Hardware Reference
In-Depth Information
doesn't normally cause problems, so it is enabled by the default configuration in most
devices.
Combiningtheuseofthreedatastreamsusingstandard20MHzchannelsandthestandard
800ns guard interval, the maximum throughput of a Wireless-N connection would be
195Mbps. Using the shorter 400ns guard interval would increase this to up to 216.7Mbps.
As with other members of the 802.11 family of standards, 802.11n supports fallback rates
when a connection cannot be made at the maximum data rate.
Table 17.3
compares the standard and optional speeds supported by 802.11n to those sup-
ported by 802.11b, 802.11a, and 802.11g.
Table 17.3 Wireless Network Speeds
As you can see from the table, Wireless-N devices supporting four data streams will be
able to support up to 600Mbps throughput, however the reality today is much less than
this. Because there are no devices on the market that support four streams, the maximum
throughputadvertisedbyWireless-Ndevicestodayiseither300Mbps(usingtwostreams)
or 450Mbps (using three streams), and those figures also assume both the use of 40MHz
wide channels (not normally recommended) and a short guard interval.
TheWi-FiAlliancefirstbegancertifyingproductsthatsupport802.11ninitsDraft2form
in June 2007. The 802.11n standard was finally published in October 2009, and 802.11n
Draft2orlaterproductsareconsideredtobecompliantwiththefinal802.11nstandard.In
some cases, driver or firmware updates might be necessary to insure ensure full compli-
ance. As with previous Wi-Fi certifications, the Wi-Fi 802.11n certification requires that
hardware from different makers interoperate properly with each other. 802.11n hardware
uses chips from makers including Atheros, Broadcom, Cisco, Intel, Marvell, and Ralink.
Bluetooth
Bluetooth is a low-speed, low-power standard originally designed to interconnect laptop
computers, PDAs, cell phones, and pagers for data synchronization and user authentic-
