WiFi protocol stack

The WLAN or WiFi related protocols are in the data-link and physical layer of the OSI layered reference model. The Logical Link Control (LLC) part of the data link layer is implemented in software whereas the media access control (MAC) part of the data-link layer is implemented in hardware. This is a typical configuration in most computing devices. However, on a smaller form factor device, progressively different parts of the functions are built into hardware or is resident on the WiFi chip.

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When a device intends to connect to a specific WiFi network through an access point, the user/device is authenticated by the access point. The authentication process – obtaining the login id, password, etc. is executed by a program termed the “supplicant”. The supplicant assists in the interaction whereas the verification and the association are done by the MAC Sublayer Management Entity (MLME).

Depending upon the implementation of the MLME in hardware or software, the implementation is termed as a “FullMac” or a “SoftMac”. This distinction is important to understand what functions are on the attack surface. With the arrival of IoT and the need for WiFi in a class of IoT devices, the upper layers are progressively implemented on hardware leading to the two combinations – “FullMAC + Supplicant + TCP/IP, and FullMAC + Supplicant + TCP/IP + Applications”.

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