Articles: Networking

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WLAN users have long been looking forward to the release of the new-generation IEEE 802.11n standard. The related workgroup was established over three years ago and the new standard has been discussed from time to time in computer-related press.

The discussion reached a peak in 2006 as the IEEE commission finally ratified a draft version of the standard. Some manufacturers of network equipment and chips rose to the occasion and introduced a number of devices with support for 802.11n draft.

Being highly interested in this WLAN standard ourselves, we want to check out one of such devices in our labs. We have picked up the WRT300N router from Linksys for that purpose.

Introducing 802.11n

Before getting closer to the Linksys router, we’d want to talk about the 802.11n standard in general. This is indeed a very exciting and important topic at the moment.

The story began in September 2003 when the Institute of Electrical and Electronics Engineers (IEEE) established a workgroup with the n index to develop a new wireless communication standard within the 802.11 family of standards. Why? Because the recently ratified (as of June 2003) 802.11g could not fully meet users’ requirements in terms of speed or coverage. The new standard was expected to make wireless networks as fast as wired ones and to ensure transmissions at a distance of 6 times that of the previous standard. Besides that, 802.11n was to provide compatibility with the earlier shorter-distance wireless communication standards (802.11a/b/g). As might have been expected, the budding standard became the subject of a hot argument right after the establishment of its workgroup. The companies that took part in developing the specification couldn’t come to a compromise and split into two conflicting camps, each with its own vision of what 802.11n was to be. One camp was called WWiSE (World-Wide Spectrum Efficiency) and comprised such firms as Broadcom, STMicroelectronics, Texas Instruments, Airgo Networks, France Telecom, Motorola, etc. It was opposed by TGn Sync (Task Group “n” synchronization) that combined such companies as Agere, Atheros, Intel, Qualcomm, Philips, Panasonic, Sony, and others. The project proposed by WWiSE dominated the discussions of the new standard at first, but it could not gather enough votes in the voting held in January 2005 on Hawaii to be accepted as a first official 802.11n draft. The opposing parties had to join forces eventually to create a unified project. However, in October 2005 some companies (Intel, Broadcom, Cisco, and others) made another attempt to split up the workgroup. They established the Enhanced Wireless Consortium with the presumable goal of speeding up the development process, but which was actually busy developing its own version of the project. As a result, Dell, Motorola, Nokia, Samsung and other companies protested against the EWC and the alternative version of the project was brought up for public discussion. After introducing about 50 amendments, the IEEE commission accepted it as an official version 1.0 draft of the 802.11n standard in January 2006. In January 2007 the same commission approved draft version 1.1 after introducing 3000 corrections into version 1.0 (as many as 12,000 corrections had been proposed at first). The new draft version doesn’t yet introduce any fundamental changes into the specification of the standard. If this goes on, it will only take a firmware or driver update for a device which supports the draft version to begin to support a final version of the 802.11n standard. We should just keep an eye on the ratification process. The final version of the standard is expected to appear in the second half of 2008, some sources even specifying the month, November. But the Wi-Fi Alliance which is responsible for the certification of new wireless equipment does not wan to wait for so long and is planning to begin the certification process as soon as the second quarter of this year.

So what is IEEE 802.11n, technically speaking? Its full draft version is not available to the public, but the fundamentals can be found at websites of some of its developers, e.g. Intel. We’ll use the publicly available information to talk about the technicalities of the new standard.

What benefits is 802.11n going to bring us? First of all, the developers put a focus on the effective bandwidth of the communication channel. That is, the nominal bandwidth is now calculated for the MAC level rather than for the physical level as before. For example, the nominal bandwidth of the 802.11g standard is 54Mbps whereas its effective bandwidth is not higher than 20-25Mbps. For the new standard the effective bandwidth must equal the nominal one or be very close to it at least. And second, the coverage area is increased in the new standard. It is all made possible by utilizing the Multiple Input Multiple Output technique (MIMO) which has been around for a while already. As a matter of fact, the developers of 802.11n didn’t try to invent some revolutionary technologies, but picked up the already available ones instead. This is going to reduce the price of finished solutions and solve the problem of compatibility with such standards as 802.11a and 802.11g/b. It is however clear that MIMO alone cannot increase the channel bandwidth to the declared level. The next speed-improving measure is the twofold expansion of the earlier 20MHz communication channel. Draft version 1.1 specifies that a wide 40MHz channel is formed by two adjacent 20MHz channels. This ensures compatibility because there is no need to introduce a 40MHz channel besides the existing 20MHz one. On the other hand, old network devices, e.g. 802.11g-compliant ones, will be able to communicate with 802.11n equipment.

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