Based on the provided information, the subfields specifically highlighted within the Frame Control field as always present are the Protocol Version, Type, and Subtype.
Understanding the Frame Control Field
The Frame Control field is a critical part of the 802.11 (Wi-Fi) frame header. It's the very first field and is 16 bits long. Its various subfields determine the type of frame being transmitted, its function, and other control information necessary for processing the frame correctly within the wireless network.
The provided reference highlights specific subfields within the Frame Control field that are consistently found in all 802.11 frame types. These are the initial subfields and are fundamental to frame identification and handling.
Key Subfields of Frame Control (as per reference)
The reference specifically mentions the first three subfields within the Frame Control field which are always present. These define the fundamental nature of the 802.11 frame.
Here are the subfields detailed:
- Protocol Version: This subfield indicates the version of the 802.11 protocol used.
- Size: 2 bits
- Function: Identifies the 802.11 standard version (e.g., 0 for current versions).
- Type: This subfield categorizes the general function of the 802.11 frame. There are three main types: Management, Control, and Data.
- Size: 2 bits
- Function: Specifies if the frame is for network management, control operations, or data transmission.
- Subtype: This subfield provides further classification within a given Type. For example, Management frames have subtypes like Beacon, Probe Request, and Association Request, while Control frames have subtypes like ACK and RTS.
- Size: 4 bits
- Function: Pinpoints the specific purpose of the frame within its Type category.
Together, the Type and Subtype subfields determine the exact function of the 802.11 frame (e.g., a Management frame with the Subtype "Beacon" is a Beacon frame).
Summary Table
| Subfield | Size (Bits) | Description |
|---|---|---|
| Protocol Version | 2 | Specifies the 802.11 protocol version. |
| Type | 2 | Categorizes the frame (Management, Control, Data). |
| Subtype | 4 | Defines the specific function within the Type. |
These three subfields, Protocol Version (2 bits), Type (2 bits), and Subtype (4 bits), are the initial components of the Frame Control field and are always present in all types of 802.11 frames, as noted in the provided information.
