Brush up on 802.11

Farpoint Group –

The Institute of Electrical and Electronics Engineers (IEEE) is perhaps the most important IT-related standards body, and 802.11 is arguably the most successful IEEE standard after 802.3, which is usually referred to as Ethernet. And, like 802.3, 802.11 is in fact a family of standards. We need to begin with this point because it's a source of significant confusion.

802.11 uses suffix letters to name each working group (WG), the subcommittees that develop specific extensions to the standard. These letters are assigned sequentially over time and no ranking or hierarchy is implied - an important point to remember as we look at each WG below. Also, some WGs are developing extensions to the physical (PHY) layer of the standard, and some are enhancing the medium-access control (MAC) layer.

PHYs are specific definitions of radios (the vehicles that put information on and take it off the air); the MAC is common to all PHYs and contains such functionality as the definition of how individual stations access the airwaves in an orderly fashion, power management, security, and many other functions. Some additional functionality, common to all IEEE 802 networking standards, is defined in IEEE 802.1. This "above the MAC" repository defines such capabilities as the highly-visible 802.1x authentication standard. But the choice of whether to use 802.1 or any other networking strategy or features is usually up to the enterprise or the specific user - it's not part of 802.11.

The original 802.11 standard was approved in June of 1997, after more than seven years of work - a long time by IEEE standards (so to speak). This first standard specified several (incompatible) flavors of one- and two-Mbps PHYs, and a broad range of MAC features - many of which, as it turned out, needed significant additional work. Couple this with the fact that 1 and 2 Mbps just weren't fast enough, and the suffixes began to appear.

The most important of these were 802.11a and 802.11b, both completed in September of 1999. 802.11b defines up to 11 Mbps in the 2.4 GHz. unlicensed band, and 802.11a specifies up to 55 Mbps in the 5+ GHz. bands. Both of these chunks of spectrum are available in various parts of the world, subject, of course, to local regulations. .11b was first to market since it was easier to engineer products based on it. But .11a products are today plentiful and much less expensive than they used to be, and .11a's higher throughput and more available radio channels (12 vs. the three non-overlapping channels in .11b and g) make it attractive in enterprise and consumer-electronics applications. .11b was recently augmented by 802.11g, which essentially takes the higher-performance technology of .11a and applies it to the 2.4 GHz. band, while maintaining backwards compatibility with 802.11b - well, sort of. One can't operate 802.11b and 802.11g simultaneously in a single channel because they're incompatible. A "protection" mechanism makes its possible, however, for the two to coexist in an orderly manner. Regardless, the future belongs to multi-mode client devices that will eliminate the need for the user to worry about any of this - the infrastructure will automatically determine which PHY to use at any given moment in time, with features in the MAC and above allowing connections to be handed off dynamically between a, b, and g.

A number of other extensions have also been approved in the past few years. These include .11c, which specifies WLAN bridging, .11d, which extends .11b to work in more countries, .11f, which specifies interoperability between access points of different manufactures, and .11h, which provides the dynamic frequency selection and transmit power control required for .11a operation in Europe (but is a good idea everywhere regardless). Still in process are .11j, which will quantify the requirements for operation in Japan, and .11k, which will provide a standard mechanism for access to specific radio resource parameters in the interest of optimizing the radio link.

A few other major (and very visible) efforts are also still underway. These include:

** 802.11e: This WG is defining techniques for better time-bounded performance, also called QoS (quality of service). Such extensions are a little problematic, given the nature of the unlicensed radio bands (lots of potential for interference, limited power and range, and so on). But this standard is essential if we're going to make progress in the transmission of voice over IP and digital video, both of which clearly have a bright future on WLANs.

** 802.11i: This group is fixing the very visible security problems with the original standard, which is (in)famously susceptible to hacking and cracking. Most of what's likely to be in .11i is already available in the Wi-Fi Alliance's Wireless Protected Access (WPA) specification, which is now embodied in products from a number of WLAN vendors. Note that WPA isn't a de jure standard since it was not produced by a recognized standards body - but it's a good example of a de facto standard, a common technique for providing at least interim functionality in advance of (and sometimes as an alternative to) a "real" standard. .11i importantly adds to WPA the use of the Advanced Encryption Standard (AES), a very secure encryption technology already in use in many mission-critical applications.

** 802.11n: This recently-established effort is developing a PHY that will provide at least 108 Mbps in a single radio channel. Some vendors have provided non-standard (but still effective) extensions to allow two .11a channels to be ganged together, thereby nominally providing 108 Mbps. .11n will do this in one channel by defining a new PHY - one likely based on a previously-exotic radio technique called MIMO - multiple input, multiple output. Don't worry too much about exactly what that means for now - it requires a bit of explanation. But look for a Farpoint Group White Paper on this topic posted here in November - it's that important. In the meantime, check out Airgo Networks for more information. It is the first company to introduce a WLAN product based on MIMO.

.11e and .11i should be finished by mid-2004, and .11n sometime in 2005. But we just can't rush standards - good standards take a long time because of all of the alternatives that need to be considered, and a process that ensures broad support. Given the tendency of good standards to catalyze the creation of markets and even entire industries, it's in everyone's interest to be thorough. That's 802.11 - and they're not done yet.

Visit the official 802.11 site.

Copyright 2003 by Farpoint Group - All rights reserved.

What’s wrong? The new clean desk test
Join the discussion
Be the first to comment on this article. Our Commenting Policies