Achieving blanket WLAN coverage on a university campus

I read in quite a few articles that the university campuses are completely covered by WLANs. How is this achieved? Each department may have a different WLAN network. How are these WLANs interconnected?

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Blanket wireless coverage of a campus is usually accomplished by placing many access points throughout the coverage area, connecting each AP by Ethernet to the same wired network (campus LAN). For example, each AP may be connected by Ethernet to a local Ethernet switch for the floor or building. VLAN tags are sometimes used to treat all wireless traffic as though it were one large subnet.

Alternatively, each group of APs can be connected (by Ethernet) to the building's wireless gateway or switch. All gateways/switches will then be connected to each other by the wired network. The advantage of this topology is that the wireless gateway or switch can control, monitor, and log wireless user access to the campus LAN. Most wireless gateways and switches include mobility features that can also help stations roam from one subnet to another without interruption.

For blanket coverage, all participating APs are given the same SSID and treated as part of the same WLAN. Users can often roam freely between APs and reach the same destinations no matter which AP they are currently associated through. Of course, it's also possible to create a number of separate WLANs, where each WLAN has a different SSID and perhaps only allows connections from a certain subset of users. Some APs can support multiple SSIDs, effectively creating multiple logical WLANs from one physical AP. Deciding this is part of network design, and reflects what the network operator is trying to accomplish. For example, a university might create separate SSIDs for the faculty WLAN and the student WLAN, applying different access rules to each of these WLANs.

This was first published in December 2003

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