An extended service set, consisting of a set of BSSs, must have a common service set identifier (SSID). The BSSs can all work on the same or different channels. This helps to boost the signal throughout the wireless network.
A single service set consists of all STAs receiving signals from a given AP and creates an 802.11 wireless LAN (WLAN). Each STA may receive a signal from several APs within their range. Depending on its configuration each STA can, manually or automatically, select the network with which to associate. And multiple APs may share the same SSID as part of an extended service set.
Although not part of the 802.11 standard, some wireless APs may broadcast multiple SSIDs, allowing virtual access points to be created – each with their own security and network settings.The most basic BSS consists of one AP and one STA.