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The very first two octets transmitted by a station are the Frame Control. The first three subfields within the frame control and the last field are always present in all types of 802.11 frames. These three subfields consist of two bits Protocol Version subfield, two bits Type subfield, and four bits Subtype subfield.
802.11 Beacon frame. A beacon frame is a type of management frame in IEEE 802.11 WLANs. It contains information about the network. Beacon frames are transmitted periodically; they serve to announce the presence of a wireless LAN and to provide a timing signal to synchronise communications with the devices using the network (the members of a service set).
The Sequence Control field is a two-byte section used to identify message order and eliminate duplicate frames. The first 4 bits are used for the fragmentation number, and the last 12 bits are the sequence number. An optional two-byte Quality of Service control field, present in QoS Data frames; it was added with 802.11e.
The Protected Frame field is set to 0 in all other frames. When the bit Protected Frame field is set to 1 in a data frame, the Frame Body field is protected utilizing the cryptographic encapsulation algorithm and expanded as defined in Clause 8. Only WEP is allowed as the cryptographic encapsulation algorithm for management frames of subtype ...
The TID subfield sits in certain MAC frames. The presence of TID, and thus the presence of QoS, is determined by the value set in the MSB of the subtype field (bit b7) of the Frame Control field. A QoS-enabled 802.11 header uses the TID to classify and prioritize processing of incoming or outgoing frames.
IEEE 802.11 RTS/CTS (request to send/clear to send) is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem. Originally the protocol fixed the exposed node problem as well, but later RTS/CTS does not, but includes ACKs.
Every frame transmitted by an 802.11 device has a significant amount of overhead, including radio level headers, media access control (MAC) frame fields, inter-frame spacing, and acknowledgement of transmitted frames. At the highest data rates, this overhead can consume more bandwidth than the payload data frame. [1]
Following a beacon frame that includes a DTIM, the access point will release the buffered broadcast and multicast data, if any exists. Since beacon frames are sent using the mandatory 802.11 algorithm for carrier-sense multiple access with collision avoidance (CSMA/CA), the access point must wait if a client device is sending a frame when the ...