It is required to measure the number of re-transmission that is occurring in IEEE 802.11.
You don't specify the direction of the UDP traffic. If it is largely from server to client, then a client won't be able to accurately measure this statistic. Only the AP would have a chance to capture this information.
Why? Because a client will ACK the first 802.11 frame it understands/receives so it won't know how many times the AP tried to send the frame previously. It wasn't able to understand/receive those previous attempts.
If it is from client to the server, you may be able to write/use a specialized driver that could give you these statistics, but that may depend on the hardware as well. Of course, the results will likely change whenever any environmental conditions change.
Say for 200 packets from application how many re-transmission in IEEE 802.11 layer?
There is no way to say without actually measuring this in some way, but some enterprise wireless systems can provide retranmission/retry statistics (at least from AP to client).
When an 802.11 frame is transmitted and no ACK is received, it is retransmitted a certain number of times. Once a threshold of retransmissions is reached, the data rate is adjusted downward to try again.
Now different vendors apply the standards in slightly different ways to try to optimize wireless traffic so their product out performs competitors. These optimizations are often only known to those inside the company. Some of the differences could be (don't take this as a full list):
- How many retransmissions before a lower data rate is tried?
- How is the next data rate selected when lowering the data rate?
- The next lowest MCS value (802.11n/802.11ac)?
- The next lowest SS value (802.11ac)?
- The next lowest data rate irregardless of MCS/SS values?
- Does it skip data rates/MCS/SS values on the way down?
- Some combination of the above?
- How many total retransmissions to allow before entirely dropping the frame?
- Which data rate is the next frame started at?
- Start from the highest client supported data rate (i.e. aggressively try for the best data rate all the time)?
- Start from a value slightly above the last successful tranmission (i.e. conservatively increase the data rate for least retransmissions)?
- Maintain statistics for each client and start somewhere on the upper portion of the bell curve (i.e. where 75-90% of the successfully delivered frames are below that data rate)?
- Some other algorithm or process?
- Do any of these shift based on other external factors (number of clients, noise levels, etc)?
Which brings us to the other environmental factors that would be specific to where you were trying to determine the answer to how many retransmissions. How much noise in the RF environment and does it fluctuate? How many other devices trying to communicate on the same channel? And so on.
Asking anyone to tell you how many retransmissions you will have is simply impossible. It needs to be measured.
Or Is there any way to stop the IEEE802.11 re-transmission feature?
Never seen one and I doubt you will. As I have elaborated above, the retransmission process is part of how frames get delivered at the best possible data rates. Some vendors allow a bit of "tweaking" to the specifics of how many retransmissions take place at different points in the process, but to eliminate them entirely would generally be a very bad idea.
The best you may be able to do is to reduce the number of retransmissions to a minimum threshold. For instance, find a vendor that does allow some "tweaking" to settings such as the number of retransmissions. Then configure a client to only support a small subset of data rates or a single fixed data rate (this will have to be the only base/basic/required supported by the WLAN as well). You would have to pick a slower data rate that would provide for reliable delivery of frames in all conditions.
