The Wlan Family Tree

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Before 802.11, wireless LAN technologies were low-speed proprietary offerings. Many used the unlicensed 902-928 MHz ISM (Industrial, Scientific and Medical) band and utilized a spread spectrum modulation technique (see previous chapter) to minimize interference.

Although slow and proprietary (most operated around 500 kilobits per second), these products offered the freedom and flexibility that only wireless networking can provide. So those early WLAN products found a home in industries where mobile workers could use handheld devices for inventory management, data collection, and to deliver patient information right to the bedside. By 1991, Aironet, Symbol Technologies and others were marketing their proprietary 900 MHz wireless LAN technologies in earnest.

It wasn't long before wireless vendors began developing proprietary 2.4 GHz WLAN products, opening up additional markets, especially in the warehousing and educational sector. Educational institutions were just beginning to embrace the Computer Age by wiring classrooms. However, many institutions quickly learned the difficulty of wiring rooms in older, established universities occupying 18th and 19th century buildings. For those institutions, wireless networking effectively overcame the physical limitations encountered on many campuses.

The IEEE

Next, the reader should be aware of the importance of the Institute of Electrical and Electronic Engineers (IEEE), an international professional organization for electrical and electronics engineers, with formal links with the International Organization for Standardization (more commonly known as the "ISO"). Within the IEEE 802 Committee are a number of Working Groups that strive to define different aspects of LANs and MANs.

IEEE became aware of the first non-standard wireless LAN protocols, which operated in the 900 MHz band, in the late 1980s. Thereafter the IEEE 802 LAN/MAN Standards Committee set on a course toward the development of a set of standards for wireless LANs.

In 1990, the IEEE 802 Executive Committee established the 802.11 Working Group to create a wireless local area network standard. Under the chairmanship of Vic Hayes, an engineer from NCR (one of the leading global technology companies), the 802.11 Working Group began to develop a WLAN specification. During the course of the project, that Working Group found it necessary to form individual Task Groups to work on different aspects of the 802.11 standard. The standards that these Task Groups define are suffixed by the Task Group's letter (e.g. 802.11a Task Group). That is how the story of the now-standard designations of "802.11a," "802.11b," "802.11g," etc., came to exist.

Now let's look back to when the progenitor of today's Wi-Fi technology saw its first breath of life.

The Original 802.11 Specification

On June 26, 1997, seven years after the formation of the 802.11 Working Group, the IEEE Standards Board approved the first 802.11 standard. It was thereafter published on November 18, 1997.

The original 802.11 specification, which provides data transfer rates of 1 and 2 Mbps, specifies an over-the-air interface between a wireless client and a base station (i.e. access point) or between two wireless clients. It specifies an operating frequency in the unlicensed 2.40-2.483 GHz ISM (Industrial, Scientific, and Medical) band. But in 1997, for a wireless networking product to operate in the ISM bands, it must use some form of "spread spectrum" modulation, which, as it name implies, "spreads" a signal's power over a wide band of frequencies. This original 802.11 specification provided one of two incompatible forms of spread spectrum modulation, either frequency hopping or direct sequence. Since both techniques spread the signal over more than one frequency in order to boost signal-to-noise performance (a technique called "process gain"), it wastes bandwidth. Moreover, the specification required WLANs that operate at the 1 Mbps level to employ a binary phase shift keying (BPSK) modulation scheme, while systems that are designed to operate at the 2 Mbps level must operate off a quadrature phase-shift keying (QPSK) modulation scheme.

Figure 6.1: The OSI model in relation to the IEEE's 802.11 specifications.

The initial 802.11 specification also describes the OSI's (Open System Interconnection) Data Link Layer's MAC (Medium Access Control) sublayer, and the PHY (Physical) Layer definitions. To date, all of the ensuing amendments and supplemental 802.11 standards are either enhancements to the original MAC for QoS (Quality of Service) and security, or an extension to the original PHY for high-speed data transmission.

What's most important about 802.11 though, is that this standard laid the groundwork for future technologies. Today's wireless networking boom owes its emergence to the innovative path starting from that original IEEE WLAN specification.

The Ethernet Connection

In the wired world, 802.3 Ethernet is the predominant LAN technology. Its evolution is analogous to Wi-Fi. To fully appreciate Wi-Fi's role in today's networking environments, you must understand the Wi-Fi / Ethernet relationship.

The IEEE's 802 Executive Committee mandate is to design specifications to standardize the physical path over which computers communicate. Toward that end, the Committee formed the 802.3 Working Group to define the physical media and the working characteristics for physical communication in a LAN environment. The result was an Ethernet-like standard published in 1985. This first publication was named "IEEE 802.3 Carrier Sense Multiple Access with Collision Detection Access Method and Physical Layer Specifications." As such, it defines the Physical Layer and the Data Link Layer's MAC sublayer, including specifying cabling options, data transmission method, and means for controlling access to the cable.

Originally providing for ten megabit per second (Mbps) transfer rates, the 802.3 Working Group continues to keep pace with the data rate and throughput requirements of contemporary LANs. That's why the 802.3 standard, albeit with many extensions, still governs how computers communicate today.

This set of specifications is more commonly known as "Ethernet," although the IEEE's document doesn't refer to 802.3 as "Ethernet," per se. "Ethernet" is a specific product trademarked by Xerox, whereas 802.3 is a set of standards that can be used by anyone.

802.3 Ethernet provides an evolving, high-speed, widely available and interoperable networking standard. Furthermore, the IEEE 802.3 standard is open. An open standard is defined as a technical standard that has been accepted by a bona fide standards organization such as the American National Standards Institute (ANSI) or the European Technical Standards Institute (ETSI). The open standard status of 802.3 serves to decrease barriers to market entry, and results in a wide range of suppliers, products, and price points from which end-users can choose to build their LANs. And, most importantly, conformance to the Ethernet standards allows for interoperability, enabling users to select individual products from a multiplicity of vendors, secure in the knowledge that the products will work together.

Where the 802.3 Ethernet standard allows for data transmission over twisted-pair and coaxial cable, the 802.11 WLAN standard allows for transmission over different media, e.g. radio frequency and infrared light. But since 802.11 networks are considered wireless extensions of wired Ethernet, the 802.11 specifications were designed to work within a mixed Ethernet/Wi-Fi environment. Thus, 802.11 networks can handle conventional wired networking protocols such as TCP/IP, AppleTalk, and PC file sharing standards.

Wi-Fi also seems to be heading down the same "generic term" path of Ethernet, i.e. it is being used to describe all 802.11 networks, much the same way that "Ethernet" describes all IEEE 802.3 networks.

The Birth of Wi-Fi

The Wi-Fi story begins at the Institute of Electrical and Electronic Engineers (IEEE). The IEEE's 802 LAN/MAN Standards Committee defines standards for Local Area Networks (LANs) and Metropolitan Area Networks (MANs), including Ethernet, Token Ring and Wi-Fi.

Since the initial IEEE 802.11 standard was adopted officially in 1997, we have seen the data rate rise from 1 or 2 Mbps to 11 Mbps, and then to 54 Mbps.

Even as it ratified the 802.11 standard, the IEEE 802 Executive Committee knew that as the world became more bandwidth-hungry, a more robust and faster wireless networking technology would be needed. Therefore, the Committee continued its work. Within 24 months, the Working Group approved not one, but two, Project Authorization Requests for higher rate PHY Layer extensions to 802.11; both were designed to work with the existing 802.11 MAC Layer. One was IEEE 802.1la operating in the U-NII bands at 5 GHz, and the other was IEEE 802.11b operating in the ISM band at 2.4 GHz. In late 1999, the IEEE published these two supplements.

That's about the time the term "Wi-Fi" entered the picture. Originally, the term "Wi-Fi," as promulgated by WECA (now known as the Wi-Fi Alliance), was to be used only in place of the 2.4 GHz 802.11b standard. However, in October 2002, the Wi-Fi Alliance extended the "Wi-Fi" trademark to include the non-compatible 802.11a standard, which supports bandwidths up to 54 Mbps. Furthermore, the Alliance has indicated that since 802.11g is finalized, it is taking the necessary steps to also extend the "Wi-Fi" trademark to products built upon that standard's specifications.

WHY "b" BEFORE "a"?

There's some confusion about why 802.11b products came before 802.11a. So let's figure out what happened-you will need some history and a scorecard to keep the versions straight.

First, the reader must understand that while there are strong similarities between 802.11a and 802.11b, there are also important differences. Next, you need to appreciate that the IEEE had to find a means (1) for attaining both the high data rates needed to make WLANs a viable option, which in turn requires spectrum (an allocation of frequencies that the specification can use), and (2) for optimizing certain power requirements, which must be low enough to prevent interference with other users of the same frequencies, but at the same time strong enough to allow for consistent data rate speeds. The IEEE succeeded. Both 802.11a and 802.11b products address those needs, and, in some instances, 802.11a does a superior job. But that alone wasn't enough to propel 802.11a into a dominant role.

Hindering 802.11a's acceptance in the marketplace is its overall cost of installation, which is significantly higher than the cost of an 802.11b network. The distance that signals travel is related to their frequency-the lower the frequency, the further they will travel (for a given amount of power). This means that considerably more access points (APs) are needed for wireless LANs that use the higher frequency U-NII band than for those that use the lower frequency ISM band.

Another reason that 802.11b gained dominance in the marketplace was that after the IEEE's approval of 802.11a, its U-NII spectra, which is a huge amount of spectrum (more than many conventional broadcast television channel bandwidths combined), were put under scrutiny, not only by regulatory agencies, but also by the manufacturing sector. This gave 802.11b time to develop a strong installation base.

The 802.11a's OFDM waveform also initially caused some consternation in the manufacturing sector, because it is more difficult to implement than the forms of modulation used by 802.11b. (It's interesting to note that when 802.11a was ratified in 1999, very few designers had been exposed to OFDM.)

Finally, and perhaps the most important reason why 802.11b became a international de facto standard for WLANs and why its gear arrived first, was because there was already near worldwide acceptance of the 802.11b's 2.4 GHz range for low power, and usually license-free, operation. Cordless phones, microwave ovens, and baby monitors already use this spectrum (as do HomeRF networking and Bluetooth devices). Conversely, in many parts of the world, 802.11a's spectra weren't (and in some places still aren't) readily available for the public's use (the U.S. being one of the notable exceptions).

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