What is the value to be set for HW-protection for Mikrotik RTS/CTS? Is that the question?
I don’t have the answer for a specific situation, and it seems to be more complex with 802.11n and 802.11ac.
There is MTU , MSDU and MPDU , where MTU is embedded in MSDU, MSDU’s are aggregated or segmented in MPDU (or A-MSDU), and MPDU aggregated in A-MPDU, the transmit frame size.
In older (and non-mikrotik) equipment , it was simple: https://networkengineering.stackexchange.com/questions/32970/what-is-the-802-11-mtu
MTU for wifi is/was 2304 bytes
“On my WiFi AP, I can set the RTS threshold with a value of 0-2346 bytes (I guess it’s MTU + the MAC/PHY header ?)”
Indeed on my Engenius AP’s (b/g/n) also the entry was 2347 for the protection threshold , and 2346 was the max framesize.
This 2347 size was actually the alternative for turning off RTS/CTS , as this size was never reached.
To turn it on, a lower value had to be entered. No guidance except the comment that sending a 60 byte RTS/CTS frame to reserve time for sending a 60 byte data packet was not productive.
Idea is to avoid unproductive RTS/CTS packages, and to directly take the interference risk in the “hidden node” situation for small packets.
A value of 0 would always invoke RTS/CTS.
Survival guide : https://www.oreilly.com/library/view/80211ac-a-survival/9781449357702/ch03.html learns a lot! Important document.
802.11n added aggregation up to 7981 A-MSDU or MPDU frame size.
802.11ac extended the MPDU size list: 3,895 bytes, 7,991 bytes, or 11,454 bytes
The total A-MPDU size evolved from 4,095 bytes(a/g) over 65,535 bytes(n) to 4,692,480 bytes(ac) , if the devices allowed for it.
Interesting to see is that all RouterOS devices I tested only mark 3839 MPDU sizes in their beacons for 802.11n and for 802.11ac . http://forum.mikrotik.com/t/ac2-vs-ac3-wifi-not-over-200mb/148289/1
Where other devices take the standards maximum byte size values 7935(n) and 11454(ac).
Leading to potential large overhead in MT when high interface rates where used, and lower throughput than the other implementations.
And then in the surval guide … there is … the reuse of the RTS/CTS mechanism for the “Dynamic bandwidth Operation” checks for wider channels with 802.11ac.
Is this used by MT ?? Does this overrule the RTS/CTS protection mechanisms ??? No idea !!! Don’t know how to check that. (because of multiple channels!).