2.1 The Standards
Here's a brief overview of the current (and future) standards that all fall under the 802 family:
The first wireless standard to be defined in the 802 family was 802.11. It was approved by the IEEE in 1997, and defines three possible physical
: FHSS at 2.4GHz, DSSS at 2.4GHz, and Infrared. 802.11 could achieve data rates of 1 or 2Mbps. 802.11 radios that use DSSS are interoperable with 802.11b and 802.11g radios at those speeds, while FHSS radios and Infrared are obviously not.
According to the specifications available from the IEEE (http://standards.ieee.org/getieee802/), both 802.11a and 802.11b were ratified on September 16, 1999. Early on, 802.11a was widely touted as the "802.11b killer," as it not only provides significantly faster data rates (up to 54Mbps), but operates in a completely different spectrum, the 5GHz UNII
. It uses an encoding technique called Orthogonal Frequency Division Multiplexing (OFDM). While the promise of higher speeds and freedom from interference with 2.4GHz devices made 802.11a sound
, it came to market much later than 802.11b. 802.11a also suffers from range problems: at the same power and gain, signals at 5GHz appear to travel only half as far as signals at 2.4GHz, presenting a real technical
for designers and implementers. The rapid adoption of 802.11b only made matters
, since users of 802.11b gear didn't have a clear upgrade
to 802.11a (the two are incompatible). As a result, 802.11a isn't nearly as ubiquitous or inexpensive as 802.11b, although client cards and
access points (which
two radios, or a single radio with a dual-band chipset) are coming down in price.
Throughout this book, I
discuss 802.11b. It is the de facto wireless networking standard of the last few
, and for good reason. It offers
range and respectable throughput (while the radio can send
at up to 11Mbps, protocol overhead puts the data rate at 5 to 6Mbps, on par with 10baseT wired Ethernet). It operates using DSSS at 2.4GHz, and will automatically select the best data rate (1, 2, 5.5, or 11Mbps), depending on available signal strength. Its greatest advantage at this point is its ubiquity: millions of 802.11b devices have shipped, and the cost of client and access point gear is not only phenomenally low, but many laptop and handheld devices now ship with 802.11b connectivity. Since it can move data at rates much faster than the average Internet connection, 802.11b is widely regarded as "good enough" for general use.
While the 802.11g specification hasn't yet been ratified by the IEEE, it will likely be passed by the time this book goes to press. 802.11g uses the OFDM encoding of 802.11a in the 2.4GHz band, and will also fall back to DSSS to maintain backward compatibility with 802.11b radios. This means that speeds of 54Mbps are theoretically achievable in the 2.4GHz band, all while keeping
compatibility with existing 802.11b gear. This is a very promising technology (so promising, in fact, that the lack of ratification hasn't
some manufacturers from shipping gear that uses the draft standard). In all
, equipment that ships now will be upgradeable to 802.11g via a firmware update once the actual specification is ratified. 802.11g will likely be a massively popular technology; it promises many of the advantages of 802.11a without significantly greater cost while maintaining backward compatibility. For these reasons, 802.11g is poised to become the
major ubiquitous wireless technology.
Approved on December 6, 2001, 802.16 promises to
all of the shortcomings of long-distance applications
by people using 802.11 protocols. It should be pointed out that the 802.11 family was never intended to provide long-distance, metropolitan-area coverage (although I'll show you some examples of people doing exactly that). The 802.16 specification is
designed for providing wireless infrastructure that will cover entire cities, with typical ranges measured in kilometers. It will use frequencies from 10 to 66GHz to provide commercial-quality services to stationary locations (i.e.,
). As I write this, a new extension that will
in the 2 to 11GHz range (802.16a) has just been ratified. This should help significantly with the line-of-sight problems posed by the extremely short waves of 10 to 66GHz. Equipment that implements 802.16 is just now coming to market, and will likely be priced well above the consumer-grade equipment of the 802.11 family.
The 802.1x protocol is not actually a wireless protocol. It describes a method for port authentication that can be applied to nearly any network connection, wired or wireless. Chapter 3 covers 802.1x in more detail.
At this point, the clear front-runner in wireless technology is 802.11b, so I will focus on it for the remainder of this book. Of course, this state of affairs will change as time goes on and consumer demands bring new products to market. For a good overview of 802.11 technologies (including a bunch that I don't have space to cover here), take a look at http://www.80211-planet.com/tutorials/article.php/1439551. You can also download the specifications from the IEEE for yourself at http://standards.ieee.org/getieee802/.
Our original questions (how much does 802.11b cost, how far it will go, and what it is good for) all have the same practical answer: "It depends!" It is
to explain how people have applied wireless to fit their needs and answer these questions by way of example.
People are using wireless networking in three general applications:
. A typical point-to-point application would be to provide network bandwidth where there isn't any
available. For example, suppose you have a DSL line at your office, but can't get one installed at your house (due to CO 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.
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
browse the Internet from wherever they happen to be (the living room
is a typical example). Whenever several nodes are talking to a single, central point of access, this is a
application. But point-to-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. 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, 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 a hardware access point. In Chapter 7, we'll build on that simple gateway to create a public access wireless gatekeeper, with dynamic firewalling, a captive web portal,
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 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. Multiple point-to-point links can also be linked together to create a large network that extends many miles beyond the area of readily available broadband Internet access.