Chi-Yu Huang

802.11 Wireless Networks

This book shows how to build and analyse wireless networks, exploring how an enterprise wireless network with the highest levels of security can be built. The book also explains how to configure wireless network equipment in order implement various network architectures and levels of security. The contents describe how to set up every component of the network, from the client supplicant and the access-points, through to the supporting servers (e.g. RADIUS). Much of the infrastructure is based upon Linux and open source software, but the book also addresses configuration of equipment from three of the largest wireless network equipment providers: Cisco, Alacatel-Lucent (Aruba) and Meru. Furthermore, the book contains coverage of more theoretical topics on performance analysis and monitoring wireless LANs, including the new 802.11n standard.

The Filesystem in Detail

Persistent data is stored in files. Files may contain text, database records, source code or executable instructions, but as far as the kernel is concerned, the content of a file is merely an unstructured byte stream. Files are organised in directories.

Building an Embedded System (First Pass)

In this chapter and the next (Chap. 6) we show how to build embedded GNU/Linux systems. This chapter is a first pass. We use various tools to generate the software components so that we can focus on the structure of the system rather than the details. In Chap. 6 (second pass), we cover the topic in greater depth and construct a system from the source code.

Building an Embedded System (Second Pass)

In the previous chapter we showed how to build an embedded system which ran in a virtual machine. We will refer to this system as the “deb” system to distinguish it from the embedded system described in this chapter.

Overview of GNU/Linux

A full GNU/Linux distribution will also include a large collection of application software (email clients, web browsers, database management systems, compilers, for example) but for the purposes of this chapter, we focus on the four components listed above.

Medium Access Control

The MAC layer implements a number of coordination functions, which are responsible for controlling wireless channel access. The distributed coordination function (DCF) and point coordination function (PCF) are covered. The hybrid coordination function (HCF) from the 802.11e is also discussed.

MAC Layer Performance Analysis

Models of the 802.11 MAC sub-layer are developed and analysed. We show the effects of the RTS/CTS mechanism and fragmentation on performance. We use Maple, a commercial computer algebra system, to analyse these models.

Configuring Wireless Networks

In this chapter, we show how to implement a number of wireless network solutions. We show examples using Cisco, Alcatel-Lucent and Meru equipment. We also show how to implement an open source access-point.

Robust Security Network

In this chapter, we give a detailed description of how to implement a wireless network with enterprise security. Enterprise security requires a RADIUS server for authentication. We show how to configure the FreeRadius for an enterprise WLAN.

Link Rate Adaptation

802.11 devices select modulation techniques (and consequently link speeds) according to the RF environment. In this chapter we develop a number of signal loss models and use them to analyse link rate adaptation. Maple is used extensively throughout this chapter.