In a closed system WLAN, which frames do not advertise the network's SSID?

• A. Beacons
• B. Data frames
• C. Probes
• D. Association frames

Answer: (A)

In WLANs, the network name (SSID) is carried in specific management frames that help devices discover and join networks. Beacons are the frames APs periodically transmit to announce the BSS and its parameters. In a hidden (closed) network, the SSID element in those beacon frames is suppressed or set to zero length, so the network name is not advertised in beacons. That makes beacon frames the ones that do not reveal the SSID in a closed system.

Other frames involved in discovering or joining networks still reveal or reference the SSID in some way: probe responses and association frames carry the SSID as part of the information exchange when a client is trying to discover or connect, and data frames do not carry SSID information at all because they are just carrying user data, not network discovery information.