E-DOC-CTC-20060609-0001 v2.0
Chapter 6
Virtual Access Points
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Emulation of physical APs
In order to provide wireless stations with the impression of multiple physical APs within the same area, a
virtual AP must emulate the operation of a physical AP. A virtual AP implementation can approximate the
behaviour of a physical AP to a greater or lesser degree.
> Physical layer: emulating the operation of a physical AP at the physical layer is a cost compromise,
whereby the virtual APs share a common radio. As a result, virtual APs operate on a shared channel,
sharing the available bandwidth.
> MAC layer: virtual APs emulate the operation of a physical AP by the use of multiple SSIDs, multiple
BSSIDs and multiple sets of capabilities.
Examples
The following examples illustrate the use of virtual APs in a residential environment:
> Separation of users: the owner of an AP may want to separate guests from members of the family. To this
end, the AP advertises two service networks by sending beacon frames with different SSIDs. One virtual
AP can advertise the SSID “MyGuest“, offering guests access to the Internet (i.e. the guest network).
Another virtual AP can advertise the SSID “MyNet“, offering members of the family access to the home
network. If the key to access the guest network is compromised, this key can be easily changed, while the
members of the family do not need to change the key used to access the home network.
> Separation of services: the owner of an AP may want to separate the access to base services, e.g. TV and
Internet, from the access to a specific service, e.g. a wellness delivery kiosk service. To this end, the AP
advertises two service networks by sending beacon frames with different SSIDs. One virtual AP can
advertise the SSID “MyBase“, offering all users access to base services. Another virtual AP can advertise
the SSID “MyWell“, offering service specific stations access to the wellness delivery kiosk service, e.g. to
order the hairdresser, choose from next day’s menu or view the medication plan.
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