本文发表在 rolia.net 枫下论坛Wireless hits notes in 802.11a, b and g

By Ben Charny
Staff Writer
June 24, 2002, 4:00 AM PT

Millions of people and businesses have installed 802.11b networks--also known as Wi-Fi networks--in the past couple of years, making the technology one of the few bright spots in an otherwise bleak market for PC hardware.

For about $200, an 802.11b network allows Net access within a 300-foot radius, with information moving at up to 11 megabits per second. Considering that most home broadband connections download data at up to 7.1mbps, that speed would seem to be plenty.

So why are manufacturers pushing a much faster, and more expensive, version, called 802.11a? The answer is twofold: 802.11a networks should find greater acceptance in business and, secondly, in the digital home of the future, where the PC will be used as a server to beam information to a range of devices such as TVs and stereos.

802.11a has three main advantages. Chiefly, it offers better security features, a top concern among businesses that have passed on 802.11b. In addition, 802.11a can transmit data up to five times faster, and it can handle more users simultaneously. However, 802.11a equipment doesn't work on 802.11b networks. For example, a person with an 802.11a card in his or her laptop cannot access a home network using an 802.11b base station.

As a result, 802.11a "will show up in the offices not concerned with backward compatibility; it'll be a new deployment in a high-density area with lots of file sharing going on," said Dennis Eaton, senior strategic marketing manger at Intersil, whose designs are licensed to most of the world's 802.11 makers.

A third wave of 802.11 technology is already cresting: 802.11g, which boasts the speed of "a" and is more secure than "b," and has the added benefit of being backward compatible to 802.11b--something the much-touted 802.11a networks are not. However, 802.11g only operates on the same three crowded channels as 802.11b, compared with 802.11a, which runs on 12 channels and reduces interference issues.

Wireless networks using 802.11 standards--regardless of which one--will continue to reign as the champion of home networking, most believe.

The biggest challenger has been identified as Bluetooth, a wireless standard used to emit a very powerful signal but over a range far shorter (only 30 feet) than Wi-Fi's. Mike Hogan, general manager of Texas Instruments' wireless networking business, is among those who believe Bluetooth will never pose a serious threat to 802.11 equipment.

The main reason is that 802.11 was originally built to work specifically with broadband transmissions, while Bluetooth was created to wirelessly connect a phone and headset and other short-range devices such as notebooks, handhelds and printers.

"Trying to extend Bluetooth to be a competitor with 802.11 is an unnatural act," Hogan said.

Another distant challenge is posed by ultrawideband (UWB) technology, which can transfer at speeds of between 400mbps and 500mbps over distances of about 15 feet. It uses a different technique for transmitting data, and it sends many short, sharp pulses of data over a wide frequency, allowing the transfer of large amounts of data over short distances using a relatively low amount of power.

But the technology has been held back by regulatory concerns. The Federal Communications Commission has allowed only limited use because UWB works across wide slices of the radio spectrum that are already licensed to hundreds of government and commercial users. Critics say its powerful signal could cause interference with such devices as satellite navigation tools or government airport radars.


-- The tandem strategy
Although the technology industry is infamous for rapidly making older technologies obsolete, it appears that the already widely used 802.11b technology is deeply entrenched and unlikely to be discarded even as 802.11a catches on.

Although it's true that 802.11a equipment doesn't work on 802.11b networks, that may change as a result of some strong-arming on the part of Microsoft. The software giant will give its coveted Window Hardware Quality Labs (WHQL) seal of approval for the next generation of Windows software only to Ethernet cards that support both 802.11a and 802.11b networks, said Warren Barkley, Microsoft's program manager for wireless and mobility.

"We see both .11a and .11b in the future together, and we think of that as a way for seamless roaming," he said.

Microsoft isn't alone in seeing combination cards as the key to 802.11a's future. Equipment based on just 802.11a will be manufactured and sold, likely ending up in the offices of major businesses installing a wireless network for the first time. But most industry insiders see 802.11a networks living in tandem with 802.11b in order to not abandon the 15 million to 30 million 802.11b wireless networks.

"The future for 'a' is in combination," said In Stat/MDR wireless analyst Alan Nogee.

Combination networks are more costly than 802.11b networks, but "anyone who wants to deploy wireless local area networks will be interested," Intersil's Eaton said.

Major wireless equipment makers such Atheros Communications, Intersil, Agere Systems, Broadcom and Texas Instruments have already begun making 802.11 chipsets that support each of the standards and scenarios. And while wireless equipment based on the 802.11g standard is not on the market yet, major chipmakers are producing chips that use the 802.11g standard.

The competing technologies are causing headaches for the growing number of companies trying to piece together a patchwork of wireless LANs (local area networks) in coffee shops, hotels and other public areas to create a nationwide wireless network.

One such company is Boingo Wireless. The company makes deals with other companies that have set up their own 802.11b networks in places like airport lounges and hotel lobbies. Boingo then sells customers access to more than 600 of these Wi-Fi networks and gives the network owners a slice of any revenue from a subscriber.

Boingo Wireless users can already use an 802.11a network if they have the appropriate equipment, said spokesman Christian Gunning. The company is leaving it up to the operators of the smaller networks to make their own decisions on which of the scenarios to go with, Gunning said.更多精彩文章及讨论，请光临枫下论坛 rolia.net