Wireless Network Administration: Roaming

You can use two or more wireless access points (WAP) to create a large wireless network in which computer users can roam from area to area and still be connected to the wireless network. As the user moves out of the range of one access point, another access point automatically picks up the user and takes over without interrupting the user’s network service.

To set up two or more access points for roaming, you must carefully place the WAPs so that all areas of the office or building that are being networked are in range of at least one of the WAPs. Then, just make sure that all the computers and access points use the same SSID and channel.

Two or more access points joined for the purposes of roaming, along with all the wireless computers connected to any of the access points, form what’s called an Extended Service Set, or ESS. The access points in the ESS are usually connected to a wired network.

One of the current limitations of roaming is that each access point in an ESS must be on the same TCP/IP subnet. That way, a computer that roams from one access point to another within the ESS retains the same IP address. If the access points had a different subnet, a roaming computer would have to change IP addresses when it moved from one access point to another.

Wireless bridging

Another use for wireless access points is to bridge separate subnets that can’t easily be connected by cable. For example, suppose that you have two office buildings that are only about 50 feet apart. To run cable from one building to the other, you’d have to bury conduit — a potentially expensive job.

Because the buildings are so close, though, you can probably connect them with a pair of wireless access points that function as a wireless bridge between the two networks. Connect one of the access points to the first network and the other access point to the second network. Then, configure both access points to use the same SSID and channel.

Ad-hoc networks

A wireless access point is not necessary to set up a wireless network. Any time two or more wireless devices come within range of each other, they can link up to form an ad-hoc network. For example, if you and a few of your friends all have notebook computers with 802.11b/g wireless network adapters, you can meet anywhere and form an ad-hoc network.

All of the computers within range of each other in an ad-hoc network are called an Independent Basic Service Set, or IBSS.