The upcoming IEEE 802.11n wireless standard will enable high-bandwidth applications such as streaming video to
coexist with wireless VoIP. But before deploying products based on the new standard, you must understand how 802.11n achieves higher data rates, the risks associated with initial products, the impact on your existing network, and the environments in which the new standard will provide the greatest benefit. This article is the first of two that describe the 802.11n wireless standard and the issues you must consider before deploying the new technology.
The IEEE began work on 802.11n in January 2004. Work proceeded through 2004 and 2005, with Draft 1.0 of the proposed standard released for review in January 2006. The committee received more than 6,000 comments and requests for change and began working to incorporate the requested improvements in May 2006. The committee completed Draft 1.06 in November and expects to finish incorporating additional changes in January 2007. It will then begin work on Draft 2.0. Final completion and acceptance of the standard is not expected until early in 2008.
The current version of the standard promises a data rate as high as 540 Mbits/second. Typical throughput should be in the 100 to 200 Mbits/second range, with potential for higher levels as the technology matures.
The increase is achieved through the use of Multiple Input Multiple Output (MIMO) technology, a wider radio frequency channel, and a method to decrease the time between transmissions.
MIMO uses multiple antennas at the sending and receiving stations to achieve increases in both data rate and range. Data rate increases as the number of antennas on the sending and receiving stations increase. It is not necessary for the number of antennas on the sending station to equal the number on the receiving station.
Signals from the individual antennas take different paths from the sender to the receiver. Signals bounce off obstacles along the way and arrive at slightly different times. With current wireless technology, bounced signals can prevent correct reception, but with MIMO, the receiver uses the multiple signals to reconstruct the original data stream. The fact that obstacles in the path actually contribute to the ability of the receiver to reconstruct the signal means that 802.11n equipment can operate over much larger distances and with fewer dead spots than current technology.
Part of 802.11n's speed increase results from the use of a wider frequency channel. Current wireless technologies use a 20 MHz channel. The 802.11n draft allows use of a 40 MHz channel.
Much time is wasted in a wireless network as stations contend for the authority to send. Many packets are very short, but current technologies require that the sending station contend for the channel, send one packet, release the channel, and then contend again in order to send the next packet. IEEE 802.11n supports frame aggregation. Once a station gains the authority to transmit, it can transmit a series of frames without the requirement to release and regain authority for each frame.
IEEE 802.11n will operate on either the 2.4 GHz band or the 5 GHz band. Operation on the 2.4 GHz band can mean interference with an existing 802.11b or 802.11g network. Only three 20 MHz channels are available on the 2.4 GHz band. If an 802.11n network uses a 40 MHz channel, it will consume two of the three channels. Similarly, when operating on the 5 GHz band, 802.11n can interfere with an existing 802.11a network.
Although IEEE 802.11n will deliver higher performance in all environments, it will have its greatest impact indoors. Since MIMO takes advantage of bouncing off obstacles, it will offer less improvement outdoors, where the path between sender and receiver is more likely to be clear of obstacles. Actual performance will depend on details of the network environment.
The benefits of higher speed and longer range will guarantee that IEEE 802.11n will be widely adopted, but you must understand its impact on your network before rushing to deploy. The next article will explore these issues.
Continue reading part two, IEEE 802.11n: Research carefully before deploying.
About the author:
David B. Jacobs of The Jacobs Group has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies, as well as software startups.