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From the CWAP official study guide, a question reads:

The information found inside an IP packet is considered the main payload for which of the following?

A. MPDU
B. PPDU
C. PSDU
D. MSDU
E. MMPD

I chose A (MPDU). However, the book says the correct answer is D (MSDU) with the following explanation:

An IP packet comprises layer 3-7 information. The MAC Service Data Unit (MSDU) contains data from the LLC sublayer and/or any number of layers above the Data-Link layer. The MSDU is the payload found inside the body of 802.11 data frames.

However, the IP packet is not the payload for the MSDU, because the MSDU itself is the payload, right? The IP packet is the MSDU, which are both payloads for the MPDU.

Was the wording of the question misleading, or am I missing somewhere here?

Hi Elin05,

The MSDU is the IP packet plus the LLC data.  The LLC is the upper portion of the Data-Link Layer.  The bottom portion of the Data-Link Layer is the MAC sub layer which is know as the MPDU.  So as the IP packet is passed down to layer 2 of the OSI model it adds the LLC (logical link control) and is identified as the MAC Service Data Unit. then it pass down to the bottom portion of the Data-link layer it identified as MAC protocol Data Unit (MPDU) which is closet to the Physical layer.  So the MSDU is the payload of the MPDU.  The way I remember is the P is MPDU is closet to the physical layer.