In your 21st-century office, employees carry laptops and cell phones. They want to move from office to neighboring office to conference room at will, and access the Internet as well as your internal network wherever they happen to be. You know you need a wireless office. But what exactly does it take to create one?

First, let's dispense with some confusing terminology: a wireless router connects directly to the Internet and broadcasts the signal by radio wave. Wireless devices that connect to your wired network and thus provide Internet access throughout your office are access points. But if you look for "wireless access points," at your local electronics store, you may not find them.

"A router can act as an access point, but an access point can't act as a router," explains Mark Newland, vice president of the hosting and IT consultation division of SGW Integrated Marketing Communications. Since both are equally inexpensive, most home and small-office users simply buy a router when they need either one.

Okay, so how many access points do you need for a wireless office? Here are some steps that can help you figure it out.

Consider your space

Most readily available wireless access points can send a signal up to 300 feet indoors, if nothing interrupts it. But many factors can reduce that range. Walls, especially of brick, concrete or stone, metal or piping of any kind, plants, people and many other things will degrade or even completely block the signal. "Even a heavy-duty file cabinet can interfere with a signal, and refrigerators are notorious," Newland says.

So to be safe, networking professionals assume a wireless signal will reach 100 to 150 feet. This means a single access point can give wireless coverage to a circle of 200 to 300 feet in diameter, o -- if you remember high-school math -- about 31,400 square feet.

To cut down on signal blockage, putting a wireless access point in a corner, on a shelf, under a desk, or anywhere else it's likely to be obstructed is a bad idea. Try to have the router out in the open, and place it as near as you can to the center of the space you're trying to cover. A very rough estimate is that, in a typical office cubicle configuration, one wireless access point can cover about five to ten work spaces. At SGW, Newland says, four wireless access points provide wi-fi for about 45 employees in offices on two different floors. The company uses two access points per floor, even though one space is three times larger than the other.

"Our 18,000-square-foot space is basically one big square, and there aren't many obstructions, so two are sufficient," he says. "Our second floor is 6,000 square feet, but has some concrete barriers."

If you're lucky, one router may be able to supply wi-fi on more than one level of your location. This is because most Wi-Fi antennas are "omnidirectional" which means they send out their signal not in a circle, but in a sphere. "You need pretty strong antennas, and it depends on the sub-structure between the floors," says Mark A. Gilmore, president and cofounder of Wired Integrations. "But it can happen. I worked with a law firm where people were able to catch the wireless signal between two floors."

Set your channels correctly

Access points have a range of frequencies, or channels, that they can use to broadcast a wireless signal. "There are 11 channels in the standard consumer level routers and they default to channel 6," Newland notes. To avoid having them interfere with each other, he usually sets one device on channel 1 and the other on channel 11. If a third device is needed within an office space, he sets it at 7 or 5.

Do the laptop test

Although there is software that helps model a wireless network design, it doesn't really make sense for small offices. "The easiest way to test is to hook up an access point, put it in a conference room, fire up a laptop and start wandering around the office," Gilmore says. "That's how we experts do it. You might hit a dead spot where you least expect it."

Set a single SSID and strong password

Every wireless router or access point has two identities: the actual name of the device and its SSID (service set identifier) which in effect is the name of the signal it broadcasts. When setting up your wireless network, you want to give each access point device its own name (Access Point 1, Access Point 2, etc.), but have them all broadcast the same SSID and use the same strong password. Using a single SSID has many advantages. For one thing, when users move from place to place, they won't have to sign back in to the network. For another, it allows you to have stronger security. Since your device's password should be long and hard to guess (in other words, not something like 1234567890) it will be hard for employees to remember, so you don't want them to have to input the password repeatedly. Newland recommends taking security one step further by setting the SSID as "hidden" so it won't show up on lists of available networks

Give guests a network of their own

Speaking of guests, how do you deal with the inevitable vendor or consultant who needs wireless Internet access at your location? One cheap and easy way to do this is to outsource your guest wireless (see article). Another is to buy a cellular wireless router that can provide Internet access via a mobile network, such as Verizon or Sprint. A third option is to create an entirely separate network for guests, ideally with its own Internet connection.

Whatever you do, keep in mind that your office's wireless network connects to your company's own network. Only your employees get access to tha -- and they should be happily roaming the halls, laptops in hand, in no time.