that there is no voice data collected, and that packet trafficinformation is collected from 3G network only.

In addition, each packet is identified using timestamps, TCP/UDPsession, source IP address and port number, destination IP address and

port number, uplink/downlink, encoded International Mobile SubscriberIdentity (IMSI), International Mobile Equipment Identity (IMEI) andservice tags.

It should be noted that the link bit-rates exhibited in the radio networkare not known. Furthermore, the information on the network policycontrol framework of the network was not possible to obtain because ofsensitivity of the information from the mobile operators point of view.

So assumptions on channel bit-rates are made and buffer fillings underthis scenario for different services are studied.

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2.2.2 Trace Analysis

Figure 2.5: Differentiation criteria for services from the traffic logs [1]

1. QoS ClassesThe QoS class is the differentiation of services in terms of whether ithas guaranteed bit-rate or not in the radio network. Each service hasits own traffic parameters according to QoS differentiation in terms

of priority, packet delay and packet error loss rate. In Section 5.4,the QoS packet delay parameter for each service will be explained indetail.

From the bit-rate considerations observed in the real networkscenario, the Guaranteed Bit-Rate (GBR) bearer carries traffic thatrequires a minimum bit-rate guarantee from the network, while thenon-Guaranteed Bit Rate (non-GBR) bearer carries variable bit-ratetraffic and is offered as best-effort service by the network [11].

As shown in the Figure 2.6, the conversational and streaming

services, which are real-time or GBR services need low packet delayand loss ratio. On the other hand, non-GBR services such asbackground services are considered to be delivered with best effort.

Moreover, as the research is related only to the data services in thewireless networks, the conversational services such as voice or videocalling are not considered.

2. ServicesThe traffic data collected has different services, but to reduce the

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complexities, all the major services are only taken out from the trace

files. The service here is termed as functionality in the trafficcapturing tool, which will be an essential parameter to differentiatethe packet when it is collected.

According to 3GPP 23.107, the services are differentiated accordingto their QoS in the following way to understand their characteristicsrelated to this research separately. However, the extent of QoS basedprioritization in the input traces is not known. Moreover, this is notrelevant for the study, since the analysis is considered with a singleuser at a time.

(a) GBR Streaming

video-playback

audio-playback

media-playback

(b) Non-GBR Interactive

instant-messaging

gaming

web-browsing

social-networking

maps

(c) Non-GBR Background email

file-download

advertisement

software-update

file-sharing

It should be noted that media-playback is the real-time streaming withprotocols such as RTP, RTSP, whereas video and audio-playback arebuffered streaming with HTTP protocol.

3. Service Sub-Types

Furthermore, the tags that are attached to flows are grouped intofacets, representing different aspects of the traffic. Facets include

FunctionalityThe functionality or service tells the activity type for which theflow is used and this comprises of social-networking,web-browsing, instant-messaging, gaming, maps,software-update, file-download, email, video-playback,audio-playback, media-playback and advertisement.

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Protocol

This tells the protocol carrying this flow such as HTTP, FTP,XMPP, SIP, SSH, RTSP and RTP.

Service-providerThere are several service providers, who provide services ondifferent functionalities such as Google providing email,web-browsing and maps services. So this tells whichservice-provider is behind the flow, if there existsservice-provider information in the packet data.

Client-applicationSimilar to service providers, the same service can be accessed

through different applications such as web-browsing throughMozilla Firefox, Chrome or Internet Explorer.

EncryptionMost of the secure services need encryption, so as to ensure thedata security in terms of confidentiality, integrity andauthenticity by enabling SSL for the data transmission. Thedata security and protection in the radio network is achievedthrough Packet Data Convergence Protocol (PDCP), whichprovides header compression algorithms for IP packets. Inaddition, these algorithms can be negotiated during RRC RadioBearer (RB) establishment or reconfiguration procedures [27].

EncapsulationAdditionally, encapsulation is also found in some services tosecure the transmission further to protect the data fromintruders.

For example a flow can be characterised like sample tags given in theTable 2.2.

Table 2.2: Sample tags captured from the traffic capturing toolprotocol functionality service-

provider

client-

application

encryption

HTTP social-networking

Facebook Mozilla-Firefox

SSL

HTTP video-

playback

Apple iPhone-

Media-Player

-

RTSP media-

playback

- - -

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Figure 2.6: Essential terms and their definitions with respect to traffic [11]

4. IP PacketsThe major information of IP packets from the traces such as epochtimestamps and IP packet sizes will be analysed for anyregularities/irregularities in the traffic flow for different services.

5. BurstsIt is important to understand the term bursts, which is assumed tobe a set of one or more IP packets arriving with inter-arrival timeless than 200 milliseconds as shown in Figure 2.6. Even if it is asingle packet with no packets accompanying it with inter-arrival time

less than 200 ms, then that particular packet is also considered as aburst.

It should be noted that, the inter-arrival time of packets within aburst can be assumed with different values other than 200 ms such as2 s, 5 s or 10 s and so on for different services depending on theassumptions on user behaviour, but it is assumed to have a fixedvalue in this study i.e. 200 ms for all the services to reducecomplexity in comparison and analysis. In addition, this value isassumed only after prior understanding of the packet inter-arrivals

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and related analysis on the traffic data. So, if the packet inter-arrival

time is more than 200 ms, then it will be considered as the end of thecurrent burst or start of the next burst.

It is interesting to know about the characteristics of the bursts interms of inter-arrival times, duration and size of bursts for differentservices in the radio network scenario. In addition, numerousresearch work state the principle of bursty behaviour in packetarrivals for most TCP services, rather than regular inter-arrivals ofpackets.

6. Sessions

For a single user, there may be continuous flow of packets for acertain time period or intermittent gaps between the packet flows,when a single service is considered. Thus, as shown in Figure 2.6, asession is termed as the traffic during downlink data transmissionwith no inactivity for about 300 seconds. If there is such aninactivity, the session is assumed to terminate and new session forthe same user starts again with arrival of packets belonging to thesame service considered.

7. UsersIf a particular service is considered, the whole trace file is checked withthe help of tags, for the users who use this service. This information

is used for further investigating into the flow of packets towards theuser for different services.

After the differentiation of services with the aforementioned criteria, theresearch is carried out on analysing several parameters both from the trafficand buffer model implemented. Finally, the analysis of essential parametersto understand the radio resource utilisation is also made.

2.3 Related Work

The ever-increasing need for high-bandwidth applications accessiblethrough 3G and LTE networks widens the research opportunities inanalysing existing network scenario and identifying possible qualityenhancements and resource optimization procedures in the radio networks.In addition, there are various work related to performance measurementswith the help of emulation of a real network and analysis of severalparameters involving quality improvements in the wireless networks.

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RNC Buffer Related Work

In [19], analysis of TCP performance with respect to RLC buffer size isanalysed, with the help of simulations carried out resembling the real radionetworks and there are reflections of TCP congestion control mechanismssuch as slow start (exponential growth) and congestion avoidance (lineargrowth). The ETSI discrete event simulation model is proposed to studythe Discontinuous Reception (DRX) mechanism exercised between thenetwork and MS to study the inactivity timer threshold and DRX cycle[14]. In addition, the expected waiting times, queue length and powersaving factor are also analysed in [14].

A research work related to usability of instant messaging service over a3G WCDMA network gives the technical performance analysis andusability evaluations of the radio network controller under differentnetwork set-ups [25]. An analysis related to link throughput according tochanges in the buffer size by varying TCP flavour (Tahoe, Reno, NewRenoor SACK), FTP file size, RLC buffer size and DCH data rates is conductedin [23]. The performance of TCP over dedicated channels with different bitrates and different transmission time intervals (TTI) is examined tounderstand end-to-end packet delay, delay in the radio access network andthroughput in the wireless link [17].

RRM Related WorkThe findings in [10] suggest the fundamental limitation of the current

state machine design with respect to transitions and timer values in UMTSnetwork. The up-switching threshold (bytes) and down-switching timer(seconds) for transport channel switching are considered to be staticleading to consideration of all traffic with same characteristics leading tothe difficulty in balancing the trade-off between network essentials in termsof network management, system overhead and performance.

Some of the accessibility issues such as termination failures andfrequent user registrations are studied to understand the performance of

the network according to user types and device types in [9].

In addition, resource utilization in terms of channel switching is animportant consideration, under which there are various algorithmsproposed to meet the specifications of RNC and evaluations are made withthe help of simulations. Furthermore, several impacts of parameter settingson performance with respect to packet loss probability and utilisation ofdedicated channels are analysed in [16]. Moreover, the behaviour ofNon-Real-Time sessions and channel switching are evaluated with the help

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of blocking rate, mean packet delay and cell throughput to decrease the

number of blocked calls keeping other metrics at a satisfactory level [24].

Even though there are numerous works in the radio resource andperformance analysis, this research aims at studying in detail the RNCbuffer filling with fixed channel bit-rate conditions, taking the most widelyused data services existing in wireless 3G and LTE networks intoconsideration.

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Chapter 3

Research Methodology

This chapter is organised as follows: Section 3.1 explains the aim andobjectives, Section 3.2 gives the guiding questions to be addressed andmotivation behind the research and Section 3.3 describes the researchmethodology handled in order to fulfil the goals of the thesis work.

3.1 Aim and Objectives

The goal of this thesis work is to investigate how traffic from real,operating networks impacts the buffer filling in the radio network nodes.The objectives to achieve this goal are to

analyse packet traces from real networks;

fit a parameterized model of IP packet inter-arrival times and IPpacket sizes to the existing packet traces, taking into accountdifferent services;

implement and analyse different parameters of the RNC buffer model;

evaluate buffer filling for users using different services in the radionetwork, in terms of resulting parameters of the model;

with the resulting level of buffer filling, analyse radio resourceutilization and radio network performance in terms of RNC bufferand DCH parameters for different services.

3.2 Research Questions

The leading questions that should be addressed in this research work are

RQ 1: What are the variations in terms of inter-arrivals, durationsand size of bursts of IP packets for different services?

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RQ 2: How long does the RNC buffer show empty buffer levels during

DCH transmission for different services?

RQ 3: How do different services perform on dedicated channel datatransmission in terms of user throughput and channel utilisation?

The first question is mainly to find out the distribution of the trafficmodels supplied to the buffer as input to understand the characteristics ofthe data traffic obtained.

The second question is framed to address how different services incurempty durations in the RNC buffer due to intermediate inactivity duringdedicated channel transmission according to the channel bit-rate

conditions assumed. In addition, this is essential to gather informationabout the performance of different services in the radio network in terms ofbuffer utilisation.

From the third question, the analysis will reflect the radio resourceutilisation with respect to dedicated channel for different services.

3.3 Research Methodology

The research work comes under the category of empirical data analysis

and it deals with traffic data analysis of obtained traces with respect todifferent services and further investigation related to the radio network bufferfilling for different services. The following describes the steps carried out toobtain the necessary outcomes of this research as shown in Figure 3.1.

1. The data traffic is analysed to get the knowledge of obtainableparameters from the trace files.

2. The traces are classified according to different services so as to beanalysed further in terms of important parameters of the traffic andthis is mentioned in Section 2.2.

3. From the traces, the packet sizes and inter-arrival times are examinedfor different services and bursts of the data traffic is also analysed, soas to understand the regularities or irregularities of bursts in trafficfor different services.

4. The RNC buffer is modelled with a series of assumptions andapproximations to understand how buffer performance is affected bydifferent services in a real RNC.

5. The obtained traffic separated as sessions for different services aresupplied as input to the buffer to evaluate the buffer filling.

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6. To validate the buffer model, the buffer levels achieved and packet

delays occurred due to buffering are estimated for different services.

7. During DCH transmission, the empty buffer times and percentage ofempty time durations are obtained for different services and this helpsto understand how different data services perform in the radio networkscenario.

8. The radio resource utilisation is studied in terms of obtained userthroughput and channel utilisation on the DCH link for differentservices from the buffer model.

Figure 3.1: Step-by-step flow of the research work

In [10], real network traces are used for evaluating the improvement ofenergy levels in the UE by leveraging an existing feature called fastdormancy supported by 3GPP specifications. The real network traces

obtained for our research work contain additional details in terms of trafficparameters to understand the buffer filling at radio network part fordifferent data services.

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sessions for all the services. As can be seen from the Figure 4.1,

web-browsing, social-networking, instant-messaging and email show acomparatively large number of sessions.

0

20

40

60

80

100

TotalDataVolume[%]

TotalNumberofSession[%]

TotalSessionDuration[%]

%o

ftotal

Details of Service Sessions

YouTubeweb-browsingvideo-playbacksoftware-updatesocial-networkingmedia-playbackmapsinstant-messaginggamingfile-sharingfile-download-.*-iTunes-iTunesfile-download-.*-Android-Market-Android-Marketemailaudio-playbackadvertisement

Figure 4.1: Service Distribution

Total Session Duration [%]In addition to the above analysis related to total data volume [%] andtotal number of sessions [%], the total session duration [%] for differentservices is also important. It is calculated from the ratio between theduration of all the sessions of a particular service and total sessionduration of all the services. It is evident from the Figure 4.1 that,web-browsing, social-networking, instant-messaging, email andadvertisement show longer durations of sessions than other services. Thisis similar to that of the total number of sessions [%].

In short, all the streaming, web-browsing, maps and file-download

services have shorter session durations and lower number of sessions, buttransmit larger data volume than social-networking, instant-messaging,email and advertisement services.

4.2 IP Packet Characteristics

4.2.1 Packet Sizes [SP]

The characteristics of the traffic flow can be understood from thepacket sizes and inter-arrival times for different services.

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Figure 4.2 gives an overview of packet sizes in the form of CDF plot,from which almost all GBR streaming services are found to have 80% ofpacket sizes on 1448 bytes, other than media-playback which has varyingpacket sizes between 52 and 1448 bytes.

Figure 4.2: Packet sizes for different services

In case of non-GBR interactive services such as gaming,instant-messaging and social-networking, 60% packet sizes are found to be52 bytes, whereas web-browsing and maps show packet sizes of 1448 bytes

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for roughly 70% of the values.

So there exists notable diversity within this group and this may be dueto the services such as web-browsing and maps sending large chunks ofdata towards the user. On the other hand, services such asinstant-messaging and social-networking send small chunks of data most ofthe time, when the user is connected to the network and accessing theseservices.

Similar behaviour to that of streaming services is observed in case offile-download and software-update services, whereas advertisement andfile-sharing show packet sizes of 52 bytes in 50% of the values. It is

interesting to look at the file-sharing services, which show small packetsizes probably due to signalling in the network.

4.2.2 Inter-arrival Times [IP]

As can be seen from Figure 4.3, similarities among services in termsof inter-arrival times are observed. It is evident from the Figure 4.3 thatroughly around 70% of inter-arrival times are less than 200 ms for almost allthe services and this implies that there are more packets as bursts, accordingto our assumptions, from the traffic data obtained.

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Figure 4.3: Inter-arrival times between packets for different services

4.3 Burst Characteristics

It is important to evaluate the characteristics of bursts of packets fordifferent services, before analysing the buffer filling at the radio network,in order to get a clear picture on the data volume sent as packet bursts.This might vary with respect to different services. This analysis has beencarried out based on the assumption of burst inter-arrival times greaterthan 200 ms.

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Thus the first research question on analysis related to bursts, isaddressed in this section. This deals with the study of bursty behaviour ofpacket arrivals in terms of burst inter-arrival times, durations and sizestaking different services into consideration.

4.3.1 Burst Inter-arrival Times [IB]

The formula used for calculating this value is as follows,

IBn = t

Bs,n t

Be,n1 (4.1)

where,

IBn - Inter-arrival time of burst n in seconds

tBs,n - Epoch time stamp of first packet or start of current burst

tBe,n1 - Epoch time stamp of last packet or end of previous burst

It should be noted that, the inter-arrival times between bursts have aminimum value of 200 ms, below which the packets are considered asbursts. In addition, there is a maximum value of 300 seconds, above whichthe session is considered to be terminated and new session will commence

with arrival of packets of the service considered.

It can be observed from Figure 4.4 that GBR-streaming services,interactive services except instant-messaging and background servicesexcept advertisement and file-sharing show most of the inter-arrival timesbetween bursts less than 1 second.

Moreover, instant-messaging and advertisement have roughly 60% ofthe burst inter-arrival times less than 1 second. However in case offile-sharing, there is only 40% of the inter-arrival times are less than 1second.

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Figure 4.4: Inter-arrival time between bursts for different services

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advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 2 4 6 8 10 12 14

Services

Inter-Arrival of Bursts [seconds]

Mean Inter-Arrival Time between Bursts

Figure 4.5: Mean Inter-Arrival Time between Bursts

In addition, the mean value of the burst inter-arrivals are calculated withthe confidence intervals as shown in the Figure 4.5, which has most of theservices showing the inter-arrival time roughly around 1 second, which isrelatively high in case of instant-messaging and file-sharing having values

more than 5 seconds.

4.3.2 Burst Durations [DB]

It is important to understand the duration of how long the burst existsfor different services, which may be regular or irregular according to the typeof service and also the conditions in the network during data collection. Thisis calculated from the formula,

DBn = t

Be,n t

Bs,n (4.2)

where,

DBn - Duration of burst n in seconds

tBe,n - Epoch time stamp of last packet or end of current burst

tBs,n - Epoch time stamp of first packet or start of the current burst

From the Figure 4.6, media-playback is found to have short duration ofbursts i.e. less than 1 ms in roughly around 50% of the values. This mightbe because of real-time streaming causing short duration of bursts or

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individual packet arrivals in case of media-playback.

As shown in Figure 4.6, most of the other services show a duration ofbursts in the range of 200 ms and 1 second, which is observed in more than70% of the bursts for almost all the services except advertisement andsoftware-update, which show around 40% of the burst durations more than1 second.

Figure 4.6: Duration of Bursts for different services

In addition, from the Figure 4.7, the mean and confidence interval

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implies that most of the services have duration of bursts less than 5

seconds, but advertisement and software-update show comparatively longburst durations.

advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 50 100 150 200 250 300

Services

Duration of Bursts [seconds]

Mean Duration of Bursts

Figure 4.7: Average Burst Durations

4.3.3 Burst Sizes [SB

]The constraint that groups the packets m,m+1...m+N in a single burst,

is that every packet fulfils the following condition,

tPm+1 t

Pm < 200 ms (4.3)

where,tPm+1 - Epoch timestamp of the next packet, in seconds

tPm - Epoch timestamp of the current packet, in seconds

Even though most of the services show almost similar behaviour interms of burst inter-arrivals and durations, the size of bursts are found tovary according to the type of service. This value is calculated as follows:

SBn = S

Pm + S

Pm+1 + + S

Pm+N (4.4)

where,SBn - Data Volume or Size of the burst n, in bytes

SPm...SPm+N - Size of each packet from m to m+N (m+N is the total

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number of packets in the burst), in bytes

Figure 4.8: Burst sizes for different services

As shown in Figure 4.8, GBR streaming services such as audio andmedia playback show around 80% of the burst sizes in the range of 1448bytes and 10 kB, whereas video-playback is found to have around 80% ofthe burst sizes between 1 kB and 1 MB. The reason behind thischaracteristics emphasizes the larger contents sent as bursts in case of

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video-playback than the audio and media-playbacks.

In contrast, non-GBR interactive services such as instant-messagingand gaming have most of the bursts in the range of 52 and 1448 bytes,which is because of single packets as bursts most of the time. However,maps, social-networking, web-browsing, email, advertisement andsoftware-update show burst sizes between 100 bytes and 100 kB in roughly70% of the values.

Conversely, file-sharing service is observed to have lower burst sizesmost of the time showing less than 100 bytes of burst sizes in 70% of theobtained values, which is contradictory to file-download iTunes showing

40% and file-download-Android showing roughly around 80% of the burstsizes in the range of 1 kB and 10 kB.

Eventhough the presumption was like all the file-download serviceshave similar characteristics in downloading, the obtained results fromburst sizes for different services show varying characteristics.

advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 50 100 150 200 250

Services

Burst Sizes [KB]

Mean Burst Sizes

Figure 4.9: Mean burst sizes for different services

From the Figure 4.9 above, most of the services have burst sizes less than50 kB, but GBR streaming services except media-playback have bursts ofsizes between 50 and 100 kB and software-update service has larger burstsin the range of 100 to 200 kB.

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4.4 Session Characteristics

4.4.1 Duration of Sessions [DS]

The following analysis is related to understanding the length of sessionsfor different services. From the following Figure 4.10 showing the durationof sessions in minutes, it is evident that almost all the services have mostof their session durations approximately less than 100 minutes.

It is interesting to note that, around 70% of the streaming andfile-sharing services show session durations between 1 and 100 minutes,which is higher than interactive services and background services.

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Figure 4.10: Durations of Sessions for different services

4.4.2 Data Volume Transmitted per Session [SSA

]

For each session the data volume transmitted in kB is calculated bysumming up the IP packet sizes during that session for different services.

From the following Figure 4.11, the GBR streaming services are foundto have 70% of the sessions with data volumes in the range of 10 kB and100 MB.

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Figure 4.11: Data Volume per Session for different services

Conversely in case of non-GBR interactive services, instant messagingshows around 80% of the sessions with session data volume less than 10kB, followed by gaming and social-networking with 80% session datavolume in the range of 1 kB and 100 kB. However, maps and web-browsingservices show around 60% of the sessions with data volumes between 10 kBand 10 MB.

In case of background services roughly around 80% of the sessions havesession data volumes below 100 kB, other than file-download-Android

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showing 70% of the sessions having data volume ranging from 1 MB to 10

MB, which is observed to transmit highest volumes of data per sessionfrom the obtained traces.

From the analysis related to session data volumes, it is clear thatGBR-streaming services achieve larger data volumes than other services,which may be because of the bulk data sent towards the user during eachsession in terms of streaming services.

4.4.3 Clean Service Traffic Percentage [CS]

It should be noted that the traffic data considered for different services,

may possess other services also in the bursts of packets, due tosimultaneous access of different services at the user side.

Moreover, the interest on clean traffic percentage is mainly due toimprove the understanding on how traffic data for different services showclean service packets in the bursts. In other words, there are possibilitiesthat the bursts of packets of a particular service may have a few packetsbelonging to other services.

So, the percentage of packets belonging to a particular service during asession is calculated to understand this value from the obtained traffic

data. Here, the term session has the same definition as mentioned inSection 2.2.2. This also helps us to ensure how reliable different trafficdata from the traces, representing the services under consideration.

This is calculated by finding the ratio between amount of datatransmitted as clean service packets only during a session SSC and totaldata volume transmitted during the session SSA.

CS =

SSC

SSA

100% (4.5)

where,CS - Clean Service Traffic Percentage per session

SSC

- Amount of data transmitted as clean service packets per session

SSA

- Total data volume transmitted or summation of all packet sizes persession as explained in Section 4.4.2

So, the higher the value of CS, cleaner the service is. The mean cleanservice traffic percentage is calculated for each service and the 95%

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confidence interval is plotted in the Figure 4.12 below, showing most of the

services achieve CS

greater than 75%.

advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 20 40 60 80 100

Services

Clean Bursts [%]

Percentage of Clean Bursts per User Session

Figure 4.12: Mean Clean Service Traffic Percentage for different services

4.5 Summary

To put it in a nutshell, the traffic data analysis is essential to

understand the behaviour of the flow of traffic for different services interms of packet sizes, inter-arrival times, bursts and sessions. Some of thepoints to remember from this analysis are as follows:

Packet sizes obtained from the traces are mostly 52 and 1448 bytes,for which different services share these sizes in different proportions,depending on their corresponding data volume transmitted.

In case of inter-arrival times, except file-sharing, which hasapproximately 60% of its inter-arrival times greater than 200 ms,other services show lower inter-arrivals than 200 ms most of the timeleading to conclusion that large number of packets are transmitted as

bursts of packets with our assumption of 200 ms.

When it comes to bursty behaviour of the TCP traffic, most of theservices show bursty arrival of packets in 90% of the traces.Furthermore, services such as advertisement, software-update andgaming show higher proportion of mixture of other services also inthe bursts than other services. However, most of the sessionsconsidered for different services show more than 75% clean servicepackets and helpful for analysis on each service separately.

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Most of the user sessions considered are found to have their durations

below 1 hour, but still there are some sessions which last for longerdurations than an hour.

The total data volume transmitted to the users during their sessions isdependent on the type of traffic, since different services have varyingsize in the amount of data sent. Thus, there exist relatively high datavolumes in case of streaming and file-download services.

For the subsequent study on buffer filling, the analysis related to burstcharacteristics is of major importance, because it is helpful inunderstanding the traffic data filling buffer, given the inter-arrival timesand sizes of bursts. Moreover, the traffic profiles for different services and

their properties in terms of several parameters serve the purpose ofdeducing their traffic behaviour in the radio networks in general.

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Chapter 5

RNC Buffer Modelling

This chapter is organised as follows: Section 5.1 gives an overview on howthe buffer is modelled explaining how the input from the obtained traces ishandled, and an example scenario to understand how the output parametersare estimated from the buffer model. Section 5.2 explains the major designassumptions and approximations made for the buffer model. Section 5.3describes the transitions in the play-out rates of the RNC buffer due to linkbit-rate considerations when there is a switching between channels. Section5.4 is intended to provide the validation of the model by explaining thepossible packet buffering delays and how it conforms with QoS packet delaybudget for different services. Finally, Section 5.5 describes the achieved

buffer levels and its relationship with the burst sizes for different services.

5.1 Trace-Based Simulation Buffer Model

The real network data obtained has been differentiated intosession-wise traffic data files for each service. In addition, as mentionedbefore sessions are active periods containing downlink data traffic for usersunder each service.

From this traffic data, each packet data in terms of epoch timestampand packet size for different services is given as input to the buffer.However, each packet will be serviced according to the bit-rate in thechannel existing at that particular moment of packet arrival.

The UE is considered to be Idle during every session initiation and themajor parameters affecting buffer filling are the channel bit-rates andswitching considerations, which are set as default for our study.Furthermore, according to the 3GPP Release 7 as mentioned in [27] theconditions for channel switching and bit-rates for both dedicated channel(DCH) and forward access channel (FACH) in the pseudo code are

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as follows:

At the point of a packet arrival,

INITIAL CONDITIONS

If UE is Idle:

Channel = DCH and TransmissionRate = 512 kbps;

If UE is not Idle and Channel == DCH:

TransmissionRate = 512 kbps;

If UE is not Idle and Channel == FACH:

TransmissionRate = 16 kbps;

CHANNEL UPSWITCHINGIf UE is not Idle, Channel == FACH and BufferLevel > 512

bytes:

Channel = DCH and TransmissionRate = 512 kbps;

CHANNEL DOWNSWITCHING

If UE is not Idle, Channel == DCH and Emptytime > 3 seconds:

Channel = FACH: TransmissionRate = 16 kbps;

SERVICE-DEPENDENT CHANNEL UPSWITCHING ON QoS

If UE is not Idle and Service is Streaming/Interactive and

TransmissionTime > MaxAccDelay:TransmissionRate = BufferLevel/MaxAccDelay

where, MaxAccDelay is the maximum acceptable packet delay

caused in the network and acceptable for the user and it

differs for different services. It takes the value of 1

second for streaming and 400 milliseconds for interactive

according to [13] on QoS requirements.

If 512 kbps < TransmissionRate < 1 Mbps:

TransmissionRate = 1 Mbps;

else

TransmissionRate = 2 Mbps.

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Figure 5.1: Calculation of different parameters of the buffer model

As shown in Figure 5.1, if there is an arrival of packet, it will fill thebuffer and gradually the buffer level decreases according to the rate oftransmission through the channel allocated during that particular state ofUE. These buffer levels are important to understand, how different servicesremain in the RNC buffer, given the transmission rates and switchingconditions according to our model. Furthermore, some of the services maycause the buffer levels to increment quickly due to large burst sizes,

whereas other services may show low levels due to smaller burst sizes.

Moreover, there may be empty times, during which there are no data inthe buffer and it is measured during DCH transmission only, since theresource allocated during dedicated channel transmission is relatively highand needs optimisation also. On the other hand, FACH transmission isshared and it has low bit-rates and less resource allocation, since manyusers share the channel simultaneously.

In addition, the packet buffering delay is measured using the valueobtained as the difference between the time of arrival of packet in buffer

and time of the packet leaving the buffer totally.

This packet buffering delay is an important factor because, the buffershould not take longer time to process the packets, since the end-to-endpacket delays should be within the acceptable limit for delay-sensitiveservices. This has been used for validation of the model and the resultswill be explained in Section 5.4.

In addition, the user throughput is also calculated for different services,

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depending on the channel bit-rate at the moment of packet arrival. The

time at which the packet is fully serviced is calculated as follows:

tpd

= tp1d

+ tps (5.1)

where,tpd

- Epoch time stamp of the complete packet departure from the buffer, inseconds

tp1d

- Epoch time stamp when the previous packet is serviced (if thepacket arrives at empty buffer, this time is the packet arrival time), inseconds

tps - Time taken to service the packet fully, in seconds

The time taken to service a packet is calculated from the followingformula,

tps =

Sp

BCH(5.2)

where,Sp - Packet Size, in bits

B

CH

- Transmission bit-rate depending on the transport channel allocated,in bps.

5.3 Transport Channels and State Transitions

As mentioned in the Section 2.1.3, the transport channels such as DCHand FACH are allocated by the RNC, to attain data transmission accordingto the data in buffer. As can be seen from the Figure 5.3, there are two modesof operations according to the activity of data transmission through differenttransport channels and the channel switching is dependent on parameterssuch as

Up-switch Threshold

Down-switch Timer

Inactivity Timer

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made.

Moreover the down-switching to FACH from DCH is caused due toexpiry of the down-switching timer, which has 3 seconds as default timervalue in this study. The down-switching from DCH to FACH is consideredto happen after 3 seconds, since longer duration than this value on DCHcould lead to radio resource waste and shorter may lead to excessiveup-switch after premature down-switch i.e. frequent switching.

The UE is considered to be Idle mode, if there are no packet arrivalsfor 300 seconds, which is considered as the termination of the session.

5.4 Effects of Buffering Delays and QoS

Even though there are default link bit-rates, the delays due to bufferingfor delay-sensitive services should be analysed in order to conform thebuffer model with acceptable QoS packet delays for different services.

Moreover, this is evaluated in order to demonstrate the validity of themodel, by comparing the packet delays due to RAN buffering and RANtransmission with the end-to-end QoS delay for different services. Thefollowing Table 5.1 gives the acceptable overall end-to-end packet delayrange for different services according to ITU-T and 3GPP QoS Standards.

Table 5.1: QoS End-to-End Packet Delay Range for Different Services [13]

Resource Type TrafficClass

AcceptableDelay

Services

GBR Streaming 1 s Non-ConversationalVideo, Audio, Media(Buffered Streaming)

Non-GBR Interactive 400 ms Interactive Gaming, TCPbased (instant-messaging,social-networking, web-browsing, maps)

Non-GBR Background Best Effort TCP-based (email,filesharing, p2p, file-download, software-update, advertisement)

The buffer model includes the aforementioned QoS requirements, byincrementing the transmission rates up to 2 Mbps if packet buffering delayis more than the QoS delay and this avoids additional delay.

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The packet delay due to buffering is calculated using the following formula,

Bp = (tp

d t

pa) 1000 (5.3)

where,Bp - Packet buffering delay, in milliseconds

tpd

- Epoch time stamp when the packet is fully serviced (both waiting andservice), in seconds

tpa - Epoch time stamp when the packet arrives at the buffer, in seconds

With the help of the above formula, the average packet delay due tobuffering for the modelled RNC buffer is calculated for different services.

As shown in the Figure 5.4, almost all the services show packet delaysdue to buffering within the acceptable QoS packet delay budget as shownin Table 5.1, leading to conformance of the valid buffer model havingdefault 512 Kbps DCH, which can go higher upto 2 Mbps if there is a needto send the packets within the acceptable delays and default 16 KbpsFACH, which cannot be varied.

advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 5 10 15 20 25 30 35

Services

Packet Delay on Buffering [milliseconds]

Average Packet Delay due to Buffering

Figure 5.4: Average Buffering Delays for different services

It is also evident from Figure 5.4 that, all the services are found tohave low delays due to buffering at RNC around 20 ms.

In addition, the services such as file-download and software-update

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showing larger burst sizes in Figure 4.8, are found to have longer delays,

which is also considered to ensure the validity of the buffer model.

5.5 Attained Buffer Levels

In addition to the above analysis, it is important to analyse the bufferlevels achieved, due to varying play-out rates. Furthermore, the bufferlevels can be higher for services which need high bandwidth, and also dueto larger bursts and relatively low play-out rates.

Furthermore, these variations have an impact on buffer levels fordifferent services due to this type of link allocation procedure and the

following Figure 5.5 shows the variation in buffer levels during downlinkdata transmission for different services.

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Figure 5.5: Buffer filling levels for different services

From the Figure 5.5, it is evident that around 80% of the buffer levelsfor GBR streaming services except media-playback is between 1 kB and1 MB.

Similarly in case of non-GBR interactive services such as web-browsingand maps around 90% of the buffer levels are in the same range as that ofstreaming services.

Conversely, non-GBR interactive services such as gaming,

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The RNC buffer modelled has no maximum limit and considered to

be of a leaky-bucket model having random rate of packet arrivals anddeterministic play-out rates with default setting of 512 Kbps throughDCH and 16 Kbps through FACH. However, in case of delay-sensitiveservices, the rates can be incremented upto 2 Mbps, when transmissionis through DCH. This is performed by tracking the buffer levels andtransmission time taken to service the packets arrived at the buffer fordifferent services.

From the observations made after supplying the obtained traffic dataas input to the modelled buffer, it is evident that all the services incurpacket delays at RAN lower than the acceptable limit according to

end-to-end QoS packet delay budget set for 3G and LTE network fordifferent services [13], indicating the validity of the buffer model forthe study involved.

The buffer levels achieved by different services are comparatively highin case of non-GBR background services such as email, file-downloadand software-update in increasing order.

The buffer levels are estimated to understand the validity of the resultswith the help of input data. It is observed that services having largebursts as shown in Figure 4.8 are found to have higher buffer levels asshown in Figure 5.5 than other services and this is considered to be a

validation check for the buffer model and the results obtained.

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down-switching happens. This value is an assumption, which is found to

be valid in most of the networks.

Due to varying characteristics of data services in 3G networks, for somedata services, during DCH transmission, there may be empty times inbuffer, making the resources occupied by the user but no data transmissionduring those periods.

The second research question is addressed in this section, by analysingthe emptiness of buffer during DCH transmission for different services andthe percentage of empty buffer duration observed from the total DCHsession duration.

6.1.1 Empty Buffer Duration [De]

In this section, the variations in the empty buffer times for differentservices are analysed, during which no data is present in the buffer duringDCH transmission, but the radio resources allocated for the user are stilloccupied. This value is calculated using,

De = tds tbe (6.1)

where,De - Empty Buffer Duration in seconds

tds - Epoch time when down-switching occurs from DCH to FACH duringeach DCH session

tbe - Epoch time when buffer becomes empty during DCH session

As shown in the following Figure 6.1, most of the services have idlebuffer behaviour for roughly 200 milliseconds duration, which can bemaximum up to 3 seconds as can be seen in some cases, after which thereis a channel down switching to shared channel FACH.

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Figure 6.1: Idle Durations of Buffer during DCH transmission

Furthermore, almost all the services have short empty times less than500 ms in most of the cases. This might be helpful in avoiding frequentdown-switching, but if there are a lot of short empty times, there arepossibilities that the channel may not be used to its full potential.

The following Figure 6.2 shows the average value on empty buffertimes, from which it is clear that almost all the services have a meanempty buffer duration of about 500 milliseconds, a bit higher in case ofgaming, software-update and advertisement reaching roughly around 700

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milliseconds.

advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Services

Average Empty Buffer Time [seconds]

Mean Idle Buffer Time

Figure 6.2: Average Idle Durations of Buffer during DCH transmission

It should be noted that, the channel down-switching happens only whenthe down-switching timer expires. So, most of the services do not show large

number of empty times showing maximum value i.e., 3 seconds. However,in the DCH, there occurs empty duration of around 500 milliseconds, whichis observed in most of the services.

6.1.2 Percentage of Emptiness in Buffer per DCH Session[Pe]

The following calculation is performed for each DCH session by findingthe ratio between the total empty buffer duration and the total DCHsession duration like,

Pe = Dte

DDCH 100 (6.2)

where,Pe - Empty Buffer Percentage per DCH session

Dte - Total empty buffer duration during the DCH session

DDCH - Total time duration of the DCH session

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The following Figure 6.3, gives the percentage of these values for each

service, which shows that, most of the empty buffer percentage values aremore than 80% of the total duration for almost all the services exceptvideo-playback and file-download-Android, because of numerous emptytimes of buffer during a DCH session. However, around 60% and 75% ofthe empty percentage values are below 75% for video-playback andfile-download-Android, respectively.

Figure 6.3: Empty Buffer Percentage during DCH sessions

As shown in Figure 6.4, it is evident that the mean empty buffer

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percentage value is around 90% for most of the services, except

file-download-Android, which only shows about 40% of the DCH sessionwith empty RNC buffer, followed by video-playback showing 60% emptypercentage.

advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messagingmaps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 10 20 30 40 50 60 70 80 90 100

Servic

es

Average Empty Buffer Duration [%]

Mean Idle Buffer Duration per DCH Session

Figure 6.4: Average Empty Buffer Percentage during DCH sessions

It is interesting to observe the empty buffer duration percentage ineach DCH session, because due to intermittent short gaps between arrivals,there occurs more short empty times in the buffer causing high emptybuffer percentage during DCH session for most of the services.

6.2 Radio Resource Utilisation in terms ofDedicated Channel Performance

From the above analyses related to RNC buffer behaviour, it is evidentthat most of the services have short gaps between arrivals less than 500 mscausing empty buffer during most of the DCH sessions.

It should be noted that, it incurs more power, RNC cost and resources,when the DCH channels are occupied and the users are inactive duringtheir DCH session.

This section addresses the third research question, which involvesunderstanding the user throughput and transport channel utilisationduring DCH transmission according to our buffer model assumptions and

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obtained traffic data.

6.2.1 Achieved User Throughput on DCH [Ta]

The throughput achieved per DCH session is termed as userthroughput and the maximum achievable is limited to 2 Mbps because ofradio link bit-rate limitations as described in 3GPP Release 7 [27], whichcan be less than that for pure best effort services. The Ta values are foundusing the equation,

Ta =BDCH

DDCH(6.3)

where,Ta - Achieved User Throughput during the DCH session

BDCH - No. of bits transmitted per DCH session

DDCH - Total duration of the DCH session

It should be noted that, Figure 6.5 has throughput values in Mbps onits x-axis, which can have maximum value of 2 Mbps on DCH.

As can be seen from Figure 6.5, GBR streaming services other thanvideo-playback have throughput values around 128 Kbps, whereasvideo-playback is found to have around 60% of the throughput between128 kbps and 1 Mbps.

On the other hand, non-GBR interactive services show throughputvalues less than 64 Kbps during most of the DCH sessions, which is similarto almost all the non-GBR background services. However,file-download-Android show higher throughput values than any otherservices, with roughly around 60% of the DCH sessions with maximum 512kbps throughput.

It should also be noted that, the maximum channel bit-rate is 512 kbpsin case of non-GBR background services, whereas it can be switched up to1 Mbps or 2 Mbps, when the transmission time for a packet to be fullyserviced is more than the acceptable QoS delay for different services asshown in Table 5.1. This is evident from the Figure 6.5.

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Figure 6.5: Achieved Throughput on DCH transmission

The following Figure 6.6 shows that most of the services other thanGBR streaming and file-download-Android services, have an average userthroughput less than 128 kbps.

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advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 0.1 0.2 0.3 0.4 0.5 0.6

Services

Average User Throughput on DCH [Mbps]

Mean Achieved Throughput on DCH

Figure 6.6: Average Achieved Throughput on DCH transmission

6.2.2 Dedicated Channel Utilisation [UDCH]

In addition to the analysis related to the user throughput in theprevious Section 6.2.1, there is a need to evaluate the channel utilisation

by finding the ratio between the achieved and achievable throughput of thededicated channel, which is also termed as DCH utilisation. It can befound using,

UDCH =Ta

TL 100 (6.4)

where,UDCH - Utilisation of the dedicated channel per DCH session

Ta - Achieved user throughput per DCH session

TL - Link throughput achievable or maximum on DCH link during theDCH session

From the following Figure 6.7, it is evident that 35% DCH utilisation isfound in case of 70% GBR streaming services and only 15% DCHutilisation is observed in case of 70% non-GBR interactive services.

Similar characteristics is observed in almost all the non-GBRbackground services which shows around 10% DCH utilisation, except

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advertisement

audio-playback

email

file-download-.*-Android-Market-Android-Market

file-download-.*-iTunes-iTunes

file-sharing

gaming

instant-messaging

maps

media-playback

social-networking

software-update

video-playback

web-browsing

YouTube

0 20 40 60 80 100

Services

Average DCH Utilisation [%]

Mean Utilisation of DCH

Figure 6.8: Average Utilisation of Dedicated Channel for different services

This is a matter of concern, when it comes to resource optimisation inthe radio networks in terms of DCH channel allocation. Furthermore, theaverage utilisation levels of DCH for different services from the Figure 6.8also show that most of the services, except file-download-Android and

video-playback show average DCH utilisation less than 20%.

6.3 Discussion of the Results

From the statistical analysis with the obtained real network traces andtheir behaviour from the buffer model, the following results are implied:

For almost all the services, the burst size and duration depend on thetype and content abundance of the particular service. Longerdurations of bursts are seen in advertisement and software-update

services and larger bursts are found in most of the GBR streaming,file-download and software-update services.

Short empty buffer times are observed during DCH sessions fordifferent services and most of their values are below 500 milliseconds,but the percentage of total empty time duration to a DCH sessionduration is around 80% for most of the services.

The user throughput values are found to have significantly lowervalues than the achievable throughput of the channel and in turn theDCH utilisation is also found to achieve lower values for most of the

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services, which is suboptimal when it comes to effective radio

resource utilisation.

6.4 Validity of the Results

As a general idea, a methodology to study the RNC buffer characteristicsand DCH channel utilisation has been proposed, which persuaded us toconclude that there exists undesirable resource utilisation with respect totransport channel allocation and overall performance of different services.

Bit-Rate Assumptions

It should be noted that the results are valid only for the conditionsassumed in terms of bit-rate conditions in the DCH and FACHchannels.

In order to avoid congestion at the RAN, the mobile operatorshave to consider a fair network policy control framework. Thisdiffers from one operator to another, since the priorities mightvary for the services among different operators. In addition, itmay be the time-sensitive data getting higher priority than thenon-time-sensitive data or delivery of normal users data moreimportant than the heavy users data or the service for providingfor premium subscribers data might be more important than the

basic subscribers data. However, the bit-rates exhibited in the real network during