WLAN: Fragmentation

Fragmentation is a mechanism to split a big chunk into two or more small chunks. In WLAN, Max Frame size is 2346 bytes and they are typically fragmented at smaller frame (e.g, 1516 bytes).

Why we need this kind of fragmentation ?

There can be many different reasons depending on situation. In WLAN, if the packet size is too big, it would increase the probablity of collision. So reducing the probability of collision can be a good motivation for fragmentation.

Then wouldn't there be any downside (disadvantage) of the fragmentation ?

There IS downside. As I explained in CSMA/CA, for each frame the device has to go through the process of collision detection which introduce a lot of overhead. Fragmentation increase the number of frames and increased number of frame cause increased overhead.

In most case, user can configure the fragmentation size for an Access point by the AP configuration consol.