A comparison of wi-fi and wimax with case studies - Florida State ...

3.3.2.4. Fragmentation
In most occasions, the frames from the upper layer maybe longer than the fragmentation
threshold. In this situation, the frames have to be fragmented before transmitting. The advantages
for using fragmentation are that it can improve throughput and reliability. By fragmenting frames,
the interference only destroys small pieces of frames, but not the entire frames. Thus the overall
effective transmission is improved. Also, only the destroyed pieces need to be retransmitted,
therefore, the reliability is also improved.
The transmission process of fragmented frames is called fragmentation burst. In the clause,
there are no rules for fragmentation threshold. It depends on network designers. During the
transmission, each fragment has the same frame sequence number and an increasing fragment
number for recombination. To keep occupying the channel for completing fragmentation burst,
each fragment will reset the NAV for next fragment including ACK. Figure 3-18[55]. [17][55]
3.3.2.5. Interframe spacing
Figure 3-18 A Fragment Burst
Interframe spacing is a very important protocol for coordinating medium access. There are
four different intervals which are shown in figure 3-19[55]. To avoid collision, stations wait a
certain period of time until channels are idle before transmission. These different intervals decide
the priority for different types of transmission. High priority transmissions wait a shorter amount
of time, so it can occupy the channel first. [17][55]
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