Start planning the wireless LAN as soon as it is clear that you want one. Wireless LANs are still an evolving technology, and the sooner the networking staff is involved, the better it will be. If the wireless LAN is intended for a new building, it would help to involve the network staff as soon as there is a sketch of the basic architecture of the building, especially if there are significant restrictions on the placement of access points. One institution I worked with had a series of tight aesthetic requirements for APs, which forced them to be next to heavy steel structural components, and kept behind paneling. If the network team had been involved earlier, more suitable provision might have been made for AP placement, with a consequent reduction in the amount of money required for the network.
Planning a wired LAN is relatively straightforward at this point. Depending on the size, it may require a fair degree of skill, but fundamentally, the process is well understood. Cable-based network media behave in predictable ways, and the capacity of fixed networks can be upgraded in a straightforward fashion. Wireless LAN technology lacks this level of maturity, which makes the planning process much more important.
Wireless LAN project plans are often referred to as site surveys. Site visits are only one component of installing a wireless LAN, and successful wireless LAN installations often require several visits, each for different purposes. Wireless LANs being designed into a building from the beginning will probably require several visits throughout the construction project. As always, begin planning before "breaking cable" on the network expansion.
Site survey work is the heart of installing a wireless LAN. To successfully run a site survey, though, preparation is very important. Before "breaking cable" on a network expansion, gather technical requirements and information to find out which expectations are important. Use the following checklist to flesh out the network requirements; each point is detailed further in a subsequent section:
How much throughput is required? This is partly dependent on the type of device that will be used on the wireless LAN, although if it is a PC-like device with the ability to display large and complex graphics, you will want your wireless LAN to be as fast as possible. In most cases, this will lead to choosing 802.11a- or 802.11g-based networks to use the 54-Mbps physical layer.
Where should coverage be provided? Everywhere? Some areas are much harder to cover than others. Elevator shafts are usually part of a central building core, and very difficult to cover. Providing coverage within elevator cars themselves is not out of the question, but probably not feasible for most users.
In addition to where the users are located, you will need to pay attention to the number of them. Users may gather more closely in public spots, such as conference rooms, lobbies, and the cafeteria.
The days in which wireless LANs were a cool new technology populated by power users is long gone. A few years ago, it may have been acceptable during a transition phase to have the network merely facilitate automatic reconfiguration. As wireless LANs become more mature, however, architects must design networks that reflect the ideal of continuous connectivity throughout the coverage area.
How many people will use the wireless network, and what quality of service do they expect? As always, be sure to allow for growth!
Will new network cabling be needed to supply the wireless LAN backbone, or can you make do with existing cabling? How will the new access points be powered? Can the access points and antennas be installed in the open or must they be hidden?
To what extent must the wireless LAN hide from public view? Is it acceptable to see the access points, or do they need to be hidden?
Logical network architecture
In most cases, the logical architecture needs to support an IP address block across the entire area of contiguous coverage. Different users may be presented different IP addresses in some of the logical network architectures from Chapter 21. With the recent development of the technology, it is no longer necessary to tailor mobility areas based on IP addressing architecture.
Are any applications sensitive to high or variable delays? Do any applications provide time-critical data?
Before deployment, you will want to design a network that can address many of the security concerns discussed throughout this book, as well as provide a robust environment that supplies some defense against the possibility of future attacks. Security issues and architecture were discussed in the previous two chapters.
Site environmental considerations
A number of factors can affect radio propagation and signal quality. Building materials, construction, and floor plan all affect how well radio waves can move throughout the building. Interference is a fact of life, but it is more pronounced in some buildings than in others. Temperature and humidity have minor effects. Early site visits can assist in anticipating several factors, and a detailed site survey can spot any real problems before installation begins in earnest.
As with many other projects, drawing up a schedule and budget is a necessary component. This chapter does not provide any guidance on nontechnical factors because they are often organization-specific.
Introduction to Wireless Networking
Overview of 802.11 Networks
11 MAC Fundamentals
11 Framing in Detail
Wired Equivalent Privacy (WEP)
User Authentication with 802.1X
11i: Robust Security Networks, TKIP, and CCMP
Contention-Free Service with the PCF
Physical Layer Overview
The Frequency-Hopping (FH) PHY
The Direct Sequence PHYs: DSSS and HR/DSSS (802.11b)
11a and 802.11j: 5-GHz OFDM PHY
11g: The Extended-Rate PHY (ERP)
A Peek Ahead at 802.11n: MIMO-OFDM
Using 802.11 on Windows
11 on the Macintosh
Using 802.11 on Linux
Using 802.11 Access Points
Logical Wireless Network Architecture
Site Planning and Project Management
11 Network Analysis
11 Performance Tuning
Conclusions and Predictions