WILEY Beyond 3G User Manual
Beyond 3G – Bringing
Networks, Terminals and
the Web Together
Beyond3G–BringingNetworks,TerminalsandtheWebTogether:LTE, WiMAX, IMS, 4G Devices and the Mobile Web 2.0
MartinSauter © 2009JohnWiley&Sons,Ltd. ISBN: 978-0-470-75188-6
Beyond 3G – Bringing
Networks, Terminals
and the Web Together
LTE, WiMAX, IMS, 4G Devices and
the Mobile Web 2.0
Martin Sauter
Nortel, Germany
A John Wiley and Sons, Ltd, Publication
This edition first published 2009
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Library of Congress Cataloging-in-Publication Data
Sauter, Martin.
Beyond 3G : bringing networks, terminals and the Web together / Martin Sauter.
p. cm.
Includes bibliographical references and index.
ISBN 978-0-470-75188-6 (cloth)
1. Wireless Internet. 2. Smartphones. 3. Mobile computing. I. Title.
TK5103.4885.S38 2009
621.382—dc22
A catalogue record for this book is available from the British Library.
ISBN 978-0-470-75188-6 (H/B)
Set in 10/12pt Times by Integra Software Services Pvt. Ltd. Pondicherry, India
Printed and bound in Great Britain by Antony Rowe Ltd.
2008047071
Contents
Preface xi
1 Evolution from 2G over 3G to 4G 1
1.1 First Half of the 1990s – Voice-centric Communication 1
1.2 Between 1995 and 2000: the Rise of Mobility and the Internet 2
1.3 Between 2000 and 2005: Dot Com Burst, Web 2.0, Mobile Internet 2
1.4 From 2005 to today: Global Coverage, VoIP and Mobile Broadband 4
1.5 The Future – the Need for Beyond 3G Systems 5
1.6 All Over IP 8
1.7 Summary 11
References 11
2 Beyond 3G Network Architectures 13
2.1 Overview 13
2.2 UMTS, HSPA and HSPAþ 14
2.2.1 Introduction 14
2.2.2 Network Architecture 14
2.2.3 Air Interface and Radi o Network 23
2.2.4 HSPA (HSDPA and HSUPA) 31
2.2.5 HSPAþ and other Improvements: Competition for LTE 36
2.3 LTE 45
2.3.1 Introduction 45
2.3.2 Network Architecture 46
2.3.3 Air Interface and Radi o Network 51
2.3.4 Basic Procedures 65
2.3.5 Summary and Comparison with HSPA 68
2.3.6 LTE-Advanced 69
2.4 802.16 WiMAX 70
2.4.1 Intr oduction 70
2.4.2 Net work Architecture 70
vi Contents
2.4.3 The 802.16d Air Interface and Radio Network 76
2.4.4 The 802.16e Air Interface and Radio Network 79
2.4.5 Basic Procedures 83
2.4.6 Summ ary and Comparison with HSPA and LTE 85
2.4.7 802.16 m: Complying with IMT-Advanced 86
2.4.8 802.16 j: Mobile Multihop Relay 87
2.5 802.11 Wi-Fi 88
2.5.1 Introduction 88
2.5.2 Network Architecture 89
2.5.3 The Air Interface – from 802.11b to 802.11n 92
2.5.4 Air Interface and Resource Management 97
2.5.5 Basic Procedures 101
2.5.6 Wi-Fi Security 101
2.5.7 Quality of Service: 802.11e 103
2.5.8 Summary 104
References 105
3 Network Capacity and Usage Scenarios 107
3.1 Usage in Developed Markets and Emerging
Economies 107
3.2 How to Control Mobile Usage 108
3.2.1 Per Minute Charging 109
3.2.2 Volume Charging 109
3.2.3 Split Charging 109
3.2.4 Small-screen Flat Rates 109
3.2.5 Strategies to Inform Users When Their Subscribed Data
Volume is Used Up 110
3.2.6 Mobile Internet Access and Prepaid 110
3.3 Measuring Mobile Usage from a Financial Point of View 111
3.4 Cell Capacity in Downlink 112
3.5 Current and Future Frequency Bands for Cellular
Wireless 117
3.6 Cell Capacity in Uplink 118
3.7 Per-user Throughput in Downlink 120
3.8 Per-user Throughput in the Uplink 125
3.9 Traffic Estimation Per User 127
3.10 Overall Wireless Network Capacity 129
3.11 Network Capacity for Train Routes, Highways and Remote Areas 133
3.12 When will GSM be Switched Off? 135
3.13 Cellular Network VoIP Capacity 136
3.14 Wi-Fi VoIP Capacity 140
3.15 Wi-Fi and Interference 141
3.16 Wi-Fi Capacity in Combination with DSL and Fibre 143
3.17 Backhaul for Wireless Networks 148
3.18 A Hybrid Cellular/Wi-Fi Network for the Future 153
References 155
Contents vii
4 Voice over Wireless 157
4.1 Circuit-switched Mobile Voice Telephony 158
4.1.1 Circuit Switching 158
4.1.2 A Voice-optimized Radio Network 159
4.1.3 The Pros of Circuit Switching 159
4.2 Packet-switched Voice Telephony 159
4.2.1 Net work and Applications are Separate in Packet-switched
Networks 160
4.2.2 Wireless Network Architecture for Transporting IP packets 160
4.2.3 Ben efits of Migrating Voice Telephony to IP 162
4.2.4 Voice Telephony Evolution and Service Integration 162
4.2.5 Voice Telephony over IP: the End of the Operator Monopoly 163
4.3 SIP Telephony over Fixed and Wireless Networks 164
4.3.1 SIP Registration 164
4.3.2 Establishing a SIP Call Between Two SIP Subscribers 167
4.3.3 Session Description 169
4.3.4 The Real-time Transfer Protocol 171
4.3.5 Establishing a SIP Call Between a SIP and a PSTN Subscriber 172
4.3.6 Proprietary Components of a SIP System 174
4.3.7 Net work Address Translation and SIP 175
4.4 Voice and Related Applications over IMS 176
4.4.1 IMS Basic Architecture 179
4.4.2 The P-CSCF 181
4.4.3 The S-CSCF and Application Servers 182
4.4.4 The I-CSCF and the HSS 184
4.4.5 Media Resource Functions 186
4.4.6 User Identities, Subscription Profiles and Filter Criteria 188
4.4.7 IMS Registration Process 190
4.4.8 IMS Session Establishment 194
4.4.9 Voice Telephony Interworking with Circuit-switched Networks 199
4.4.10 Push-to-talk, Presence and Instant Messaging 203
4.4.11 Voice Call Continuity 206
4.4.12 IMS with Wireless LAN Hotspots and Private Wi-Fi
Networks 209
4.4.13 IMS and TISPAN 213
4.4.14 IMS on the Mobile Device 216
4.4.15 Challenges for IMS Rollouts 219
4.4.16 Opportunities for IMS Rollouts 222
4.5 Voice over DSL and Cable with Femtocells 224
4.5.1 Femto cells from the Network Operator’s Point of View 226
4.5.2 Femto cells from the User’s Point of View 227
4.5.3 Conc lusion 228
4.6 Unlicensed Mobile Access and Generic Access Network 228
4.6.1 Tec hnical Background 229
4.6.2 Adva ntages, Disadvantages and Pricing Strategies 231
References 232
viii Contents
5 Evolution of Mobile Devices and Operating Systems 235
5.1 Introduction 235
5.1.1 The ARM Architecture 237
5.1.2 The x86 Architecture for Mobile Devices 238
5.1.3 Fro m Hardware to Software 238
5.2 The ARM Architecture for Voice-optimized Devices 238
5.3 The ARM Architecture for Multimedia Devices 241
5.4 The x86 Architecture for Multimedia Devices 244
5.5 Hardware Evolution 247
5.5.1 Chipset 247
5.5.2 Process Shrinking 248
5.5.3 Displays and Batteries 249
5.5.4 Oth er Additional Functionalities 250
5.6 Multimode, Multifrequency Terminals 252
5.7 Wireless Notebook Connectivity 255
5.8 Impact of Hardware Evolution on Future Data Traffic 255
5.9 The Impact of Hardware Evolution on Networks and Applications 257
5.10 Mobile Operating Systems and APIs 258
5.10.1 Java and BREW 258
5.10.2 BREW 259
5.10.3 Symbian/S60 260
5.10.4 Windows Mobile 262
5.10.5 Linux: Maemo, Android and Others 262
5.10.6 Fracturization 265
5.10.7 Operating System Tasks 265
References 271
6 Mobile Web 2.0, Applications and Owners 273
6.1 Overview 273
6.2 (Mobile) Web 1.0 – How Everything Started 274
6.3 Web 2.0 – Empowering the User 275
6.4 Web 2.0 from the User’s Point of View 275
6.4.1 Blogs 276
6.4.2 Media Sharing 277
6.4.3 Pod casting 277
6.4.4 Adva nced Search 277
6.4.5 User Recommendation 278
6.4.6 Wikis – Collective Writing 278
6.4.7 Social Networking Sites 279
6.4.8 Web Applications 280
6.4.9 Ma shups 280
6.4.10 Virtual Worlds 281
6.4.11 Long-tail Economics 281
6.5 The Ideas Behind Web 2.0 282
6.5.1 The Web as a Platform 282
6.5.2 Harne ssing Collective Intelligence 283
Contents ix
6.5.3 Data is the Next Intel Inside 284
6.5.4 End of the Software Release Cycle 284
6.5.5 Lightweight Programming Models 285
6.5.6 Software above the Level of a Single Device 285
6.5.7 Rich User Experience 285
6.6 Discovering the Fabrics of Web 2.0 286
6.6.1 Aggregation 286
6.6.2 AJAX 289
6.6.3 Tag ging and Folksonomy 290
6.6.4 Open Application Programming Interfaces 293
6.6.5 Open Source 295
6.7 Mobile Web 2.0 – Evolution and Revolution of Web 2.0 296
6.7.1 The Seven Principles of Web 2.0 in the Mobile World 296
6.7.2 Adva ntages of Connected Mobile Devices 301
6.7.3 Offline Web Applications 304
6.7.4 The Mobile Web, 2D Barcodes and Image Recognition 308
6.7.5 Wa lled Gardens, Mobile Web 2.0 and the Long Tail 310
6.7.6 Web Page Adaptation for Mobile Devices 311
6.8 (Mobile) Web 2.0 and Privacy 317
6.8.1 On- page Cookies 318
6.8.2 Inter-site Cookies 320
6.8.3 Flash Shared Objects 320
6.8.4 Site Information Sharing, Social Distribution 321
6.8.5 Session Tracking 322
6.9 Mobile Applications 322
6.9.1 Web Browsing 323
6.9.2 Audio 324
6.9.3 Media Sharing 328
6.9.4 Video and TV 330
6.9.5 Voice and Video Telephony 332
6.9.6 Widgets 333
6.9.7 Social Media 335
6.9.8 Microblogging 335
6.9.9 Loc ation 338
6.9.10 Shopping 340
6.9.11 Mobile Web Servers 341
References 343
7 Conclusion 345
Index 349
Preface
In recent years, cellular voice networks have transformed into powerful packet-switched
access networks for both voice communication and Internet access. Current 3.5G networks such as UMTS/HSDPA and CDMA 1xEvDO now deliver bandwidths of several
megabits per second to individual users, and mobile access to the Internet from handheld
devices and notebooks is no longer perceived as slower than a DSL or cable connection.
Bandwidth and capacity demands, however, keep rising because of the increasing number of people using the networks and due to new bandwidth-intensive applications such
as video streaming and mobile Internet access from notebooks. Thus, network manufacturers and network operators need to find ways to increase capacity and performance
while reducing cost.
In the past, network evolution mainly involved designing access networks with more
bandwidth and capacity. As we go beyond 3G network architectures, there is now also an
accelerated evolution of core networks and, most importantly, user devices and applications. This evolution follows the trends that are already in full swing in the ‘fixed-line’
Internet world today. Circuit-switched voice telephony is being replaced by voice over IP
technologies and Web 2.0 has empowered consumers to become creators and to share
their own information with a worldwide audience. In the future, wireless networks will
have a major impact on this trend, as mobile phones are an ideal tool for creating and
consuming content. The majority of mobile phones today have advanced camera and
video capabilities, and together with fast wireless access technologies, it becomes possible
to share information with others instantly.
While all these trends are already occurring, few resources are available that describe
them from a technical perspective. This book therefore aims to introduce the technology
behind this evolution. Chapter 1 gives an overview of how mobile networks have evolved
in the past and what trends are emerging today. Chapter 2 then takes a look at radio
access technologies such as LTE, HSPA+, WiMAX and the evolution of the Wi-Fi
standard. Despite the many enhancements next-generation radio systems will bring,
bandwidth on the air interface is still the limiting factor. Chapter 3 takes a look at the
performance of next-generation systems in comparison to today’s networks, shows
where the limits are and discusses how Wi-Fi can help to ensure future networks can
meet the rising demand for bandwidth and integrated home networking. Voice over IP is
xii Preface
already widely used in fixed line networks today and ‘Beyond 3G’ networks have enough
capacity and performance to bring about this cha nge in the wireless world as well.
Chapter 4 thus focuses on Voice over IP architectures, such as the IP Multimedia
Subsystem (IMS) and the Session Initiation Protocol (SIP) and discusses the impacts of
these systems on future voice and multimedia communication. Just as important as
wireless networks are the mobile devices using them, and Chapter 5 gives an overview
of current mobile device architectures and their evolution. Finally, mobile devices are
only as useful as the applications running on them. So Chapt er 6 discusses how ‘mobile
Web 2.0’ applications will change the way we communicate in the future.
No book is written in isolation and many of the ideas that have gone into this manuscript are the result of countless conversations over the years with people from all across
the industry. Specifically, I would like to thank Debby Maxwell, Prashant John, Kevin
Wriston, Peter van den Broek and John Edwards for the many insights they have provided
to me over the years in their areas of expertise and for their generous help with reviewing
the manuscript. A special thank-you goes to Berenike for her love, her passion for life and
for inspiring me to always go one step further. And last but not least I would like to thank
Mark Hammond, Sarah Tilley, Sarah Hinton and Katharine Unwin of John Wiley and
Sons for the invaluable advice they gave me throughout this project.
1
Evolution from 2G over 3G to 4G
In the past 15 years, fixed line and wireless telecommunication as well as the Internet have
developed both very quickly and very slowly depending on how one looks at the domain.
To set current and future developments into perspective, the first chapter of this book
gives a short overview of major events that have sh aped these three sectors in the previous
one-and-a-half decades. While the majority of the developm ents described below took
place in most high-tech countries, local factors and national regulation delayed or
accelerated events. Therefore, the time frame is split up into a number of periods and
specific dates are only given for country-specific examples.
1.1 First Half of the 1990s – Voice-centric Communication
Fifteen years ago, in 1993, Internet access was not widespread and most users were either
studying or working at universities or in a few select companies in the IT industry. At this
time, whole universities were connected to the Internet with a data rate of 9.6 kbit/s.
Users had computers at home but dial-up to the university network was not yet widely
used. Distributed bulletin board networks such as the Fidonet [1] were in widespread use
by the few people who were online then.
It can therefore be said that telecommunication 15 years ago was mainly voice-centric
from a mass market point of view. An online telecom news magazine [2] gives a number of
interesting figures on pricing around that time, when the telecom monopolies where still
in place in most European countries. A 10 min ‘long-distance’ call in Germany during
office hours, for example, cost E3.25.
On the wireless side, first-generation analog networks had been in place for a
number of years, but their use was even more expensive and mobile devices were
bulky and unaffordable except for business users. In 1992, GSM networks had been
launched in a number of European countries, but only few people noticed the launch
of these networks.
Beyond3G–BringingNetworks,TerminalsandtheWebTogether:LTE, WiMAX, IMS, 4G Devices and the Mobile Web 2.0
MartinSauter © 2009JohnWiley&Sons,Ltd. ISBN: 978-0-470-75188-6
2 Beyond 3G – Bringing Networks, Terminals and the Web Together
1.2 Between 1995 and 2000: the Rise of Mobility and the Internet
Around 1998, telecom monopolies came to an end in many countries in Europe. At the
time, many alternative operators were preparing themselves for the end of the monopoly
and prices went down significantly in the first weeks and months after the new regulation
came into effect. As a result, the cost of the 10 min long-distance call quickly fell to only a
fraction of the former price. This trend continues today and the current price is in the
range of a few cents. Also, European and even intercontinental phone calls to many
countries, like the USA and other industrialized countries, can be made at a similar cost.
At around the same time, another important milestone was reached. About 5 years
after the start of GSM mobile networks, tariffs for mobile phone calls and mobile phone
prices had reached a level that stimulated mass market adoption. While the use of a
mobile phone was perceived as a luxury and mainly for business purposes in the first
years of GSM, adoption quickly accelerated at the end of the decade and the mobile
phone was quickly transformed from a high-price business device to an indispensable
communication tool for most people.
Fixed line modem technology had also evolved somewhat during that time, and
modems with speeds of 30–56 kbit/s were slowly being adopted by students and other
computer users for Internet access either via the university or via private Internet dial-up
service providers. Around this time, text-based communication also started to evolve and
Web browsers appeared that could show Web pages with graphic al content. Also, e-mail
leapt beyond its educational origin. Content on the Internet at the time was mostly
published by big news and IT organizations and was very much a top-down distribution
model, with the user mainly being a consumer of information. Today, this model is
known as Web 1.0.
While voice calls over mobile networks quickly became a success, mobile Internet
access was still in its infancy. At the time, GSM networks allowed data rates of 9.6 and
14.4 kbit/s over circuit-switched connections. Few people at the time made use of mobile
data, however, mainly due to high costs and missing applications and devices.
Nevertheless, the end of the decade saw the first mobile data applications such as Web
browsers and mobile e-mail on devices such as Personal Digital Assistants (PDAs), which
could communicate with mobile phones via an infrared port.
1.3 Between 2000 and 2005: Dot Com Burst, Web 2.0, Mobile Internet
Developments continued and even accelerated in all three sectors despite the dot com
burst in 2001, which sent both the telecoms and the Internet industry into a downward
spiral for severa l years. Despite this downturn, a number of new important developments
took place during this period.
One of the major breakthroughs during this period was the rise of Internet access
via Digital Subscriber Lines (DSL) and TV cable modems. These quickly replaced
dial-up connections as they became affordable and offered speeds of 1 MBit/s and
higher. Compared with the 56 kbit/s analog modem connections, the download times
for web pages with graphical content and larger files improved significantly. At the
end of this period, the majority of people in many countries had access to broadband
Internet that allowed them to view more and more complex Web pages. Also, new
Evolution from 2G over 3G to 4G 3
forms of communication like Blogs and Wikis appeared, which quickly revolutionized the creator–consumer imbalance. Suddenly, users were no longer only consumers of content, but could also be creators for a worldwide audience. This is one of
the main propert ies of what is popularly called Web 2.0 and will be further discussed
later on in this book.
In the fixed line telephony world, prices for national and international calls continued
to decline. Towards the end of this period, initial attempts were also made to use
the Internet for transporting voice calls. Early adopters discovered the use of
Internet telephony to make phone calls over the Internet via their DSL lines.
Proprietary programs like Skype suddenly allowed users to call any Skype subscriber
in the world for free, in many cases with superior voice quality. ‘Free’ in this regard is a
relative term, however, since both parties in the call have to pay for access to the Internet,
so telecom operators still benefit from such calls due to the monthly charge for DSL or
cable connections. Additionally, many startup companies started to offer analog telephone to Internet Protocol (IP) telephone converters, which used the standardized SIP
(Session Initiation Protocol) protocol to transport phone calls over the Internet.
Gateways ensured that such subscribers could be reached via an ordinary fixed line
telephone number and could call any legacy analog phone in the world. Alternative
long-distance carriers also made active use of the Internet to tunnel phone calls between
countries and thus offer cheaper rates.
Starting in 2001, the General Packet Radio Service (GPRS) was introduced in public
GSM networks for the first time. When the first GPRS-capable mobile phones quickly
followed, mobile Internet access became practically feasible for a wider audience. Until
then, mobile Internet access had only been possible via circuit-switched data calls.
However, the data rate, call establishment times and the necessity of maintaining the
channel even during times of inactivity were not suitable for most Internet applications.
These problems, along with the small and monochrome displays in mobile phones and
mobile software being in its infancy, meant that the first wireless Internet services
(WAP 1.0) never became popular. Towards 2005, devices matured, high-resolution
color displays made it into the mid-range mobile phone segment and WAP 2.0 mobile
Web browsers and easy-to-use mobile e-mail clients in combination with GPRS as a
packet-switched transport layer finally allowed mobile Internet access to cross the threshold between niche and mass market. Despite these advances, pricing levels and the
struggle between open and closed Internet gardens, which will be discussed in more detail
later on, slowed down progress considerably.
At this point it should be noted that throughout this book the terms ‘mobile access to
the Internet’ and ‘mobile Internet access’ are used rather than ‘mobile Internet’. This is
done on purpose since the latter term implies that there might be a fracture between a
‘fixed line’ and a ‘mobile’ Internet. While it is true that some services are specifically
tailored for use on mobile devices and even benefit and make use of the user’s mobility,
there is a clear trend for the same applications, services and content to be offered and
useful on both small mobile devices and bigger nomadic or stationary devices. This will
be discussed further in Chapter 6.
Another important milestone for wireless Internet access during this timeframe was 3G
networks going online in many countries in 2004 and 2005. While GPRS came close to
analog modem speeds, UMTS brought data rates of up to 384 kbit/s in practice, and the
4 Beyond 3G – Bringing Networks, Terminals and the Web Together
experience became similar to DSL. Again, network operator pricing held up mass
adoption for several years.
1.4 From 2005 to today: Global Coverage, VoIP and Mobile Broadband
From 2005 to today, the percentage of people in industrialized countries accessing the
Internet via broadband DSL or cable connections has continued to rise. Additionally,
many network operators have started to roll out ADSL2+, and new modems enable
download speeds beyond 15 Mbit/s for users living close to a central exchange. VDSL
and fiber to the curb/fiber to the home deployments offer even higher data rates. Another
trend that has accelerated since 2005 is Voice over IP (VoIP) via a telephone port in the
DSL or cable modem router. This effectively circumvents the traditional analog telephone network and traditional network fixed line telephony operators see a steady
decline in their customer base.
At the time of publication, the number of mobile phone users has reached 3 billion.
This means that almost every second person on Earth now owns a mobile phone, a trend
which only a few people foresaw only five years ago. In 2007, network operators
registered 1000 new users per minute [3]. Most of this growth has been driven by the
rollout of second-generation GSM/GPRS networks in emerging markets. Due to global
competition between network vendors, network components reached a price that made it
feasible to operate wireless networks in countries with very low revenue per user per
month. Another important factor for this rapid growth was ultra-low-cost GSM mobile
phones, which became available for less than $50. In only a few years, mobile networks
have changed working patterns and access to information for small entrepreneurs like
taxi drivers and tradesmen in emerging markets [4]. GSM networks are now available in
most parts of the world. Detailed local and global maps of network deployments can be
found in [5].
In industrialized countries, third-gener ation networks continued to evolve and 2006
saw the first upgrades of UMTS networks to High Speed Data Packet Access (HSDPA).
In a first step, this allowed user data speeds between 1 and 3 Mbit/s. With advanced
mobile terminals, speeds are likely to increase further. Today, such high data rates are
mainly useful in combination with notebooks to give users broadband Internet almost
anywhere. In the mid term, it is likely that HSDPA will also be very beneficial for mobile
applications once podcasts , music downloads and video streaming on mobile devices
become mass market applications.
While 3G networks have been available for some time, take-up was sluggish until
around 2006/2007, when mobile network operators finally introduced attractive price
plans. Prices fell below E40–E50 for wireless broadband Internet access and monthly
transfer volumes of around 5 Gbytes. This is more than enough for everything but file
sharing and substantial video streaming. Operators have also started to offer smaller
packages in the range of E6–15 a month for occasional Internet access with notebooks.
Packages in a similar price range are now also offered for unlimited Web browsing and
e-mail on mobile phones. Pricing and availability today still vary in different countries.
In 2006, mobile data revenue in the USA alone reached a $15.7 billion, of which 50–60%
is non-SMS revenue [6]. In some countries, mobile data revenues now accounts for
between 20 and 30% of the total operator revenue, as shown in Figure 1.1.
Evolution from 2G over 3G to 4G 5
35
30
25
20
15
10
5
0
T-MobileUSChina
Unicom
Figure 1.1 Percentage of data revenue of mobile operators in 2007 [6].
Vodafone
Ger
O2 UK3 Italy
%
While wireless data roaming is still in its infancy, wireless Internet access via prepaid SIM
cards is already offered in many countries at similar prices to those for customers with a
monthly bill. This is another important step, as it opens the door to anytime and
anywhere Internet access for creative people such as students, who favor prepaid SIMs
to monthly bills. In addition, it makes life much easier for travelers, who until recently
had no access to the Internet while traveling, except for wireless hotspots at airports and
hotels. An updated list of such offers is maintained by the Web community on the prepaid
wireless Internet access Wiki [7].
1.5 The Future – the Need for Beyond 3G Systems
When looking into the future, the main question for network operators and vendors is
when and why Beyond 3G wireless networks will be needed. Looking back only a couple
of years, voice telephony was the first application that was mobilized. The Short Message
Service (SMS) followed some years later as the first mass market mobile data application.
By today’s standards comparably simple mobile phones were required for the service and
little bandwidth. In a way, the SMS service was a forerunner of other data services like
mobile e-mail, mobile Web browsing, mobile blogging, push-to-talk, mobile instant
messaging and many others. Such applications became feasible with the introduction
of packet-based wireless networks that could carry IP data packets and increasingly
powerful mobile devices. Today, the capacity of current 3G and 3.5G netw orks is still
sufficient for the bandwidth requirements of these applications and the number of users.
There are a number of trends, however, which are already visible and will increase
bandwidth requirements in the future:
Rising use – due to falling prices, more people will use mobile applications that require
network access.
Multimedia content – while first attempts at mobilizing the Web resulted in mostly
text-based Web pages, graphical content is now the norm rather than the exception.
6 Beyond 3G – Bringing Networks, Terminals and the Web Together
A picture may paint a thousand words, but it also increases the amount of data that has
to be transferred for a Web page. Video and music downloads are also becoming more
popular, which further increases in bandwidth requirements.
Mobile social networks – similar to the fixed-line Internet, a different breed of
applications is changing the way people are using the Internet. In the past, users
mainly consumed content. Blogs, podcasts, picture-sharing sites and video portals
are now reshaping the Internet, as users no longer only consume content, but use the
network to share their own ideas, pictures and videos with other people. Applications
like, for example, Shozu [8] and Lifeblog [9] let users upload pictures, videos and Blog
entries from mobile devices to the Web. In particular, picture, podcast and video
transfers multiply the amount of data that users transmit and receive.
Voice over IP – the fixed line world is rapidly moving towards VoIP. It is likely that,
five years from now, many of today’s fixed line circuit-switched voice networks will
have migrated towards IP-based voice transmission. Likewise, on the network access
side, many users will use VoIP as their primary fixed line voice service, for example
over DSL or TV cable networks. The beginnings can already been observed today, as
the circuit-switched voice market is under increasing pressure due to declining subscriber numbers. As a consequence, many operators are no longer investing in this
technology. A similar trend can be observed in wireless networks. Here, however, the
migration is much slower, especially due to the higher bandwidth requirements for
transporting voice calls over a packet-switched bearer. This topic is discussed in more
detail in Chapter 1.6.
Fixed-line Internet replacement – while the number of voice minutes is increasing,
revenue is declining in both fixed line and the wireless networks due to falling prices. In
many countries, wireless operators are thus trying to keep or increase the average
revenue per user by offering Internet access for PCs, notebooks and mobile devices
over their UMTS/HSDPA or CDMA networks. Thus, they have started to compete
directly with DSL and cable operators. Again, this requires an order of magnitude of
additional bandwidth on the air interface.
Competition from alternative wireless Internet providers – in some co untries, alternative operators are already offering wireless broadband Internet access with Wi-Fi or
WiMAX/802.16 networks. Such operators directly compete with traditional UMTS
and CDMA carriers, who are also active in this market.
The broadband Internet is not a socket in the wall – this statement combines all
previous arguments and was made by Anssi Vanjoki, Executive VP of Nokia’s
Multimedia division [10], at a press conference. Today, many people already use WiFi access points to create their personal broadband Internet bubble. Thus, broadband
Internet is virtually all around them. In the future, people will not only use this bubble
with desktop computers and notebooks, but also with smaller devices such as mobile
phones with built-in Wi-Fi capabilities. Smaller devices will also change the way we
perceive this Internet bubble. No longer is it necessary to sit down at a specific place,
for example in front of a computer, in order to communicate (VoIP, e-mail, instant
messaging), to get information or to publish information to the Web (pictures, Blog
entries, videos, etc.). When the personal broadband bubble is left, mobile devices
switch over to a cellular network. As we move into the future, the cellular network
will extend into areas not covered today and available bandwidth will have to increase
Evolution from 2G over 3G to 4G 7
to cope with the rising number of users and their connected applications. Moving
between the personal Internet bubble at home and the larger external cellular network
will become seamless as devices and services evolve.
A number of wireless technologies are currently under development or in the early
rollout phase that are designed to meet these future demands: 3GPP’s Long Term
Evolution (LTE), HSPA+ and WiMAX. In addition, Wi-Fi is also likely to be an
important network technology that is required to meet future capacity demands. All of
these technologies will be further discussed in Chapter 2. The question that arises in this
context is which of these technologies are 3G and which will be called 4G in the future?
The body responsible for categorizing wireless networks is the International
Telecommunication Union (ITU). The ITU categorizes International Mobile
Telecommunication (IMT) networks as follows:
IMT-2000 systems – this is what we know as 3G systems today, for example UMTS
and cdma2000. The list of all ITU-2000 systems is given in ITU-R M.1457-6 [11].
Enhanced IMT-2000 systems – the evolution of IMT-2000 systems, for example
HSPA, CDMA 1xEvDo and future evolutions of these systems.
IMT-Advanced systems – systems in this category are considered to be 4G systems.
At this time, there is still no clear definition of the characteristics of future IMTAdvanced (4G) systems. The ITU-R M.1645 recommendation [12] gives first hints but
leaves the door wide open:
It is predicted that potential new radio interface(s) will need to support data rates of up to
approximately 100 Mbit/s for high mobility such as mobile access and up to approximately
1 Gbit/s for low mobility such as nomadic/local wireless access, by around the year 2010 [...]
These data rate figures and the relationship to the degree of mobility [...] should be seen as
targets for research and investigation of the basic technologies necessary to implement the
framework. Future system specifications and designs will be based on the results of the research
and investigations.
When comparing current the WiMAX specifications to these potential requirements, it
becomes clear that WiMAX does not qualify as a 4G IMT-Advanced standard, since
data rates are much lower, even under ideal conditions.
3GPP’s successor to its 3G UMTS standard, known as LTE, will also have difficulties
fulfilling these requirements. Even with a four-way Multiple Input Multiple Output
(MIMO) transmission, data rates in a 20 MHz carrier would not exceed 326 Mbit/s. It
should be noted at this point that this number is already a long stretch, since putting four
antennas in a small device or on a rooftop will be far from simple in practice.
It is also interesting to compare these new systems with the evolution of current 3G
systems. The evolution of UMTS is a good example. With HSDPA and HSUPA, user
speeds now exceed the 2 Mbit/s that was initially foreseen for IMT-2000 systems. The
evolution of those systems, however, has not yet come to an end. Recent new developments in 3GPP Release 7 and 8 called HSPA+, which include MIMO technology and
other enhancements, bring ev olved UMTS technology to the same capacity and
8 Beyond 3G – Bringing Networks, Terminals and the Web Together
bandwidth levels as currently specified for LTE on a 5 MHz carrier. HSPA+ is also
clearly not a 4G IMT-Advanced system, since it enhances a current 3G IMT-2000 radio
technology. Thus, HSPA+ is categorized as an ‘enhanced IMT-2000 system’.
To meet the likely requirements of IMT-Advanced, the WiMAX and LTE standards
bodies have started initiatives to further enhance their technologies. On the WiMAX side,
the 802.16m task group is working on standardizing an even faster radio interface. On the
LTE side, a similar working program has become known as LTE+ or Enhanced LTE.
Current research indicates that the transmission speed requirements described in
ITU-R M.1645 can only be achieved in a frequency band of 100 MHz or more. This is
quite a challenge, both from a technical point of view and also due to a lack of available
additional spectrum. Thus, it is somewhat doubtful whether these requirements will
remain in place for the final definition of 4G IMT-Advanced.
In practice, several different network technologies will coexist and evolve in the future
to meet the rising demands in terms of bandwidth and capacity. It is also likely that a
combination of different radio systems, like for example LTE together with Wireless
LAN, will be used to satisfy capacity demands.
From a user and service point of view, it does not matter if a network technology is
considered 3.5G, 3.9G or 4G. Thus, this book uses the term ‘Beyond 3G systems’ (B3G),
which includes all technologies which will be able to satisfy future capacity demands and
which either evolve out of current systems or are a new development.
1.6 All Over IP
While on the radio network side it is difficult to foresee which mix of evolved 3G and 4G
technologies will be used in the future, the future of fixed and mobile core networks is
much easier to predict. One of the main characteristics of 3G networks is the support for
circuit-switched and packet-switched services. The circuit-switched part of the core network and circuit-switched services of the radio network were specifically designed to
carry voice and video calls. Service control rests with the Mobile Switching Center
(MSC), the main component of a circuit-switched network. As subscribers can roam
freely in a mobile network, a database is required to keep track of the current location of
the subscriber in addition to the subscription information. This database is referred to as
the Home Location Register (HLR). To establish a call, a mobile phone always contacts
the MSC. The MSC then uses the destination’s telephone number to query the HLR for
the location of the destination subscriber. The call is then routed to this MSC, which in
turn informs the destination subscriber of the incoming call. This process is called
signaling. For the speech path, a transparent circuit-switched channel is established
between the two parties via the MSCs switching matrix. The signaling required for the
call is transferred over an independent signaling network, as the circuit-switched channel
only transports the speech signal.
In recent network designs, MSCs are split into an MSC Call Server component that
handles the signaling and a media gateway that is responsible for forwarding the voice
call as shown in Figure 1.2. Instead of fixed connections, media gateways use packetswitched ATM (Asynchronous Transfer Mode) or IP connections to forward the call.
This removes the necessity to transport the voice data via circuit-switched connections in
the core network.
p
Evolution from 2G over 3G to 4G 9
HLR
Location and Subscriber
Signaling
connection
Database
Call Server
Media
Radio
Network
Radio base station
Figure 1.2 Circuit switching with dedicated network components.
Gateway
Exclusive channel for
a connection or IP data flow
with constant data rate
Call Server
Media
Gateway
Radio
Network
In the radio network ATM or
A circuit switched connections
is used for a call. Voice data
and signaling for the call is not
orted over IP!
trans
While this approach is ideally suited to carry voice and video calls with a constant
bandwidth and delay requirements, it performs poorly for a connection to the Internet.
Here, all data is transported in data packets. Furthermore, data packets are not only
exchanged between two endpoints while a connection is established, but usually between
many. An example is a Web browsing session during which a user visits several Web sites,
sometimes even simultaneously. While a Web page is transferred, it is desirable to use as
much bandwidth as is currently available, rather than be limited to a circuit-switched
channel that is designed to carry a digitized narrowband voice or video stream. An
Internet connection is often also idle for a substantial duration. During this time,
resources are best given to other users. This is also not possible with a circuit-switched
connection, because it is an exclusive channel that offers a fixed amount of bandwidth
between two parties while it is established.
For these reasons, 3G networks contain a separate core network to forward data
packets rather than circuits. This is shown in Figure 1.3. The radio network serves both
the circuit-switched and the packet-switched network and the kind of connection established to a user over the air depends on whether a circuit-switched connection or a packetswitched connection is required. Some systems such as UMTS even allow devices to
simultaneously use packet and circuit connections so a phone call can be made while
being connected to the Internet and transferring data.
Traditional fixed line networks use a similar split for simultaneous voice telephony and
Internet access. Since DSL became popular, analog voice service and DSL use the same
physical line to the customer’s home. A splitter is then used to separat e the analog
telephone signal from the DSL service as they operate in different frequency bands. In
the central exchange office, a similar splitter is used to connect the line of the subscriber to
10 Beyond 3G – Bringing Networks, Terminals and the Web Together
Call Server
Media
Radio
Network
ATM or IP
Figure 1.3 Typical circuit-switched and packet-switched dual architecture of 3G networks. The
location and subscriber database is not shown.
Gateway
Radio Network
Packet Gateway
Call Server
Media
Gateway
Private
IP Network
Radio
Network
Internet
Gateway
Internet
the local circuit-switched exchange for voice calls and additionally to a DSL Access
Multiplexer (DSLAM) for Internet connectivity. Telephone exchanges are then interconnected via circuit-switched connections, while the DSLAM connects to a packetswitched backbone. In the meantime, however, there is a clear shift to transporting
telephone calls over the Internet connection as well. Instead of connecting the analog
phone to the splitter, the DSL access device is equipped with a jack for the phone. The
DSL access device digitizes the voice signal and sends it as IP packets over the DSL
connection. In many cases, an IP-based SIP server and RTP (Real Time Transport
Protocol) replace the local circuit-switched telephone exchange. There are several advantages of this approach:
Only a single type of core network is needed, as the circuit-switched telephone
exchanges and the circuit-switched network between them are no longer
necessary.
Using an IP network for voice calls makes it a lot easier for companies other than the
local telephone carrier to offer telephony services, as the controlling network element
no longer needs to be at the local exchange.
Voice services can be combined with other services. Since there is more bandwidth
available, users can, for example, exchange pictures with each other while being
engaged in a voice call or add video at any point during the conversation.
While the trend to VoIP is already fully underway in fixed-line networks, wireless networks have not yet caught up. Here, things are moving more slowly for a number of
reasons. The main reason is that 3G mobile networks did not have the necessary
bandwidth to support VoIP, which requires a higher data rate than circuit-switched
Evolution from 2G over 3G to 4G 11
voice calls. The gap has been somewhat reduced by the introduction of 3.5G networks.
However, only B3G networks (evolved IMT-2000 and IMT-Advan ced) will have enough
capacity and an optimized radio network to support VoIP on a large scale.
The challenges are significant, but none of the new B3G network architectures discussed
in Chapter 2 have a circuit-switched core network. To be successful, it is essential for B3G
wireless network operators to have a fully functioning VoIP solution in place in the future
that is able to seamlesslytransfer the call to a circuit-switched wireless connection when the
user roams out of network coverage. This is discussed in more detail in Chapter 4.
1.7 Summary
This chapter presented how fixed and wireless networks evolved in the past 15 years from
circuit-switched voice-centric systems to packet-switched Internet access systems. Due to
the additional complexity of wireless systems, enhancements are usuall y introduced in
fixed-line systems first and only some years later in wireless systems as well. To date,
fixed-line networks offer data rates to the customer premises of several megabits per
second, in some cases already going beyond this. Wireless 3.5G networks are capable of
data rates in the order of several megabits per second. In the future, more bandwidth and
capacity will be achieved by evolving current wireless network technologies (evolved
IMT-2000) and by designing new access networks (IMT-Advanced). This book therefore
not only c oncentrates on 4G systems, but also discusses the evolution of 3G systems.
Another important development is the use of packet-switched networks for transporting
telephone calls, which is referred to as VoIP. This trend is already fully underway in fixedline networks and will inevitably also happen in B3G networks, as systems such as
WiMAX and LTE have been designed without a circuit-switched core network dedicated
to voice calls.
References
1. Background on Fidonet (2008) http://www.fidonet.org.
2. Neuhetzki, T. (December 2005) German long distance tariffs in the 1990s, http://www.teltarif.de/arch/
2005/kw52/s19950.html.
3. Sauter, M. (August 2006) 1000 new mobile phone users a minute, http://mobilesociety.typepad.com/
mobile_life/2006/08/1000_new_mobile.html.
4. Andersen, T. (19 February 2007) Mobile phone lifeline for world’s poor, http://news.bbc.co.uk/1/hi/
business/6339671.stm.
5. 2G and 3G coverage maps (2008) http://www.coveragemaps.com.
6. Sharma, C. (September 2007) Global wireless data market, http://www.chetansharma.com/
globalmarketupdate1H07.htm.
7. The prepaid wireless Internet access Wiki (2008) http://prepaid-wireless-internet-access.wetpaint.com.
8. Shozu (2008) http://www.shozu.com.
9. Lifeblog (2008) http://r2. nokia.com/nokia/0,71739,00.html.
10. Biography of Anssi Vanjoki Executive VP of Nokia Multimedia (2008) http://www.nokia.com/A4126347.
11. The International Telecommunication Union (2006) Detailed specifications of the radio interfaces of
International Mobile Telecommunications-2000 (IMT-2000), ITU-R M.1457-6.
12. The International Telecommunication Union (2003) Framework and overall objectives of the future
development of IMT-2000 and systems beyond IMT-2000, ITU-R M.1645.
2
Beyond 3G Network
Architectures
2.1 Overview
As discussed in Chapter 1, the general trend in telecommunications is to move all
applications to a common transmission protocol, the Internet Protocol. The tremendous
advantage of this approach is that applications no longer require a specific network
technology but can be used over different kinds of networks. This is important since,
depending on the situation, an application might be used best over a cellular network
while at other times it is more convenient and cheaper to use a wireless home or office
networking technology such as Wi-Fi. The increasing number of multiradio devices
supports this trend. Today and even more so in the future, a number of wireless
technologies are deployed in parallel. This is necessary as the deployment of a new
network requires a considerable amount of time and there are usually only a small
number of devices supporting a new network technology at first. It is therefore important
that different network technologies are deployed not only in parallel but also at the same
location. As well as the introduction of new technologies, existing network technologies
continue to evolve to offer improved performance while the new technology is not yet
deployed or is just in the process of being rolled out. For these reasons, this chapter looks
at a number of different Beyond 3G network technologies with an emphasis on those
with the highest market share. In this context, the term ‘Beyond 3G networks’ is used for
cellular networks that offer higher speeds than the original UMTS networks with their
maximum data rate of 384 kbit/s per user.
In the cellular world, the Universal Mobile Telecommunication System (UMTS) with
its High-speed Packet Access (HSPA) evolution is currently the Beyond 3G system with
the broadest deployment. This system, together with its future evolution, HSPAþ,is
therefore discussed first.
Next, the chapter focuses on the successor technology of HSPA and HSPAþ, which is
commonly known as Long Term Evolution (LTE). In the standa rds, LTE is referred to as
Beyond3G–BringingNetworks,TerminalsandtheWebTogether:LTE, WiMAX, IMS, 4G Devices and the Mobile Web 2.0
MartinSauter © 2009JohnWiley&Sons,Ltd. ISBN: 978-0-470-75188-6
14 Beyond 3G – Bringing Networks, Terminals and the Web Together
the Evolved Packet System (EPS), which is divided into the Evolved Packet Core (EPC)
and the Enhanced-UMTS Terrestrial Radio Access Network (E-UTRAN).
While LTE mainly addresses incumbent wireless operators, there is also great interest
from new companies in building wireless networks for Internet access. Many of these
companies are attracted by the Worldwide Interoperability for Microwave Access
(WiMAX) standard, in particular with the 802.16e air interface. WiMAX is very similar
to LTE, but designed from the ground up without the need for backwards-compatibili ty.
Therefore, it is much more suitable for these companies’ needs. Since it is expected that
both LTE and WiMAX will gain considerable market share, both technologies are
discussed to show the similarities and also the differences between the two.
As will be shown throughout this book, 802.11 Wi-Fi networks will play an important
role in overall wireless network architectures of the future. Consequently, this chapter
also introduces Wi-Fi and the latest enhancements built around the original standard,
such as an evolved air interface with speeds of up to 600 Mbit/s, security enhancements
for home and enterprise use and quality of service extensions.
To give an initial idea about the performance of each system, some general observations for each system in terms of bandwidth, speed and latency are discussed. Since these
parameters are of great importance, and often grossly exaggerated by marketing departments, Chapter 3 will then look at this topic in much more detail.
2.2 UMTS, HSPA and HSPAþ
2.2.1 Introduction
Initial drafts of UMTS standards documents appeared in working groups of the Third
Generation Partnership Project (3GPP) at the end of 1999, but work on feasibility studies
for the system began much earlier. A few UMTS networks were opened to the public in
2003, but it was not until the end of 2004, when adequate UMTS mobile phones became
available and networks were rolled out to more than just a few cities, that even early
adopters could afford and actually use UMTS. A time frame of five years from a first set
of specifications to first deployments is not uncommon due to the complexity involved.
This should also be considered when looking at emerging network technologies such as
LTE and WiMAX, which are currently in this window between standardization and
deployment.
2.2.2 Network Architecture
Figure 2.1 shows an overview of the network architecture of a UMTS network. The
upper-left side of the figure shows the radio access part of the network, referred to in the
3GPP standards as the UMTS Terrestrial Radio Access Network (UTRAN).
2.2.2.1 The Base Stations
The UTRAN consists of two components. At the edge of the network, base stations,
referred to in the standards as the NodeB, communicate with mobile devices over the air.
In cities, a base station usually covers an area with a radius of about 1 km, sometimes
g
g
Beyond 3G Network Architectures 15
UE
UTRAN
RNC
NodeB
RNC
NodeB
Core Network
MSC GMSC
HLR
SCP
PSTN
GSM BSS
TRAUTRAU
BSCBSC
BTS
Figure 2.1 Common GSM/UMTS network. (Reproduced from Communication Systems for the
Mobile Information Society, Martin Sauter, 2006, John Wiley and Sons.)
PCUPCU
Data and signalin
SGSN
GGSN
Internet
Server
Signalin
less, depending on the population density and bandwidth requirements. To increase the
amount of data and the number of simultaneous voice calls per base station, the coverage
area is usually split into two or three sectors. Each sector has its own directional antenna
and transceiver equipment. In the standards, a sector is sometimes also referred to as a
cell. A NodeB with three sectors therefore consists of three individual cells. If a user
walked around such a base station during an ongoing voice call or while data was
exchanged, he would be consecutively served by each of the cells. During that time, the
radio network would hand the connection over from one cell to the next once radio
conditions deteriorated. From a technical point of view, there is thus little difference
between a handover between cells of the same base station and between cells of different
base stations. These and other mobility management scenarios will be discussed in more
detail in Section 2.2.3. The radio link between mobile devices and the base station is also
referred to as the ‘air interface’ and this term will also be used throughout this book.
A device using a UMTS network is referred to in the standard as User Equipment (UE).
In this book, however, the somewhat less technical terms ‘mobile’, ‘mobile device’ and
‘connected mobile device’ are used instead.
Today, base stations are connected to the network via one or more 2 Mbit/s links,
referred to as E-1 connections in Europe and T-1 connections in the USA (with a slightly
lower transmission speed). Each E-1 or T-1 link is carried over a pair of copper cables.
An alternative to copper cables is a microwave connection, which can carry several
16 Beyond 3G – Bringing Networks, Terminals and the Web Together
logical E-1 links over a single microwave connection. This is preferred by many operators
as they do not have to pay monthly line rental fees to the owner of the copper cable
infrastructure. To make full use of the air interface capacity of a multisector base station,
several E-1 links are required. The protocol used over these links is ATM (Asynchronous
Transfer Mode), a robust transmission technology widely used in many fixed and
wireless telecommunication networks around the world today. Figure 2.2 shows a typical
base station cabinet located at street level. In practice, base stations are also frequently
installed on flat rooftops close to the antennas, as there is often no space at ground level
and as this significantly reduces the length and thus the cost for the cabling between the
base station cabinet and the antennas.
As technology evolves, using E-1 links over copper cables becomes more difficult
since the number of copper cables leading to a base station is limited and, more
significantly, the line rental costs per month are high. Network operators have therefore
begun using a number of alternative transmission technologies to connect base stations
to the network:
High bandwidth microwave links – a single microwave link can be used to carry
several logical E-1 connections. The latest equipment is capable of speeds exceeding
50 Mbit/s [1].
Fiber links – especially in dense urban areas, many fixed line carriers are currently
deploying additional fiber cables for providing very high data rate Internet access to
businesses and homes. This infrastructure is also ideal for connecting base stations to
the rest of the infrastructure of a wireless network. In practice, however, only a fraction
of deployed base stations already have a fiber laid up to the cabinet.
ADSL/VDSL – a viable alternative to directly using fiber is to connect base stations via
a high-speed VDSL link to an optical transmission network. T-Mobile in Germany is
one operator that has chosen this solution [2]. In some cases, base stations still require
at least one E-1 link for synchronizing the base station with the rest of the network and
for carrying voice calls.
Ethernet – a transmission protocol becoming very popular today in radio access
networks is IP over Ethernet. This is reflected in new designs for UMTS/HSPA base
stations, which can be equipped with E-1 ATM-based interfaces or alternatively via IP
over Ethernet. The Ethernet interface is either based on the standard 100 Mbit/s
100Base-TX twisted pair copper cable interface commonly used with other IT equip-
ment such as PCs and notebooks or via an optical port. In the case of copper cabling,
additional equipment is usually required to transport the Ethernet frames over longer
distances, as 100Base-TX limits cable length to 100 m.
As the technology used for backhauling data from base stations has a significant impact
on the bandwidth and cost of a network, this topic will be discussed in more detail in
Section 3.17.
2.2.2.2 The Radio Network Controllers
The second component of the radio access network is the Radio Network Controller
(RNC). It is responsible for the following management and control tasks:
Beyond 3G Network Architectures 17
The establishment of a radio connection, also referred to as bearer establishment.
The selection of bearer properties such as the maximum bandwidth, based on current
available radio capacity, type of required bearer (voice or data), quality of service
requirements and subscription options of the user.
Mobility management while a radio bearer is established, that is, handover control
between different cells and different base stations of a network.
Overload control in the network and on the radio interface. In situations when more
users want to communicate than there are resources available, the RNC can block new
connection establishment requests to prevent other connections from breaking up.
Another option is to reduce the bandwidth of established bearers. A new data connection might, for example, be blocked by the network if the load in a cell is already at
the limit, while for a new voice call, the bandwidth of an ongoing data connection
might be reduced to allow the voice call to be established. In practice, blocking the
establishment of a radio bearer for data transmission is very rare, as most network
operators monitor the use of their networks and remove bottlenecks, for example by
installing additional transceivers in a base station, by increasing backhaul capacity
between the base station and the RNC or by installing additional base stations to
reduce the coverage area and thus the number of users per base station. Capacity
management will be discussed in more detail in Chapter 3.
2.2.2.3 The Mobile Switching Center
Moving further to the right in Figure 2.1, it can be seen that the RNCs of the network are
connected to gateway nodes between the radio access network and the core network.
In UMTS, there are two independent core network entities. The upper right of the figure
shows the MSC, which is the central unit of the circuit-switched core network. It handles
voice and video calls and forwards SMS messages via the radio network to subscribers.
As discussed in Chapter 1, circuit switching means that a dedicated connection is
established for a call between two parties via the MSC that remains in place while the
call is ongoing. Large mobile networks usually have several MSCs, each responsible for a
different geographical area. All RNCs located in this area are then connected to the
MSC. Each MSC in the network is responsible for the management of all users of the
network in its region and for the establishment of circuit-switched channels for incoming
and outgoing calls. When a mobile device requests the establishment of a voice call, the
RNC forwards the request to the MSC. The MSC then checks if the user is allowed to
make an outgoing call and instructs the RNC to establish a suitable radio bearer. At the
same time, it informs the called party of the call establishm ent request or, if the called
party is located in a different area or different network, establishes a circuit-switched
connection to another MSC. If the subscriber is in the same network it might be possible
to contact the MSC responsible for the called party directly. In many cases, however, the
called party is not in the same network or not a mobile subscriber at all. In this case, a
circuit-switched connection is established to a Gateway MSC (GMSC), shown in
Figure 2.1 on the top right. Based on the telephone number of the called party, the
GMSC then forwards the call to an external fixed or mobile telephone network.
In practice, a MSC usually serves mobile subscribers and also acts as a GMSC.
18 Beyond 3G – Bringing Networks, Terminals and the Web Together
To allow the MSC to manage subscribers and to alert them about incoming calls,
mobile devices need to register with the MSC when they are switched on. At the beginning of the registration process, the mobile device sends its International Mobile
Subscriber Identity (IMSI), which is stored on a SIM card, to the MSC. If the IMSI is
not known to the MSC’s Visitor Location Register (VLR) database from a previous
registration request, the network’s main user database, the Home Location Register, is
queried for the user’s subscription record and authentication information. The authentication information is used to verify the validity of the request and to establish an
encrypted connection for the exchange of signaling messages. The authentication information is also used later on during the establishment of a voice or video call to encrypt the
speech path of the connection. Note that the exchange of these messages is not based on
the IP protocol but on an out-of-band signaling protocol stack called Signaling System
Number 7 (SS7). Out-of-band means that messages are exchanged in de dicated signaling
connections, which are not used for transporting circuit-switched voice and video.
2.2.2.4 The SIM card
An important component of UMTS networks, even though it is very small, is the
Subscriber Identity Module, the SIM card. It allows the network subscription to be
separate from the mobile device. A user can thus buy the SIM card and the mobile device
separately. It is therefore possible to use the SIM card with several devices or to use several
SIM cards with a single device. This encourages competition between network operators,
as users can change from one network to another quickly if prices are no longer competitive. When traveling abroad, it is also possible to buy and use a local prepaid SIM card to
avoid prohibitive roaming charges. Separating network subscriptions from mobile devices
has the additional benefit that mobile devices can not only be bought from a network
operator but also from independent shops, for example electronic stores and mobile phone
shops that sell subscriptions for several network operators. This stimulates competitive
pricing for mobile devices, which would not happen if a device could only be bought from a
single source. A further discussion of this topic can be found in [3].
2.2.2.5 The SMSC
A data service that became very popular long before the rise of current high-speed
wireless Internet access technologies is the short message service, used to send text
messages between users. As the service dates back to the mid 1990s, it is part of the
circuit-switched core network. SMS messages are transported in a store and forward
fashion. When a subscriber sends a message, it is sent via the signaling channel, the main
purpose of which is to transport messages for call establishment and mobility management purposes, to the Short Message Service Center (SMSC). The SMSC stores the
message and queries the Home Location Register database to find the MSC which is
currently responsible for the destination subscriber. Afterwards, it forwards the message,
again in an SS-7 signaling link, to the mobile switching center. When receiving the text
message, the MSC locates the subscriber by sending a paging message. This is necessary,
as in most cases the subscriber is not active when a text message arrives and therefore the
Beyond 3G Network Architectures 19
user’s current serving cell is not known to the MSC. On the air interface, the paging
message is sent on a broadcast channel that is observed by all devices attached to the
network. The mobile device can thus receive the paging message and send an answer to
the network despite not having being in active communication with the network. The
network then authenticates the subscriber, activates encryption and delivers the text
message. In case the subscriber is not reachable, the delivery attempt fails and the
SMSC stores the message until the subscriber is reachable again.
2.2.2.6 Service Control Points
Optional, but very important, components in circuit-switched core networks are integrated databases and control logic on Service Control Points (SCPs). An SCP is required,
for example, to offer prepaid voice services that allow users to top-up an account with a
voucher and then use the credit to make phone calls and send SMS messages. For each
call or SMS, the MSC requests permission from the prepaid service logic on an SCP. The
SCP then checks and modifies the balance on the user’s account and allows or denies the
request. Mobile switching centers communi cate with SCPs via SS-7 connections. When a
prepaid user roams to another country, foreign MSCs also need to communicate with the
SCP in the home network of the user. As there are many MSC vendors, the interacti on
model and protocol between MSCs and SCPs have been specified in the CAMEL
(Customized Applications for Mobile Enhanced Logic) standard [4].
For providing the actual service (e.g. prepaid), only signaling connections between
SCPs and MSCs are required. Some services, such as prepaid, however, also require an
interface to allow a user to check his balance and to top up their account. In practice there
are several possibilities. Most operators use some form of scratch card and an automated
voice system for this purpose. Therefore, there are usually also voice circuits required
between SCP-controlled interactive voice gateways and the MSCs. In addition, most
prepaid services also let users top up or check their current balance via short codes
(e.g. *100#), which do not require the establishment of a voice call. Instead, such short
codes are sent to the SCP via an SS-7 signaling link.
2.2.2.7 Billing
In addition to the billing of prepaid users, which is performed in real time on SCPs,
further equipment is required in the core network to collect billing information from the
MSCs for subscribers who receive a monthly invoice. This is the task of billing servers,
which are not shown in Figure 2.2. In essence, the billing server collects Call Detail
Records (CDRs) from the MSCs and SMSCs in the network and assembles a monthly
invoice for each user based on the selected tariff. Call detail records contain information
such as the identity of the calling party, the identity of the called party, date and duration
of the call and the identity of the cell from which the call was originated. Location
information is required as calls placed from foreign networks while the user is roaming
are charged differently from calls originated in the home network. Some network
operators also use location information for zone-based billing, that is, they offer cheaper
calls to users while they are at home or in the office. Another popular billing approach is
20 Beyond 3G – Bringing Networks, Terminals and the Web Together
Figure 2.2 A typical GSM or UMTS base station cabinet.
to offer cheaper rates at certain times. Most operators combine many different options
into a single tariff and continuously change their billing options. This requires a flexible
rule-based billing service.
2.2.2.8 The Packet-switched Core Network
The core network components discussed so far have been designed for circuit-switched
communication. For communicating with services on the Internet, which is based on
packet switching, a different approach is required. This is why a packet-switched core
network was added to the circuit-switched core network infrastructure. As can be seen in
Figure 2.2, the Radio Network Controller connects to both the circuit-switched core
network and the packet-switched core network. UMTS devices are even capable of having
circuit-switched and packet-switched connections established at the same time. A user can
therefore establish a voice call while at the same time using his device as a modem for a PC,
or for downloading content such as a podcast to the mobile device without interrupting the
connection to the Internet while the voice call is ongoing. Another example of the benefits
of being connected to both the packet-switched and circuit-switched networks is that an
ongoing instant messaging session is not interrupted during a voice call.
Before a mobile device can exchange data with an external packet-switched network
such as the Internet, it has to perform two tasks. First, the mobile device needs to attach
to the packet-switched core network and perform an authentication procedure. This is
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