802.11 Wireless LAN Standard Gains Acceptance

In business environments, 802.11 wireless LANs (WLANs) provide a high-speed connection to the company's Ethernet LAN. Users can roam throughout their facilities while maintaining a wireless connection to the organization's network and the Internet. This growing base of business users is further driving the need for WLANs in the home, as workers demand the same unencumbered connectivity away from the office. In the home, 802.11 is used to connect multiple PCs, peripherals such as printers, and other devices such as PDAs through an Access Point (AP). In addition to being convenient, this arrangement can provide seamless access to the same content between the home and office, creating a simple transition between the two.

Public 802.11 "hotspots" are mushrooming in hotels, coffee shops, libraries, and fast food franchises across North America. For example, T-Mobile HotSpot, the wireless ISP (wISP) division at the cellular telco, took over MobileStar's existing 1,200 Starbucks coffee shops and few dozen other locations when it bought MobileStar's assets out of bankruptcy in early 2002. Since then, it's expanded to 2,200 Starbucks in dozens of municipalities, and has signed deals to install hot spots in all 400-plus Borders book stores and 100 airport club lounges run by American, Delta, and United.

According to Gartner Analyst, Andy Rolfe, the needs of mobile users, including mobile PC and PDA users, will continue to drive the growth of wireless LAN equipment. Rolfe estimates that the penetration of WLAN technology into the professional mobile PC space will grow from 20 percent in 2001 to more than 90 percent in 2007. With an increase in performance, improved security, lower costs, and industry standardization, Rolfe expects wireless networking to increase at a compound annual growth rate of 42 percent through 2007. By the end of 2007, the price of wireless NICs will fall below $30 per unit, and more than two-thirds of mobile computers will ship with integrated WLAN adapters.

The Wireless LAN Association (WLANA) also studied the benefits of wireless networking. It surveyed users and IT professionals in 34 organizations from a cross section of industries (education, healthcare, manufacturing, and retail). The association's study's findings are intriguing. WLANA found that WLANs paid for themselves within the first 12 months in all of the industries it studied.

From a technology viewpoint, Centrino really doesn't break any new ground. When Intel first announced that it was working on a WLAN platform (it was called Banias back then) Intel indicated that the solution would include support for both 802.11b and 802.11a, and the company claimed the mobile processor itself would perform a significant portion of the WLAN baseband and MAC processing that had been previously performed in an external wireless LAN chipset. This was significant, because it indicated that a full-function WLAN chipset like those currently produced from Intersil, Agere, TI, Broadcom, or others would no longer be required with Banias. Instead, early visions for Banias would have only required an add-on radio for a complete WLAN solution. Centrino is a much different solution than that first envisioned. While Intel is still preparing to release an 802.11a+b combo Centrino later this year, the initial product will only support 802.11b, a WLAN standard that is already supported in laptops built by Toshiba, HP, IBM, and Apple. Intel said the Centrino laptops are now available from computer makers such as HP, Dell and Gateway. System pricing is in the range of about $1,399 to $2,000 for the Wi-Fi embedded notebook PCs. While the initial Banias was to be closely integrated on a PC's motherboard, the current Centrino is not unlike most current WLAN solutions that typically reside on an added miniPCI card.

What may be the most interesting technical aspect of the Centrino launch is that it doesn't even represent the latest technology for the very products that it has been launched inside of. For example, Dell used Intel's Centrino announcement to launch its new Inspiron 600m notebook computer. Full-page ads in the Wall Street Journal show Dell's new 600m sporting the new Centrino logo. What the ads don't say, and what is only revealed on Dell's web page, is that for $20 extra, you can upgrade an Inspiron 600m to include integrated 802.11g draft standard support in addition to 802.11b. This upgrade switches from Intel's WLAN chip to one from Broadcom. Dell even offers a full 802.11a/b/g upgrade as an option. (These two optional configurations can't be labeled as Centrino under Intel's rules, even though both upgrades also support 802.11b as does Centrino.)

Figure 1:  The new Intel Centrino mobile technology logo. According to Intel, the logo's design "suggests flight, mobility, and forward movement."

Still, while Centrino might not represent the latest in WLAN technology, it does represent perhaps the biggest political WLAN news so far this year. Intel, with Centrino, is backing WLAN integration in laptops in a big way, and this will not only mean more WLAN enabled laptops, but also more WLAN services to support these laptops, and more WLAN enabled devices that also use these new services. The trickle-down effect will be enormous. Even before Centrino products hit the market, companies such as McDonalds, Starbucks, Circle-K, and others have announced their intentions to offer WLAN access to the Internet to their customers, in many cases for free, or with a small purchase. When Centrino becomes standard in all laptops, even more businesses will take the WLAN plunge.

Meanwhile Microsoft has included features for WLANs in its latest operating system Windows XP. XP can handle multiple WLAN accounts and synchronize files.

Any products tested and approved as "Wi-Fi Certified" (a registered trademark) by the Wi-Fi Alliance are certified as interoperable with each other, even if they are from different manufacturers. A user with a "Wi-Fi Certified" product can use any brand of access point with any other brand of client hardware that also is certified. Typically, however, any Wi-Fi product using the same radio frequency (for example, 2.4 GHz for 802.11b or 11g, 5GHz for 802.11a) will work with any other, even if not "Wi-Fi Certified."

"Wi-Fi Certified has become the global symbol for interoperability between wireless LAN products from different vendors. Accomplishing this has required us to overcome several technical challenges," said Sarosh Vesuna, Wi-Fi Alliance Technical Committee Chairman. "Any organization can make multiple products work together if they are based on a single silicon solution and a set of drivers. However, it is much more complex to certify for the interoperability of products based on several independently developed silicon solutions—the way customers in the enterprise and home use Wi-Fi-based wireless LANs in the real world. Achieving interoperability between different vendors' products requires a rigorous testing protocol. Only products that have passed this testing program are allowed to display the Wi-Fi Certified logo. This testing protocol is one of the reasons corporations and individual consumers have come to trust the Wi-Fi Certified seal of interoperability," continued Vesuna.

Formerly, the term "Wi-Fi" was used only in place of the 2.4 GHz 802.11b standard, in the same way that "Ethernet" is used in place of IEEE 802.3. The Alliance expanded the generic use of the term in an attempt to stop confusion about wireless LAN interoperability.

802.11a operates in the less crowded 5-GHz spectrum and transmits data at a 54 Mbps using OFDM (orthogonal frequency division multiplexing). Where the 2.4-GHz band has three channels for traffic the 5-GHz band has as many as 13 channels. OFDM divides the data signal across 48 separate sub-carriers to provide transmissions of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps of which 6, 12, and 24 Mbps are mandatory for all products. There's enough room in the 5-GHz spectrum to support up to 12 access points operating in the same area without causing interference between access points. For each of the sub-carriers, OFDM uses PSK (phase shift keying) or QAM (quadrature amplitude modulation) to modulate the digital signal depending on the selected data rate of transmission. In addition, four pilot sub-carriers provide a reference to minimize frequency and phase shifts of the signal during transmission. This form of transmission enables OFDM to operate extremely efficiently, which leads to the higher data rates, and minimizes the effects of multi-path propagation.

The 802.11g standard for wireless local area networks, which will extend the data rate of the 802.11b-1999 to 54 Mbps from its current level of 11 Mbps, has been approved by the IEEE's 802.11 Working Group. Final approval is expected in mid-June 2003 with publication in late July 2003. 802.11g will boost wireless LAN speed to 54 Mbps by using OFDM like 802.11a. However, 802.11g maintains the spectral mask and carrier frequencies of the 802.11b standard. Thus the 802.11g specification is backward compatible with the widely deployed 802.11b standard.

By using an enhanced protocol, 802.11g enables mixed network operation. This mixed operation allows legacy 802.11b devices to operate at 11 Mbps while new 802.11g devices operate at 54 Mbps on the same network. This simultaneous operation capability will give users a clean path to upgraded performance without having to be tethered to 802.11b performance when in a mixed network. The extension will improve access to fixed-network LANs and internetwork infrastructures and will also create higher-performing ad-hoc networks.

Even though 802.11g has not been officially finalized, some chip vendors have debuted chipsets that hew to the draft standard. For example Texas Instruments' TNETW1130 is a converged, single-chip medium access controller (MAC) and baseband processor (BBP) for IEEE 802.11a/b/g.

Several other 802.11 working groups exist. 802.11e will provide for standardized Quality of Service (QoS) enhancing voice, video, and other time-bounded or prioritized network traffic. 802.11i is developing an enhanced security spec. 802.11j will specify how products must operate to be used in the newly allocated 4.9 and 5 GHz frequency bands in Japan. 802.11m addresses maintenance issues with 802.11.

Whenever a packet is to be transmitted, the transmitting node first sends out a short ready-to-send (RTS) packet containing information on the length of the packet. If the receiving node hears the RTS, it responds with a short clear-to-send (CTS) packet. After this exchange, the transmitting node sends its packet. When the packet is received successfully, as determined by a cyclic redundancy check (CRC), the receiving node transmits an acknowledgment (ACK) packet. This handshake is necessary to avoid the "hidden node" problem. For example, suppose that node A can communicate with node B, and node B can communicate with node C (Figure 2). However, node A cannot communicate with node C. Thus, for instance, although node A may sense the channel to be clear, node C may in fact be transmitting to node B. The protocol described above alerts node A that node B is busy, and hence it must wait before transmitting its packet.

Figure 2:  Illustration of the "hidden node" problem.

Since its inception, 802.11 has provided some basic security mechanisms to make this enhanced freedom less of a potential threat. For example, 802.11 access points (or sets of access points) can be configured with a service set identifier (SSID). This SSID must also be known by the NIC in order to associate with the AP and thus proceed with data transmission and reception on the network.

Additional security is provided through the 802.11 specifications through the Wired Equivalent Privacy (WEP) algorithm. WEP provides 802.11 with authentication and encryption services. The WEP algorithm defines the use of a 40-bit secret key for authentication and encryption and many IEEE 802.11 implementations also allow 104-bit secret keys. This algorithm provides protection against eavesdropping and physical security attributes comparable to a wired network.

About the Author Charles H. Small is a technical editor based in Waltham, MA.