Layer 2 – the Data Link Layer

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Join David for an overview of the Data Link Layer. The 802.11 Data Link Layer is divided into two sublayers:
- The upper portion is the IEEE 802.2 Logical Link (LLC) sublayer, which is identical for all 802-based networks, although it is not used by all IEEE 802 networks
- The bottom portion of the Data-Link Layer is the Media Access Control (MAC) sublayer. The 802.11 standard defines operations at the MAC sublayer.

Key Definitions:
- MAC Service Data Unit (MSDU) – contains data from the LLC and layers 3-7. MSDU is the data payload that contains the IP packet plus some LLC data.
- MAC Protocol Data Unit (MPDU) – a 802.11 frame. Consists of a MAC Header and Frame Body.
- MAC Header – frame control information, duration information, MAC addressing, sequence control, QoS control information, and HT control information are all found in the MAC Header.
- Frame Body – the frame body component can vary in size and contains information that is different depending on the frame type and frame subtype. The MSDU upper-layer payload is encapsulated in the frame body. The MSDU layer 3-7 payload is protected when using encryption.

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