802.11a Packet Formats
What is the general structure of an 802.11a packet?
An 802.11a packet consists of a preamble, header, payload (data), and frame check sequence (FCS).
What types of frames exist in 802.11a?
There are three main frame types: Management, Control, and Data frames.
What is the purpose of the preamble in 802.11a packets?
The preamble allows the receiver to synchronize timing and frequency before decoding the actual data.
What modulation is used in the preamble of 802.11a?
The preamble uses BPSK modulation at 6 Mbps to ensure robust synchronization.
What is contained in the PLCP header?
The Physical Layer Convergence Protocol (PLCP) header carries information about the length and data rate of the payload.
How long is the PLCP header in 802.11a?
The PLCP header is 24 microseconds long, consisting of SIGNAL, SERVICE, LENGTH, and CRC fields.
What does the SIGNAL field specify in the PLCP header?
It indicates the data rate at which the payload is transmitted.
What is the purpose of the SERVICE field in the PLCP header?
It carries information about additional features or future use, usually set to zero in 802.11a.
What does the LENGTH field represent in the PLCP header?
The LENGTH field specifies the number of microseconds the payload transmission will last.
What is the role of the CRC in the PLCP header?
The CRC checks the integrity of the PLCP header to ensure it is received correctly.
What is the MAC header in 802.11a packets?
The MAC header contains frame control, duration, address fields, sequence control, and QoS control if used.
How many address fields does the MAC header have?
Typically, there are up to four address fields, depending on the frame type and whether it is infrastructure or ad hoc mode.
What is the Frame Control field in the MAC header?
It defines the frame type, subtype, protocol version, and control flags like retry, power management, and more.
What does the Duration/ID field indicate?
It contains the time in microseconds the channel will be reserved for the transmission or contains association ID for power management.
What is the Sequence Control field used for?
It helps in detecting duplicate frames and ordering frames correctly via sequence numbers.
What is the purpose of the Frame Body (payload)?
It carries the actual data or management/control information being transmitted.
What is the Frame Check Sequence (FCS)?
A 32-bit CRC used to detect errors in the entire MAC frame.
How does 802.11a packet format support high data rates?
Through the use of OFDM modulation, variable data rates in the SIGNAL field, and efficient MAC framing.
Are management and control frames formatted differently from data frames?
Yes, management and control frames have specific frame bodies and may omit some MAC header fields for efficiency.
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