An 802.11 frame encapsulates a Layer 3 packet for transmission over the air. Its format differs from Ethernet because wireless communication through an access point can require additional addressing information. section 19.1 section 19.1.1
Read the address fields according to each frame’s role:
- BSSID identifies the access point; the destination address identifies the final recipient. section 19.1.1
- Source address identifies the original sender; receiver address identifies the immediate recipient. section 19.1.1
- Transmitter address identifies the immediate sender, and a frame can contain one to four address fields depending on its message type. section 19.1.1
- 802.11 defines management, control, and data frames; data frames carry network data, while management and control frames support wireless communication. section 19.3
Forwarding through an access point
When PC1 sends a frame to PC2 through AP1, PC1 identifies AP1 as the immediate recipient and PC2 as the final recipient. The receiver and BSSID can therefore refer to the same AP address. section 19.1.1
Figure 19.1 The 802.11 frame format. Field sizes in bytes are indicated above each field. Depending on the 802.11 standard being used and the message type, some of the fields might not be present in the frame.
Use the frame-format figure to inspect field order, field sizes, and fields that may be absent for particular standards or message types. section 19.1.1
