What do you want to accomplish? As a sysadmin, this is a question I ask whenever a user comes to me with a new request. It's easy to get wrapped up in implementation details while forgetting exactly what it is you set out to do in the first place. As projects get more complex, it's easy to find yourself "spinning your wheels" without actually getting anywhere.
The most common questions I've encountered about 802.11b networking seem to be the simplest:• How much does it cost?
• How far will it go?
• Can I use it to [ fill in the blank ] ?
Of course, these questions have pat theoretical answers, but they all have the same practical answer: "It depends!" It is easiest to explain how people have applied wireless to fit their needs and answer these questions by way of example.
People are using 802.11b networking in three general applications: point-to-point links, pointto-multipoint links, and ad-hoc (or peer-to-peer) workgroups. A typical point-to-point application would be to provide network bandwidth where there isn't any otherwise available. For example, suppose you have a DSL line at your office but can't get one installed at your house (due to central office distance limits). If you have an unobstructed view of your home from your office, you can probably set up a point-to-point connection to connect the two together. With proper antennas and clear line of sight, reliable point-to-point links in excess of 20 miles are possible (at up to 11Mbps!).
One common way of using wireless in a point-to-multipointapplication is to set up an access point at home to let several laptop users simultaneously browse the Internet from wherever they happen to be (the living room couch is a typical example). Whenever several nodes are talking to a single central point of access, this is a point-to-multipoint application. But pointto-multipoint doesn't have to end at home. Suppose you work for a school that has a fast Internet connection run to one building, but other buildings on your campus aren't wired together. Rather than spend thousands getting CAT5 or fiber run between the buildings, you could use an access point in the wired building with a single antenna that all of the other buildings can see. This would allow the entire campus to share the Internet bandwidth for a fraction of the cost of wiring, in a matter of days rather than months.
The last class of networking, ad-hoc (or peer-to-peer), applies whenever an access point isn't available. In peer-to-peer mode, nodes with the same network settings can talk to each other, as long as they are within range. The big benefit of this mode of operations is that even if none of the nodes are in range of a central access point, they can still talk to each other. This is ideal for quickly transferring files between your laptop and a friend's when you are out of range of an access point, for example. In addition, if one of the nodes in range happens to be an Internet gateway, then traffic can be relayed to and from the Internet, just as if it were a conventional access point. In Chapter 5, we'll see a method for using this mode to provide gateway services without the need for expensive access point hardware. In Chapter 7, we'll build on that simple gateway to create a public access wireless gatekeeper, with dynamic firewalling, a captive web portal, user authentication, and real-time traffic shaping. You can use these modes of operation in conjunction with each other (and with other wired networking techniques) to extend your network as you need it. It is very common, for example, to use a long distance wireless link to provide access to a remote location, and then set up an access point at that end to provide local access.