New AirPort, old network

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Apple’s new AirPort Extreme Base Station, based on the still-in-progress IEEE 802.11n standard, can wirelessly transmit more than 90 megabits per second (Mbps) of data. The previous generation of AirPort Extreme (which relied on the older, 802.11g standard) typically reached between 20 and 30 Mbps.

Unfortunately, when you mix one of those new base stations—or a Mac that supports 802.11n or an Apple TV—with hardware that supports 802.11g or the (even earlier) 802.11b standard, those older devices will slow down the entire network. Given that many of us have such legacy hardware, what’s the best way to mix the old with the new?

The trick is to set up two entirely separate wireless networks, in which you keep the faster, 802.11n-based segments apart from segments that go slower. That way, you get the best performance from each. Here’s how to create one such network setup; you can adapt these instructions to your particular equipment and needs.

Bands and bandwidth

To understand how this setup works, you have to understand that 802.11n has access to a range of radio frequencies not available to 802.11b or 802.11g.

Wireless devices are designed to use specific ranges of frequencies called channels; those channels, in turn, are located within larger-spectrum ranges called bands. Most Wi-Fi equipment—802.11b, 802.11g, and 802.11n—can work in the 2.4GHz band. (In this context, the gigahertz doesn’t refer to speed or bandwidth; rather, it refers to points on the electromagnetic spectrum.) That band is crowded: microwave ovens, cordless phones, Bluetooth devices, cameras, and baby monitors, as well as Wi-Fi networks, all compete for slices of it. But 802.11n can also use the 5GHz band, which is both large and underused.

At this writing, Apple supports eight out of 23 possible clear channels (nonoverlapping frequency ranges) in the 5GHz band; 2.4GHz Wi-Fi offers just three. I expect that Apple will upgrade the new AirPort Base Stations to handle even more 5GHz channels.

Set up the slow segment

So let’s say you have a new AirPort Extreme gateway; an older, 802.11g base station; a mix of Macs (some using 802.11n, and others using 802.11b or 802.11g); and a broadband modem.

The new AirPort gateway will serve as the gateway and controller for the network as a whole. The 802.11g base station will only pass networking traffic to and from the older Macs.

After connecting your 802.11g base station to one of your Macs (wirelessly or via Ethernet), launch the copy of the latest AirPort Utility (which came with your new AirPort Extreme Base Station). Select the older base station in the list on the left, and then choose Manual Setup (1-L). Click on the AirPort button and select the Wireless tab. Change the network name to something like Home 2.4 GHz or anything else that’ll remind you it’s the older of the two networks you’re configuring. Next, click on the Internet button and select Using DHCP from the Configure IPv4 pop-up menu. Select Off from the Connection Sharing pop-up menu. (This allows the 802.11n base station to provide network addresses for computers that connect to it via both Wi-Fi and Ethernet, as well as those that connect via Wi-Fi to the 802.11g base station.) Click on Update to make the base station restart with the new settings.

That done, run an Ethernet cable from the 802.11g base station’s WAN port (it looks like a circle of dots) to any of the LAN ports on the 802.11n base station.

Set up the fast network

Now it’s time to set up the zippy section of your network with a 2007-era AirPort Extreme Base Station. (I’ll leave out the various security and other options you might also want to set.)

Launch AirPort Utility; select your newer, 802.11n base station; and switch to Manual Setup (1-L). Click on the AirPort button and select the Wireless tab. Enter a unique and descriptive name in the Network Name field, such as Home 5 GHz. Select 802.11n Only (5 GHz) from the Radio Mode pop-up menu. Click on the Wireless Options button and select Use Wide Channels. (This option is available only in certain countries, including the United States.) Click on the Internet button and make sure Connection Sharing is set to Share A Public IP Address. To finish, click on Update to restart the base station.

Hook it up

You can now connect your Macs and Apple TVs to their respective base stations, using the menu bar’s AirPort drop-down menu. All Intel Core 2 Duo models (except the 1.83GHz 17-inch iMac) qualify, as does the Mac Pro with the Wi-Fi option. Apple TVs can browse networks to connect to, so make sure you select your 5GHz network for that hardware, too. Connect any older 802.11b or 802.11g equipment to the 2.4GHz network.

This new mixed network should give you the best possible speed, compatibility, and interoperability, without requiring that you rebuild your network—all you have to do is extend it up the electromagnetic spectrum.

[ Glenn Fleishman wrote the e-book Take Control of Your 802.11n AirPort Extreme Network (2007) and edits Wi-Fi Networking News. ]

Base Station Management: Using the AirPort Utility that came with your new AirPort Extreme Base Station, you can manage all the base stations in your network.
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