In theory, 802.11n can zip by your 100Mbps Fast Ethernet at a real-world 160Mbps, but the practice it's usually much slower. No, the Wi-FI vendors aren't lying; the problem is that you have to set 802.11n up just right to really get fast performance.
First, you need to make sure that you're using up-to-date 802.11n hardware. Older 802.11n equipment, built before the 802.11n standard was finalized in late 2009, may not work and play well with your newer devices. There were many 802.11n draft access points (APs), network interface cards (NICs) and chipsets and each vendor used its own best guess on what the standard would eventually look like.
Thanks to all this older, not quite standard 802.11n hardware, we have two problems. The first is that some older hardware, unless the firmware can be upgraded, won't work at full 802.11n speeds with your newer standardized equipment. The other is that you can be almost certain that older APs, switches, or routers from one vendor won't work well with another vendor's equipment. Oh, it may look like it's working, but if you check you'll often find that your Wi-Fi's connection is only running at 802.11g's 54Mbps.
Of course, if your office is like most, you almost certainly still have a lot of 802.11g compatible laptops in work. You might think that since 802.11n is backwards compatible with 802.11g that you'll do just fine by replacing your 802.11g APs with 802.11n hardware. You'd be wrong.
802.11n AP will support 802.11g client hardware just fine, but letting 802.11n AP support 802.11g comes with a painful performance hit. While 802.11n devices working in the 2.4GHz band are backwards compatible with 802.11g, or even 802.11b, faster 802.11n equipment will lose about half its potential speed. So, instead of seeing say 100Mbps of throughput from 802.11n AP to the 802.11n laptops, you'll only see 50Mbps.
My fix for this is to keep 802.11g APs running until the last of the 802.11g PCs go to that big junk-pile in the Wi-Fi sky. It's worked well for me.
You also should use 802.11n's channel bonding to increase throughput. On your APs, you'll find this option labeled 'double-wide' channels. This in an ancient technique that's used to increase throughput by using two channels at once to deliver data. Then, as now, it works well.
There' a 'gotcha' though. A Wi-Fi's channel is required to be 20MHz. Thus, just like the name says, a 'double wide' takes up 40MHz of radio room instead of the usual 20MHz. The problem is that there's only room for three 20MHz channels in 802.11b/g/n's 2.4GHz radio spectrum. If you run out of Wi-Fi spectrum room, your overall network throughput will decline. Even if you're doing a good job of managing your network space, your available channels are likely to also be used by your next-door neighbors' Wi-Fi set-up.
The easiest way to dodge this potential problem, for now, is to use the higher 5GHz range. Far fewer people are currently using the 5GHz range. This will change as more people switch over to 802.11n, but for now it's the easiest way to use wide channels to increase your effective bandwidth without running into interference. The one downside is that 5GHz has less range than 2.4GHz.
That's why I prefer to use dual-band APs that support both 2.4GHz and 5GHz. Best of all is equipment that supports using both 2.4GHz and 5GHz at the same time for the maximum in flexibility, such as the Linksys Simultaneous Dual-N Band Wireless Router WRT610N. Older 802.11n hardware, such as the first generation of Apple's AirPort Extreme, as well as some entry-level APs, can only support 2.4GHz or 5GHz
High-performance 802.11n equipment also comes with a larger number of multiple-input, multiple-output (MIMO) antennas . The 802.11n standard allows for up to four antennas, which can handle up to 4 simultaneous data streams. Typically, the number of antennas is described in the technical specifications as 4x4, 3x3, and so on depending on the number of antennas. But, you can't tell just by looking, you have to check the documentation. Generally speaking the more antennas, the more simultaneous Wi-Fi connections the AP can handle, and the better the overall network performance.
It's not just how many antennas you have though. Higher-end APs use techniques like beam-forming to automatically work out the best use for those multiple antennas. In fact, 'smart antennas,' like D-Link's Xtreme N ANT24-0230 Antenna, will help compatible 802.11n APs perform better.
Last, but never least, the fastest 802.11n is only as fast as its slowest link . So, for instance, if your office is still using a T1 with its 1.544Mbps no one is likely to see any significant Internet speed increase when switching from 802.11g to 802.11n.
The bottom line: While it may look like simply adding 802.11n to your network may look like a cheap and easy way to expand and speed-up your network, it's really not. You still need to plan your network in detail, use higher-end network equipment. and possibly upgrade your Internet backbone to make the most out of 802.11n's potential for higher speeds.
Still, if you do your homework, you really can get a Wi-Fi network that will answer your in-house network expansion needs while still providing close to Fast Ethernet's 100Mbps speeds. Just as long as you keep in mind that 802.11n, by itself, isn't a silver bullet for your network speed needs, you'll do fine.