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Hi,

I know that RTC/CTS is used on .11ac for Dynamic Bandwidth Management. Is it also mandatory to use when the APs are set to 20Mhz bonds? 

Thanks

Hicham 

I can tell you CTS-Self is being used for every frame sent at every rate less than 48 Mbps, by some chip manufacturers in both the 2.4 and 5 GHz bands.

Why bother forcing users to get rid of their 802.11b devces if all you are going to do is effectively force protection mode anyway ?

Hi Howard,

Thanks for the reply. I'm wondering if RTS is mandatory in 802.11ac even when the bandwidth is set to 20MHz. 

Thanks

Hicham 

I cannot find any restriction, but then maybe I'm not looking in the right place.    You might be able to find the answer in some chip manufacturers "secret sauce" (document), if you have access to any.     Or maybe in some in-depth Cisco 802.11ac configuration manual. 

According to Matthew Gast's Book on 802.11ac, no new protection mechanisms are required by 802.11ac - which means that none of the existing ones are forbidden.    He says "Re-use of the OFDM PHY's physical layer header ensures that any 5 GHz device will be able to detect VHT transmissions and  identify that the medium is busy."     

It is the case that RTS/CTS pairs are also used with Dynamic Bandwidth Operations using a non-HT duplicate frame.    Gast gives an example of two adjacent, but non-overlapping 20 or 40 MHz wide channels that could still be within the boundaries of an 80 MHz wide channel, and in that case each one would need to use RTS/CTS to ensure the viability of the network.      But I can find no reference to how that would be "managed" by the network.

According to Gast, the only time RTS/CTS is absolutely required is with 802.11n operating in Greenfield mode, and notes that "Greenfield mode was removed from 802.11ac."

Hope that helps some - but his book doesn't seem to answer either of our questions. (it would help if it had an index)

If you find a solid answer on this please share it.

Howard

Thanks Howard! I will keep you posted