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Forum Discussion
CTS/RTS and "hidden node problem"
Hey all I have my CTS/RTS value set to 2100. I recently changed the setup on the RBK752 to use a wired backhaul (15m CAT6a run). I've reduced 2.4Ghz power to 25% and 5Ghz power to 50%. I have ...
Jimbo84 wrote:
My question - does a 2 node setup, with wired backhaul, suffer from the "hidden node problem"? I was looking on Wikipedia and the example given shows 3 stations communicating with each other. As the RBK752 is a 2 node kit, am I safe to assume this is not an issue here?
Yes, any WiFi access point can be affected by the hidden node problem. That Wikipedia article was illustrating one Access Point (AP) and two user devices. When there is one router and one AP, then there are two access points that can be affected by the hidden node problem. When there is one router and two APs, then there are three access points that can be affected by the hidden node problem. With the Orbi mesh system, all access points and all user devices broadcast on the same frequency, so collisions can be more common.
Changing from WiFi backhaul to wired backhaul eliminates any possibility for hidden node issues on the backhaul frequency. Just like changing the transmit power affects only the user facing radios, changing the CTS/RTS value on the user facing interfaces most likely has no impact on the WiFi 'backhaul' link between units. The WiFi backhaul transmit power and RTS/CTS are not changeable by the user.
Reducing the access point transmit power will tend to reduce the chances of a hidden node. The reasoning is this:
- When the AP is transmitting at full power, user devices can be farther away and still get a strong signal.
If one user device is very far away from another user device, they may not recognize when each other is trasmitting. - When the AP is transmitting at reduced power, those user devices will have to be closer to the AP, and thus closer to each other.
- However, reducing AP transmit power does not cause user devices to reduce power. So when devices are closer together, they are more likely to hear each other transmit.
There are many articles on the internet discussing how to optimize RTS/CTS for a specific environment. My take from reading them is, "It depends." i.e. there is no value that works best for everyone and all the time.
Thanks CrimpOn that is very informative.
And an interesting point that you make "...So when devices are closer together, they are more likely to hear each other transmit." I have reduced transmit power on my laptop(s) and PC so that their WiFi 6 adapters are transmitting on the "1. Lowest" setting, via Device Manager, to help reduce devices cluttering up the airwaves. And they still seem to pick up full signal which is good. :smileyhappy:
I'll try and do some more research but it is hard with a lot of conflicting information on where to start. Go too low and you are adding unecessary latency to the network having to wait to send data, but go too high / disable CTS/RTS altogether and you can get collisions and re-transmission on larger data packets which slows down throughput (if I understand correctly).
If I were wanting to try and keep all devices "happy" (especially mobile calls over WiFi) would your advice be to have a lower CTS/RTS value to help in this situation. As voice data is real-time and can't be re-transmitted I guess having that "all clear to send" is a good thing?
Thanks.
Jimbo84 wrote:If I were wanting to try and keep all devices "happy" (especially mobile calls over WiFi) would your advice be to have a lower CTS/RTS value to help in this situation. As voice data is real-time and can't be re-transmitted I guess having that "all clear to send" is a good thing?
Are you experiencing a problem with devices on your network and that you're trying to resolve with these adjustments? If not, then I recommend not trying to fiddle with your settings or else you're not able to detect if you're making things worse vs. better.
For most Orbi customers the default settings are fine and if they are not experiencing issues with their wireless network, they don't need to go into the Advanced Settings and make changes to things like CTS/RTS Threshold.
Hi Mikey94025 - yes originally I was trying to fix the issue with WiFi calling on the Orbi kit.
Do you happen to recall what the default value is for CTS/RTS? I'm happy to put this back to default to begin with and see how things pan out.
Thanks.
Jimbo84 wrote:
Hi Mikey94025 - yes originally I was trying to fix the issue with WiFi calling on the Orbi kit.
Do you happen to recall what the default value is for CTS/RTS? I'm happy to put this back to default to begin with and see how things pan out.
There appears to be no single default value for CTS/RTS. On the original Orbi, the default value was 2347 (the maximum possible). When the AX product came out, the default was set to 64. I have a memory that someone spoke to a Netgear engineer who said something along the line of... "our lab environment had so much WiFi going on that we had to set the value to 64 to get things to work." This indicates (to me) that there is no value that is best for every situation. (If there actually is a best value, then Netgear would set the default to that and not let customers change it.)
