All about wireless networking and NMS/EMS

Beacon frame  is one of the management frames in  IEEE 802.11  based WLANs. It contains all the information about the network. Beacon frames are transmitted periodically, they serve to announce the presence of a wireless LAN and to synchronise the members of the service set. Beacon frames are transmitted by the  access point  (AP) in an infrastructure  basic service set  (BSS). In IBSS network beacon generation is distributed among the stations. Beacons are sent periodically at a time called Target Beacon Transmission Time(TBTT) 1 TU = 1024 microseconds Beacon interval =100 TU (100x 1024 microseconds or 102.4 milliseconds) 1. Timestamp (8 byte) 2. Beacon Interval (2 byte) 3. Capability info (2 byte) 4. SSID (variable size) 5. Supported Rates (variable size) Probe Request:  A station or client becomes active or on a PC when the wlan card it enabled it becomes active sends a probe request frame when it needs to obtain information from another station or access point.

There are 3 types of frames used in the 802.11 MAC layer 2 communications happening over the air which manages and controls the wireless link. They are Management Frames, Control Frames and Data frames.  Management Frame: 1)     Authentication frame 2)     Deauthentication frame 3)     Association request frame 4)     Association response frame 5)     Reassociation request frame 6)     Reassociation response frame 7)     Disassociation frame 8)     Beacon frame 9)     Probe request frame 10) Probe response frame Control Frames: 802.11 control frames assist in the delivery of data frames between stations. The following are common 802.11 control frame subtypes: ·           Request to Send (RTS)/Clear to Send(CTS) frame : The RTS/CTS function is optional and reduces frame collisions present when hidden stations have associations with the same access point. A station sends a RTS frame to another station as the first phase of a two-way handshake nec

The Access points continuously sends out Beacon Frames which are picked up by the nearby wlan clients. The client can also broadcast on its own probe request frame on every channel Access points within range respond with a probe response frame The client decides which access point (AP) is the best for access and sends an authentication request The access point will send an authentication reply Upon successful authentication, the client will send an association request frame to the access point The access point will reply with an association response The client is now able to pass traffic to the access point