Guide to Deploying 802.11n Wireless LANs

By Fluke Networks
Posted July 2009

Abstract:

The Institute of Electrical and Electronics Engineers (IEEE) first defined wireless local area networking technology in 1997 in the original 802.11 standard. Wireless LAN (WLAN) networking products supported data rates of 1 and 2 Mbps using the RF technologies of either Direct Sequencing Spread Spectrum (DSSS) or Frequency Hopping Spread Spectrum (FHSS). Since 1997, WLAN data rates have gradually increased as the 802.11 standard has been amended to support new technologies. Orthogonal Frequency Division Multiplexing (ODFM) technology brought data rates of 6 - 54 Mbps to 5 GHz frequency bands with the ratification of the 802.11a amendment in 1999. In the same year, the 802.11b amendment defined High-Rate Direct Sequencing Spread Spectrum (HR-DSSS) mechanisms that brought higher data rates of 5.5 and 11 Mbps to the more commonly used 2.4 GHz frequency band. The IEEE ratified the 802.11g amendment in 2003 which also brought OFDM technology and the data rates of 6 - 54 Mbps to the 2.4 GHz frequency band. Consumers and businesses have long anticipated the ratification of the 802.11n draft amendment which defines the use of High Throughput (HT) radios which have the potential to support data rates as high as 600 Mbps. 802.11n technology uses both PHY and MAC layer enhancements to achieve these high data rates.

The 802.11n draft amendment is scheduled to be ratified sometime in 2009. Very often, new 802.11 technologies do not find their way into the enterprise until a year or more after ratification of an 802.11 amendment. However, 802.11n technology is already being deployed in the enterprise prior to ratification of the 802.11n amendment. Most of the major Wi-Fi vendors debuted enterprise 802.11n solutions in 2008 and have already begun to direct their customers to High Throughput (HT) technology. The advent of this new technology also brings new challenges when designing and deploying an 802.11n WLAN. In the past, WLANs were designed to compensate for the negative effects of the RF phenomena of multipath. When designing an 802.11n WLAN, multipath now provides an advantageous effect. 802.11n also presents unique challenges when integrating the technology into a pre-existing wired network infrastructure. Using standard Power over Ethernet (PoE) to remotely power access points may no longer be possible. The increased bandwidth from multiple 802.11n access points might also create backhaul “bottlenecks” anywhere from the access layer to the core layer of the wired network infrastructure. Another design and integration challenge is how the 802.11n radios will affect current 802.11a/b/g transmissions and vice versa. New security considerations may also have to be addressed with Wireless Intrusion Detection Systems (WIDS) when monitoring an 802.11n WLAN. This paper will discuss the basics of 802.11n technology as well as all of the unique design and integration challenges. This paper will also outline nine recommendations for deploying and migrating to 802.11n WLANs.