Single Access Point and Multiple SSIDs

It is possible for a single access point to have multiple SSIDs. This capability is more common in enterprise class access points and is usually implemented so that each SSID has a separate BSSID (MAC address). Each SSID can be hidden or in clear text or a combination. Some vendors allow as many as 32 different virtual WLANs to be configured per access point radio.

The most common multiple SSID configuration is two SSIDs, a guest network for visitors that provides Internet access only and a private wireless LAN that is connected to company resources.

Enterprise Class Access Points and Multiple SSIDs

Virtually all enterprise access points support multiple SSIDs per access point radio. Analogous to using VLANs in switches to segment users, multiple SSIDs create virtual APs that can be used to segment wireless users. In most cases each virtual access point is associated to a different wired VLAN.

SOHO Access Points/Wireless Broadband Routers and Multiple SSIDs

Most low end access points/wireless routers ship with a single radio and single configurable SSID. Several third party firmware packages exist that expand the features of these wireless broadband routers to add multiple SSID support in addition to many other enterprise class features such as radius support.

Some of the more popular third party firmware distributions are DD-WRT and OpenWRT. Both OpenWRT and DD-WRT support the Linksys, Netgear, and D-Link products.

Other combinations of access points and SSIDs are below.

No Access Point and No SSID

It may sound impossible to some, but you can have a wireless network without an access point or SSID. There are many proprietary wireless networking technologies and standardized technologies such as Bluetooth or IrDA don’t utilize SSIDs or access points.

No Access Point and Single SSID

Another name for this type of network is Ad-Hoc or an IBSS (independent basis service set). In this mode two or more stations using the same SSID can communicate with each other without going through an access point or wired network.

Single Access Point and No SSID

This scenario is not possible in IEEE 802.11 compliant wireless networks. While you can “hide” a SSID by not broadcasting it in beacon frames, the SSID still exists and must exist per IEEE 802.11.

There are some 802.11 WDS (wireless distribution service) configurations that don’t utilize SSIDs and don’t behave like access points but in general most access points that can be used for WDS are also APs and use SSIDs to service stations. Since WDS is not a WiFi certified 802.11 mode of operation not all vendors implement this mode the same way.

Single Access Point and Single SSID

This setup is the most common and is what every access point supports. Access points that are residential class wireless broadband routers with a single wireless radio are usually limited to a single SSID. In almost all cases, the radio can support multiple SSIDs but the firmware supplied by the vendors only allows a single SSID to be configured.

Multiple Access Points and Single SSID

A single access point covers a limited area and to increase coverage requires using multiple access points that are connected together via a wired or wireless network. This type of wireless network is called and extended service set (ESS). Sharing a common SSID, in addition to covering larger area, allows for mobility by roaming different access points in the ESS.

It is common to have multiple wireless networks in the same area and the SSID provides stations an easy method to distinguish wireless networks. Extended Service Set (ESS) or multiple access points with the same SSID that are connected together via a wired network allows for larger coverage and roaming.

Multiple Access Points and Multiple SSIDs

802.11 uses unlicensed frequencies and allows anyone can setup a WLAN without notifying frequency managers or other users. 802.11 accommodate scenarios where many access points or wireless networks exist in the same area with different SSIDs. These ESS, BSS, IBSS networks share the same RF space but are not connected to each other via the same distribution system.

It is best to conduct a site survey to determine if there are other wireless LANs in existence and try to design around existing networks when possible. Technically they could all use the same SSID and channels but it is good etiquette and design to select a SSID and channel that isn’t being used already.

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Filed under: WLAN Design