Wireless Personal and Local Area Networks / Edition 1

by Axel Sikora

Overview

Wireless LANs are the 'silver bullet' for networks of the future, allowing small communities of office workers, industrial workers, hospital employees, technical teams, etc. to communicate via their mobile devices without having to worry about cables. Scenarios include: small buisnesses where everyone's lap tops are connected the minute they walk through the door so they can move around from office to meeting room and stay on the network throughout; hospital nurses carrying out foetal scans without the need for the scanning device to be connected to the screen; construction sites where the technical foreman can log onto the same system as the architect and compare plans on their respective lap tops. At the moment there are various different technologies, all of which suit different scenarios. Many books discuss wLANs in concept, but do not cover the different technologies, or demonstrate how to build a wLAN with only one of the technologies. This book is unique in presenting the broader picture and providing decision makers with the tools they need to make the appropriate investment for their own situation.
* The only book that gives a broad overview of all the different technologies
* Discusses which technologies are best for different situations and requirements along with business trade-offs
* Gives practical hints and advice on how to implement the technologies
* Includes a chapter on the practical details of operating an IEEE802.11b-wLAN together with application examples
* Covers security considerations

Product Details

ISBN-13:	9780470851104
Publisher:	Wiley
Publication date:	04/02/2003
Pages:	216
Product dimensions:	6.80(w) x 9.90(h) x 0.60(d)

About the Author

Axel Sikora is the author of Wireless Personal and Local Area Networks, published by Wiley.

Read an Excerpt

Wireless Personal and Local Area Networks

---

By Axel Sikora

John Wiley & Sons

ISBN: 0-470-85110-4

---

Chapter One

Introduction

1.1 Definition and restriction

Wireless Local Area Networks (WLANs) are standardised network technologies that implement LAN functionality by using wireless data transfer. This primarily includes the broadband connection of microelectronic devices in a range of tens of meters to a hundred metres. (You will find a more detailed definition of local networks in section 3.1.2.)

There are major differences between WLAN technologies and the other technologies called "wireless" technologies. These differences apply even if some of the applications described in section 2.3 can be implemented with those other wireless technologies. Three areas of wireless messaging that differ from WLAN technologies should be mentioned, in particular:

A wide range of different proprietary systems are available for connecting peripheral devices (for examples, see section 3.1.1). This book does not discuss these systems in any more detail because they do not comply with any particular standard and because they cannot usually be used in a network. A number of different radio relay systems are available, that use light waves (laser links) or electro-magnetic waves to link local networks, like in the application described in section 3.1.5. However, these Point-to-Point (P2P) or Point-to-Multipoint systems (PMP) devices cannot usually be used to createlinked networks.

Digital mobile telephone networks can be used to transfer data, and not just voice traffic. This method is often used for creating a wireless connection to field devices. However, this does not create a local network but a global network with full mobile support. In addition, you cannot generally use this kind of network with a broadband connection. Even the bandwidth of UMTS networks, the technology used for the third generation of mobile telephones, is restricted to a maximum of 2Mbps. In many situations, this bandwidth sinks to values of 384 kbps or even a mere 128 kbps [Sietmann 2001].

1.2 Overview of advantages and disadvantages

The wireless transfer of information has potential advantages for all network hierarchy levels. For some time now, personal and local wireless networks have aroused particular interest because the numerous portable and pocketable devices used for voice and data processing or data transfer via wireless transmission media can connect to each other and communicate directly without the need for a cable. This means that Wireless Local Area Networks (WLANs) can replace the corresponding cabled solutions on the same network level, in such situations.

As a result the tangle of cables under your desk can be reduced or done away with completely. The extra bonus is that there are no more problems with defective cables.

Problems with incompatible connectors (plugs) or missing cables can become a thing of the past.

With regard to cable connections in the office, if wireless technology is used to provide data transfer in the office and at home it can replace expensive cable installations, depending on the network hierarchy level involved.

In ad hoc networking: the functionality available for actively searching for potential communications partners, and for automatically negotiating transfer and application protocols, are of special interest (see section 1.3.10). Many of the most attractive features of wireless technologies can be used with Intelligent Networks (INs) and also implemented in wired systems. This is particularly true if these services occur in the upper protocol layers, regardless of the actual physical transfer route. However, as these services are designed and implemented by the manufacturers of wireless communications systems (and, for the first time in computing, maybe therefore be implemented logically and consistently!), these services are identified with those manufacturer-specific systems.

Using the features of wireless transfer, devices can also be used "on the go". In this case the size of the radio cells, and connections to other systems, depend heavily on which system you use. There are also considerable differences in the speed at which the user can change their location (move about). In addition, as a result of the progressive scaling of semiconductor devices, these products have become increasingly affordable. However, these developments require a high take-up rate and therefore even manufacturers are trying to force the pace of market launch to solve the "chicken or the egg" problem of high numbers of units produced versus low unit costs.

Despite this, the implementation of wireless networks is also subject to a number of limitations:

Cost per bandwidth: Although the cost of wireless systems is going down, the bandwidth for wireless systems is still significantly more expensive than for comparable wired systems. In the case of active components you must reckon on them being a degree of magnitude (10 times) more expensive. However, if you include installation costs, the figures are once again clearly in favour of wireless networks.

Availability of bandwidth: In many cases, not only is the bandwidth for wireless systems more expensive than for wired systems, but less bandwidth is available for wireless systems. In the medium term you can also expect to see costs drop to 10% of their current levels here.

Range: The range of wireless systems is quite restricted in many cases so that the functionality expected by users either cannot be achieved, or can only be achieved to a limited extent (see section 2.4).

Electro-magnetic radiation: Even if the field strengths used for wireless local networks are only 5% of the strength of mobile GSM telephones they increase the electro-magnetic burden on the environment (see section 10.4).

Investment security: At present a wide range of solutions are still available in the market. However, only a few of them will enjoy medium-term commercial success. If investment security is a primary concern, this situation can often delay decisions about future investments.

Interference: Wireless LAN systems transfer data via the air. Unlike wired systems, they use a common medium, known as a shared medium, in the sense that not only the stations in one channel, but also different channels and technologies access the same, shared medium. They do not support switching.

Ruling bodies and international aspects: The fact that transfers in wireless systems take place via the airwaves (a public medium) also means there are numerous organisations that set the regulations governing who can use the various frequency ranges. These regulations cover not only the ranges of useable frequencies but also the permitted modulation procedures, maximum transmitter power, compatibility with other systems and many other issues. Even if the average user is not usually interested in the technical details, they must sometimes take into account the fact that they will not be able (or allowed) to use their own system when they travel abroad.

Security: As the range of a radio transmission is not restricted solely to the area in which the potential recipients are located, but is also broadcast to other areas, there is the risk of it being "overheard" by unauthorised recipients. In addition to this, many systems support automated and dynamic logon for the mobile stations. To close these potential gaps in security, existing systems offer a range of different protective measures. However, the actual levels of security these provide can vary considerably.

As always, the fundamental question for a user is how much value they can add to their application by using a wireless transfer technology.

1.3 Applications overview

1.3.1 Adding value by using a WLAN

Below you will find a number of typical examples to show the value that can be added to actual applications by implementing a WLAN. Section 9.6. describes a selection of real-life installations.

1.3.2 Mobile workstations

Providing support for mobile workstations is probably the first use for WLANs that springs to mind. However, this not only applies to the office environment, in which laptop-based applications can easily be supported in the various conference rooms and offices, but also to teleworking (home office) situations in which you could move your workstation to the garden on sunny days.

1.3.3 Reducing the number of network cable connections

In wireless networks you will require very few network cable connections for communications (or perhaps even none at all). As a result you can either cut the costs of network cable installations, or avoid them entirely. Although modern office buildings are fitted with conduits that make network cables easy and cheap to install, there are still many, many situations where this is not yet the case. For instance, installing network cables in historic buildings can often be either very time-consuming and expensive or even impossible (for example, if the buildings have protected status such as the "listed" status used in the UK). When new companies are founded, their structure, and therefore their infrastructure, can sometimes change radically in a short space of time. It therefore makes sense to find a flexible solution that suits their needs. Also, in the home, cable channels and empty pipes are only rarely available so it is only possible to install additional network cables either by spending a lot of money, or by having cables exposed to view.

The great benefit in reducing the number of network cable connections becomes especially apparent when a large number of remote devices are to be fitted with network connections. The use of wireless networks can provide a crucial advantage in the context of improving the Internet capability of what are known as "embedded systems" [Sikora 2000 (4)].

1.3.4 Training centres

Wireless networks can be implemented in training centres in two ways:

Nowadays, an increasing number of secondary and tertiary students have their own laptops. This is leading to the demise of stationary computer rooms in training centres. Computers owned by students can be networked quite easily in any training room that is fitted with an network access point (AP).

The use of wireless networks makes it easier to set up mobile training rooms for special events, seminars or trade fairs.

1.3.5 Mobile data entry systems

In many situations data entry takes place on site. Typical examples of this are:

stock-taking in commercial companies or warehouses

the analysis of technical devices such as cars or aeroplanes or

data entry in hospitals, during the doctors' rounds, or in operating theatres.

A direct connection to the corporate network enables these applications to compare and synchronise their data with the central database.

1.3.6 Hot spots

Increasingly, waiting times at airports or railway stations or stops at public places are being used for communication via e-mail, or for obtaining information via modern online media. In such situations, wireless networks can provide user-friendly and flexible access to the Internet. It is particularly difficult to implement commercially-viable solutions using, for example, third-generation mobile telephone networks, in small areas that experience high volumes of data traffic (see section 2.1). In these situations WLAN systems are an interesting alternative.

1.3.7 External networking

It is extremely difficult to link local networks in two separate buildings in a LANLAN connection if those buildings are not sited right next to each other. In this case wireless bridges provide a simple and cost-effective alternative to using the public telecommunications network.

1.3.8 Wireless Local Loop

In the same way, WLAN technologies can also be used to supply a wireless domestic connection that runs independently of the public telecommunications network. This Wireless Local Loop (WLL), which is used to bridge the "last mile", can be used for both voice telephony and data networks.

1.3.9 Industrial applications

Many industrial applications in the manufacturing sector run in an environment that is not suitable for cabling. Frequently it is not possible to use cables due to the risk of damage from heat, or physical damage. In addition, buildings are often so large, or otherwise unsuitable, that it is impossible to install cables cost-effectively. In such situations wireless networks have significant advantages.

Flexible production lines provide another interesting area of application because the structure and configuration of the products that are being manufactured change so frequently. The actual implementation of network connections is itself often extremely time-consuming.

1.3.10 Ad hoc networking

Wireless networks can offer the facilities of ad hoc networking in two particular ways, which are described below:

The original meaning of "wireless network" is based on the development of the Aloha network in the late 1960s (see section 2.1.4). This states that stations with a physical connection automatically recognise each other and can therefore communicate with each other [Frodigh 2000]. In this case, the prerequisite is that the stations exchange information before a network connection is established. In addition, these stations must also have the appropriate, reliable security measures to prevent access by unauthorised stations.

The concept of ad hoc networking has grown from this initial point. It now extends to cover not only network connections themselves but also applications which can communicate independently with each other. The original meaning was restricted to the lower layers of the network model but the extended meaning now includes all the layers in a network (see section 2.2.1).

(Continues...)

---

Excerpted from Wireless Personal and Local Area Networks by Axel Sikora Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

---

Table of Contents

Preface xi

Structure of the book xii

1 Introduction 1

1.1 Definition and restriction 1

1.2 Overview of advantages and disadvantages 1

1.3 Applications overview 3

1.4 Market events 6

1.5 Organizations and governing bodies 12

2 Basics 17

2.1 History of wireless vs. wired 17

2.2 Technical communication models and classification 20

2.3 Demands on transfer networks 26

2.4 Properties of electromagnetic waves 28

2.5 Digital modulation technology 33

2.6 Channel access 38

2.7 Spread spectrum techniques 39

2.8 Orthogonal frequency division multiplex procedure 43

2.9 Antennae

2.10 Special features of wireless networks 47

2.11 Frequency allocations 48

3 Applications, devices and standards 51

3.1 Application scenarios 51

3.2 Device types 53

3.3 Standards 54

4 IEEE802.11 57

4.1 The standard 57

4.2 Architectures 59

4.3 Channel access 61

4.4 The Physical layer and bit transfer 81

4.5 Other services 86

4.6 Security 86

4.7 Extensions to the standard 88

5 Bluetooth 95

5.1 The standard 95

5.2 Architectures 99

5.3 Channel access 99

5.4 Controlling states 104

5.5 Bit transfer 108

5.6 Security 110

5.7 System implementation 110

6 DECT 113

6.1 The standard 113

6.2 Architectures 113

6.3 Channel access 114

6.4 Bit transfer 115

6.5 Application profiles 115

7 HomeRF 117

7.1 The standard 117

7.2 Architectures 117

7.3 Channel access 119

7.4 Bit transfer 121

8 HiperLAN/2 123

8.1 The standard 123

8.2 Architectures 125

8.3 Channel access 127

8.4 Bit transfer 130

8.5 Other services 132

8.6 The HiperLAN/2 standard versus IEEE802.1 a 132

9 Operating an IEEE802.11b-complaint WLAN 133

9.1 Introduction 133

9.2 Mobile stations 133

9.3 Access points 136

9.4 Extended networks 141

9.5 Network analysis 143

9.6 Examples from real life 148

10 Various aspects of WLAN technology 153

10.1 Security

10.2 Sources of interference 161

10.3 Selecting a spread spectrum technique 163

10.4 Aspects of EMT interference 165

10.5 WLANs and TCP/IP 167

10.6 Deciding factors 167

10.7 Future prospects 169

Appendix 171

A.1 Maxwellian equations 171

A.2 Physical basis of direct sequence spread spectrum process 171

A.3 Directional antennae 174

B Bibliography 179

B.1 English-language publications 179

B.2 German-language publications 182

C Abbreviations 185