Frame Types; Frame Formats; Preamble; Plcp Header - Black Box LW0050A Manual

PRO 11 SERIES WIRELESS ETHERNET
Unicast frames can also be poled by the stations at the DTIM intervals.
E.9 Frame Types
There are three main types of frames:
• Data Frames, which are used for data transmission
• Control Frames, which are used to control access to the medium (for example,
RTS, CTS, and ACK), and
• Management Frames, which are frames that are transmitted in the same
manner as data frames to exchange management information, but are not
forwarded to upper layers (for example, beacon frames).
Each frame type is subdivided into different Subtypes, according to its specific
function.
E.10 Frame Formats
All 802.11 frames are composed of the following components: Preamble, PLCP
Header, MAC Data, and CRC.
E.10.1 P
REAMBLE
This is PHY-dependent, and includes:
• Synch: An 80-bit sequence of alternating zeros and ones, which is used by the
PHY circuitry to select the appropriate antenna (if diversity is used), and to
reach steady-state frequency offset correction and synchronization with the
received packet timing.
• SFD: A Start Frame delimiter which consists of the 16-bit binary pattern 0000
1100 1011 1101, which is used to define frame timing.
E.10.2 PLCP H
EADER
The PLCP Header is always transmitted at 1 Mbps and contains logical information
used by the PHY Layer to decode the frame. It consists of:
• PLCP_PDU Length Word, which represents the number of bytes contained in
the packet. This is useful for the PHY to correctly detect the end of packet.
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NOTE