How to discover which is the protocol in the 802.11 body frame?

Question

I would like to know how to discover which is the network protocol in the 802.11 body frame, I mean, for example, the ethernet frame has the field "type", but in the 802.11 standard and I didn't find any field to show me which is the protocol.

Answer 1

First, you need to look at the type field in the 802.11 header. There are three frame types - Management frames, Control frames, and Data frames.

For Data frames, the 802.11 header is followed by an 802.2 header, which contains a Destination Service Access Point (DSAP) that can specify the protocol running atop 802.11+802.2. If the DSAP and Source Service Access Point, or SSAP are both 0xAA, the 802.2 header is followed by a Subnetwork Access Protocol (SNAP) header, which contains an IEEE Organizationally Unique Identifier (OUI) field and a "protocol ID" (PID) field. The interpretation of the PID field depends on the value of the OUI field; if the OUI is 00:00:00, the PID field is an Ethernet type field, otherwise it's a value specified by the organization to which the OUI refers.