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Monday, March 31, 2008, 05:00 am PT (08:00 am ET)

Exploring Time Capsule: WiFi 802.11n and the 5GHz band

Earlier versions of the WiFi specification all used the 2.4GHz radio spectrum. The new 802.11n standard, supported in Time Capsule, the square AirPort Extreme, and recently shipping AirPort Express units, allows users to alternatively select the use of 5GHz channels. This segment, the third of six, compares the pros and cons of using this new section of frequencies, which can be both problematic and provide a major boost in speed.

Our real world testing of Time Capsule's WiFi performance suggested two findings. First, wireless networking performance can and will vary all over the map even without any obvious variables changing. This makes it difficult to accurately profile the speed of a wireless configuration. In comparison, file copy times over Ethernet or direct connections such as USB were easy to verify in additional follow-up tests. Actual results for wireless throughput will vary dramatically in relation to obvious sources of radio interference in addition to other sporadic factors that are harder to identify.

Second, users with multiple base stations should ideally connect the computers that will be making heavy use of file sharing to the base station actually hosting the shared drive. This requires some network planning, as client computers will attempt to connect to the base station supplying the strongest signal of all the base stations that are on the same network. In other words, locate the Time Capsule or AirPort Extreme hosting the share drive closest to the systems that will be using it the most, and use any additional base stations to extend the network signal elsewhere.

Next, evaluate the wireless network signal strength within AirPort Utility (below) to make sure there are no obvious sources of signal interference. This could include radio emitting devices such as cordless phones and microwave ovens, unnecessary Bluetooth devices that could be turned off, and any metal barriers that might obstruct the signal. Neighboring WiFi networks may also likely impede ideal connectivity, so if possible, experiment with different WiFi channel settings to situate your wireless network outside of the signal range used by other nearby networks.

Time Capsule


802.11n WiFi and The 5 GHz Band

As noted earlier, with WiFi 802.11n on the AirPort Extreme and Time Capsule, you can set up your network to use a different set of frequencies all together by selecting "802.11n only (5GHz)" as the radio mode in Wireless settings (below). This isolates your network from interference from other 802.11b/g WiFi networks as well as any 2.5 GHz cordless phones, but of course prevents older 802.11b/g clients from connecting to your network, including most Macs earlier than 2007 and other WiFi b/g devices such as the iPhone or iPod Touch.

Time Capsule


If you have both old and new wireless devices, you can cable (via Ethernet, below) a new 802.11n base station hosting a 5 GHz network to an older 802.11b/g base station configured to operate in the "802.11b/g compatible" 2.4 GHz band. This enables faster devices to connect at full speed with minimal interference, while also allowing older devices to connect to the same network through the older base station and interoperate together with every other device on the same network. This setup also prevents 802.11b/g devices from temporarily slowing down a 802.11n network as they transmit, which happens when using mixed devices on a 802.11n base station configured as "b/g compatible."

Time Capsule


Incidentally, there is also an 802.11a standard, which is essentially 802.11g running in the 5 GHz band. All of Apple's 802.11n base stations and wireless cards now backwardly support 802.11a/b/g, but Apple never directly supported the earlier 802.11a standard in its products prior to 802.11n because 802.11a was largely intended for office deployments, where the downsides to the 5 GHz band could be more easily worked around. Which brings us to the potential drawbacks—and advantages—of using 5 GHz.

On Page 2 of 2: The Pros and Cons of 5 GHz; Use Wide Channels For a Big Boost.