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Chapter 1, Introduction to Wireless Networking, lists ways in which wireless networks are different from traditional wired networks and discusses the challenges faced when adapting to fuzzy boundaries and unreliable media. Wireless LANs are perhaps the most interesting illustration of Christian Huitema's assertion that the Internet has no center, just an ever-expanding edge. With wireless LAN technology becoming commonplace, that edge is now blurring.
Chapter 2, Overview of 802.11 Networks, describes the overall architecture of 802.11 wireless LANs. 802.11 is somewhat like Ethernet but with a number of new network components and a lot of new acronyms. This chapter introduces you to the network components that you'll work with. Broadly speaking, these components are stations (mobile devices with wireless cards), access points (glorified bridges between the stations and the distribution system), and the distribution system itself (the wired backbone network). Stations are grouped logically into Basic Service Sets (BSSs). When no access point is present, the network is a loose, ad-hoc confederation called an independent BSS (IBSS). Access points allow more structure by connecting disparate physical BSSs into a further logical grouping called an Extended Service Set (ESS).
Chapter 3, 802.11 MAC Fundamentals, describes the Media Access Control (MAC) layer of the 802.11 standard in detail. 802.11, like all IEEE 802 networks, splits the MAC-layer functionality from the physical medium access. Several physical layers exist for 802.11, but the MAC is the same across all of them. The main mode for accessing the network medium is a traditional contention-based access method, though it employs collision avoidance (CSMA/CA) rather than collision detection (CSMA/CD). The chapter also discusses data encapsulation in 802.11 frames and helps network administrators understand the frame sequences used to transfer data.
Chapter 4, 802.11 Framing in Detail, builds on the end of Chapter 3 by describing the various frame types and where they are used. This chapter is intended more as a reference than actual reading material. It describes the three major frame classes. Data frames are the workhorse of 802.11. Control frames serve supervisory purposes. Management frames assist in performing the extended operations of the 802.11 MAC. Beacons announce the existence of an 802.11 network, assist in the association process, and are used for authenticating stations.
Chapter 5, Wired Equivalent Privacy (WEP), describes the Wired Equivalent Privacy protocol. In spite of its flaws, WEP is the basis for much of the following work in wireless LAN security. This chapter discusses what WEP is, how it works, and why you can't rely on it for any meaningful privacy or security.
Chapter 6, User Authentication with 802.1X, describes the 802.1X authentication framework. In conjunction with the Extensible Authentication Protocol, 802.1X provides strong authentication solutions and improved encryption on Wireless LANs.
Chapter 7, 802.11i: Robust Security Networks, TKIP, and CCMP, describes the 802.11i standard for wireless LAN security. In recognition of the fundamental flaws of WEP, two new link-layer encryption protocols were designed, complete with new mechanisms to derive and distribute keys.
Chapter 8, Management Operations, describes the management operations on 802.11 networks. To find networks to join, stations scan for active networks announced by access points or the IBSS creator. Before sending data, stations must associate with an access point. This chapter also discusses the power-management features incorporated into the MAC that allow battery-powered stations to sleep and pick up buffered traffic at periodic intervals.
Chapter 9, Contention-Free Service with the PCF, describes the point coordination function. The PCF is not widely implemented, so this chapter can be skipped for most purposes. The PCF is the basis for contention-free access to the wireless medium. Contention-free access is like a centrally controlled, token-based medium, where access points provide the "token" function.
Chapter 10, Physical Layer Overview, describes the general architecture of the physical layer (PHY) in the 802.11 model. The PHY itself is broken down into two "sublayers." The Physical Layer Convergence Procedure (PLCP) adds a preamble to form the complete frame and its own header, while the Physical Medium Dependent (PMD) sublayer includes modulation details. The most common PHYs use radio frequency (RF) as the wireless medium, so the chapter closes with a short discussion on RF systems and technology that can be applied to any PHY discussed in the book.
Chapter 11, The Frequency-Hopping (FH) PHY, describes the oldest physical layer with 802.11. Products based on the FH PHY are no longer widely sold, but a great deal of early 802.11 equipment was based on them. Organizations with a long history of involvement with 802.11 technology may need to be familiar with this PHY.
Chapter 12, The Direct Sequence PHYs: DSSS and HR/DSSS (802.11b), describes two physical layers based on direct sequence spread spectrum technology. The initial 802.11 standard included a layer which offered speeds of 1 Mbps and 2 Mbps. While interesting, it was not until 802.11b added 5.5 Mbps and 11 Mbps data rates that the technology really took off. This chapter describes the two closely-related PHYs as a single package.
Chapter 13, 802.11a and 802.11j: 5-GHz OFDM PHY, describes the 5-GHz PHY standardized with 802.11a, which operates at 54 Mbps. This physical layer uses another modulation technique known as orthogonal frequency division multiplexing (OFDM). Slight modifications were required to use this PHY in Japan, which were made by the 802.11j standard.
Chapter 14, 802.11g: The Extended-Rate PHY (ERP), describes a PHY which uses OFDM technology, but in the 2.4 GHz frequency band shared by 802.11b. It has largely supplanted 802.11b, and is a common option for built-in connectivity with new notebook computers. The PHY itself is almost identical to the 802.11a PHY. The differences are in allowing for backwards compatibility with older equipment sharing the same frequency band.
Chapter 15, A Peek Ahead at 802.11n: MIMO-OFDM, describes the PHY currently in development. 802.11n uses a PHY based on multiple-input/multiple-output (MIMO) technology for much higher speed. At the time this book went to press, two proposed standards were dueling in the committee. This chapter describes both.
Chapter 16, 802.11 Hardware, begins the transition from theoretical matters based on the standards to how the standards are implemented. 802.11 is a relatively loose standard, and allows a large number of implementation choices. Cards may differ in their specified performance, or in the manner in which certain protocols are implemented. Many of these variations are based on how they are built.
Chapter 17, Using 802.11 on Windows, describes the basic driver installation procedure in Windows, and how to configure security settings.
Chapter 18, 802.11 on the Macintosh, describes how to use the AirPort card on MacOS X to connect to 802.11 networks. It focuses on Mac OS X 10.3, which was the first software version to include 802.1X support.
Chapter 19, Using 802.11 on Linux, discusses how to install 802.11 support on a Linux system. After discussing how to add PC Card support to the operating system, it shows how to use the wireless extensions API. It discusses two common drivers, one for the older Orinoco 802.11b card, and the MADwifi driver for newer cards based on chipsets from Atheros Communications. Finally, it shows how to configure 802.1X security using xsupplicant.
Chapter 20, Using 802.11 Access Points, describes the equipment used on the infrastructure end of 802.11 networks. Commercial access point products have varying features. This chapter describes the common features of access points, offers buying advice, and presents two practical configuration examples.
Chapter 21, Logical Wireless Network Architecture, marks the third transition in the book, from the implementation of 802.11 on the scale of an individual device, to how to build 802.11 networks on a larger scale. There are several major styles that can be used to build the network, each with its advantages and disadvantages. This chapter sorts through the common types of network topologies and offers advice on selecting one.
Chapter 22, Security Architecture, should be read in tandem with the previous chapter. Maintaining network security while offering network access on an open medium is a major challenge. Security choices and architecture choices are mutually influential. This chapter addresses the major choices to be made in designing a network: what type of authentication will be used and how it integrates with existing user databases, how to encrypt traffic to keep it safe, and how to deal with unauthorized access point deployment.
Chapter 23, Site Planning and Project Management, is the final component of the book for network administrators. Designing a large-scale wireless network is difficult because there is great user demand for access. Ensuring that the network has sufficient capacity to satisfy user demands in all the locations where it will be used requires some planning. Choosing locations for access points depends a great deal on the radio environment, and has traditionally been one of the most time-consuming tasks in building a network.
Chapter 24, 802.11 Network Analysis, teaches administrators how to recognize what's going on with their wireless LANs. Network analyzers have proven their worth time and time again on wired networks. Wireless network analyzers are just as valuable a tool for 802.11 networks. This chapter discusses how to use wireless network analyzers and what certain symptoms may indicate. It also describes how to build an analyzer using Ethereal, and what to look for to troubleshoot common problems.
Chapter 25, 802.11 Performance Tuning, describes how network administrators can increase throughput. It begins by describing how to calculate overall throughput for payload data, and common ways of increasing performance. In rare cases, it may make sense to change commonly exposed 802.11 parameters.
Chapter 26, Conclusions and Predictions, summarizes current standards work in the 802.11 working group. After summarizing the work in progress, I get to prognosticate and hope that I don't have to revise this too extensively in future editions.
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