Frame fragmentation is a technique used in wireless networks, specifically 802.11 (Wi-Fi), to improve the reliability of data transmission under challenging conditions.
Understanding Frame Fragmentation
In essence, frame fragmentation is the process of breaking down a large data frame into several smaller parts, called fragments, before sending them over the wireless medium. Instead of attempting to send one large chunk of data that might be lost entirely due to a single error, the data is divided into smaller, more manageable pieces.
Why Use Fragmentation?
According to the provided information, the process of fragmentation is used to improve the performance of 802.11 networks in situations where there is interference, noise, or long distances between nodes.
- Interference & Noise: Radio signals can be affected by other devices or environmental noise. A large frame is more likely to encounter an error caused by interference or noise during its transmission. If even one bit in the large frame is corrupted, the entire frame is typically considered lost and needs to be retransmitted.
- Long Distances: As the distance between a Wi-Fi client and access point increases, the signal strength decreases, making the connection more susceptible to errors.
- Increased Probability of Success: By dividing a large frame into smaller fragments, each fragment is sent individually. The probability of a single, smaller fragment being successfully transmitted without error is higher than that of a larger frame.
How It Works
When fragmentation is enabled and a frame exceeds a certain size threshold (the fragmentation threshold), the network interface card (NIC) or access point divides the frame into fragments. Each fragment is then sent as an independent data unit, complete with its own header and checksum, requiring individual acknowledgment from the receiver.
- Sending: The transmitter sends the fragments sequentially.
- Receiving: The receiver acknowledges each fragment upon successful reception.
- Retransmission: If a fragment is lost or corrupted, only that specific fragment needs to be retransmitted, rather than the entire original frame.
- Reassembly: Once all fragments of the original frame are successfully received and acknowledged, the receiver reassembles them into the original data frame.
Benefits of Fragmentation
Using fragmentation primarily offers the following advantages:
- Improved Reliability: Reduces the amount of data that needs to be retransmitted when errors occur, as only damaged fragments are resent.
- Better Performance in Impaired Conditions: Significantly improves throughput and latency in environments with high interference, noise, or weak signals due to distance.
- Reduced Airtime Usage on Retransmission: Retransmitting a small fragment uses less airtime than retransmitting a large frame, freeing up the medium faster for other devices.
While fragmentation can be beneficial in poor wireless conditions, it also adds overhead (due to extra headers and acknowledgments for each fragment) and is generally not needed or recommended in stable, high-signal environments.
