In the IEEE 802.11 wireless LAN protocols (such as Wi-Fi), a MAC frame is constructed of common fields (which are present in all types of frames) and specific fields (present in certain cases, depending on the type and subtype specified in the first octet of the frame).
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 (FCS) 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.
The first three fields (Protocol Version, Type and Subtype) in the Frame Control field are always present. The fields, in their order of appearance in transmission, are:
The two-bit protocol version subfield is set to 0 for WLAN (PV0) and 1 for IEEE 802.11ah (PV1). The revision level is incremented only when there is a fundamental incompatibility between two versions of the standard. [1] [2] PV1 description is incorporated in the latest 802.11-2020 standard.
Type value (bits 3–2) | Type description | Subtype value (bits 7–4) | Subtype description |
---|---|---|---|
00 | Management | 0000 | Association Request |
00 | Management | 0001 | Association Response |
00 | Management | 0010 | Reassociation Request |
00 | Management | 0011 | Reassociation Response |
00 | Management | 0100 | Probe Request |
00 | Management | 0101 | Probe Response |
00 | Management | 0110 | Timing Advertisement |
00 | Management | 0111 | Reserved |
00 | Management | 1000 | Beacon |
00 | Management | 1001 | ATIM |
00 | Management | 1010 | Disassociation |
00 | Management | 1011 | Authentication |
00 | Management | 1100 | Deauthentication |
00 | Management | 1101 | Action |
00 | Management | 1110 | Action No Ack (NACK) |
00 | Management | 1111 | Reserved |
01 | Control | 0000–0001 | Reserved |
01 | Control | 0010 | Trigger [3] |
01 | Control | 0011 | TACK |
01 | Control | 0100 | Beamforming Report Poll |
01 | Control | 0101 | VHT/HE NDP Announcement |
01 | Control | 0110 | Control Frame Extension |
01 | Control | 0111 | Control Wrapper |
01 | Control | 1000 | Block Ack Request (BAR) |
01 | Control | 1001 | Block Ack (BA) |
01 | Control | 1010 | PS-Poll |
01 | Control | 1011 | RTS |
01 | Control | 1100 | CTS |
01 | Control | 1101 | ACK |
01 | Control | 1110 | CF-End |
01 | Control | 1111 | CF-End + CF-ACK |
10 | Data | 0000 | Data |
10 | Data | 0001–0011 | Reserved |
10 | Data | 0100 | Null (no data) |
10 | Data | 0101–0111 | Reserved |
10 | Data | 1000 | QoS Data |
10 | Data | 1001 | QoS Data + CF-ACK |
10 | Data | 1010 | QoS Data + CF-Poll |
10 | Data | 1011 | QoS Data + CF-ACK + CF-Poll |
10 | Data | 1100 | QoS Null (no data) |
10 | Data | 1101 | Reserved |
10 | Data | 1110 | QoS CF-Poll (no data) |
10 | Data | 1111 | QoS CF-ACK + CF-Poll (no data) |
11 | Extension | 0000 | DMG Beacon |
11 | Extension | 0001 | S1G Beacon |
11 | Extension | 0010–1111 | Reserved |
ToDS is one bit in length and set to 1 if destined to Distribution System, [4] while FromDS is a one-bit length that is set to 1 if originated from Distribution System. [4]
Set to 1 if the Data or Management frame is part retransmission of the earlier frame. This bit is reused for different purpose in Control frame.
Set to 1 if the Management Frame is protected by encryption as described in IEEE_802.11w-2009.
It is one bit in length and is used for two purposes:
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IEEE 802.11e-2005 or 802.11e is an approved amendment to the IEEE 802.11 standard that defines a set of quality of service (QoS) enhancements for wireless LAN applications through modifications to the media access control (MAC) layer. The standard is considered of critical importance for delay-sensitive applications, such as voice over wireless LAN and streaming multimedia. The amendment has been incorporated into the published IEEE 802.11-2007 standard.
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Counter Mode Cipher Block Chaining Message Authentication Code Protocol or CCM mode Protocol (CCMP) is an encryption protocol designed for Wireless LAN products that implements the standards of the IEEE 802.11i amendment to the original IEEE 802.11 standard. CCMP is an enhanced data cryptographic encapsulation mechanism designed for data confidentiality and based upon the Counter Mode with CBC-MAC of the Advanced Encryption Standard (AES) standard. It was created to address the vulnerabilities presented by Wired Equivalent Privacy (WEP), a dated, insecure protocol.
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. In an infrastructurebasic service set (BSS), beacon frames are transmitted by the access point (AP). In ad hoc (IBSS) networks, beacon generation is distributed among the stations. For the 2.4 GHz spectrum, when having more than 15 SSIDs on non-overlapping channels, beacon frames start to consume significant amount of air time and degrade performance even when most of the networks are idle.
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Block acknowledgement (BA) was initially defined in IEEE 802.11e as an optional scheme to improve the MAC efficiency. 802.11n amendment ratified in 2009 enhances this BA mechanism then made it as mandatory to support by all 802.11n-capable devices.
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Traffic indication map (TIM) is a structure used in 802.11 wireless network management frames.
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In a WLAN, packets can be a stream of video, voice, or data, which each have different priorities to be served by an access point. The Traffic Identifier (TID) is an identifier used to classify a packet in Wireless LANs. When a base station receives an 802.11 frame with the TID set for audio, for example, the priority given is higher than a data frame.
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