CSMA/CA threshold for cisco products.

IgorFi · ‎08-23-2018

Hi folks.

Does anyone know what is CSMA/CA thresholds for Cisco APs. By that I mean how low should be a received dBm for one station to ignore the signal from another station on the same channel to avoid same channel competition? I'm interested is Cisco Air 3800 particularly.

Thank you.

RichardAtkin · ‎08-23-2018

This isn't quite the context/answer to the question, but I suspect it's as close as you'll get... The Enterprise Mobility Design Guide says to aim for at least 19dB separation between different radios on the same channel..

https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-5/Enterprise-Mobility-8-5-Design-Guide/Enterprise_Mobility_8-5_Deployment_Guide/Chapter-9.html#pgfId-1149071

IgorFi · ‎08-23-2018

Hi Richard. The read was not really related to the topic, but it was a good read, nonetheless. I haven't found the answer regarding the CSMA/CA threshold (that's not even an official notion), but had a look at the Cisco 3800 Data sheet and found that at the Rx sensitivity ending at -102dBm. At -102dBm the associated client can send and receive at 1Mbps only. So I guess that at around -104/105dBm, two station won't see each other (but that's a long way!). But I'm pretty sure that CSMA/CA would start ignoring another AP at higher values than -102dBm.

RichardAtkin · ‎08-23-2018

Good luck actually achieving -102, that’s way below the noise floor in most of my deployments! :-/

It’s the Clear Channel Assessment threshold you’re after.

Depending on why you’re looking for this, you might also want to look at Rx-SOP too, which allows the AP to effectively manipulate the CCA threshold.

IgorFi · ‎08-23-2018

"Clear Channel Assessment threshold", - Richard, you just finished my searches. That's exactly what I was after. I'm sure the "-103dbm" was not necessarily. Thank you very much. Interesting, a CWNA (Sybex) book doesn't have anything about it. Can you advice some books that go deeper than that? Cheers.

RichardAtkin · ‎08-23-2018

I learned a lot from “802.11 Wireless Networks” by Matthew Gast. Even the second edition is a little old now (no 11ac, k, v), but it gets in to the nitty gritty of 802.11 and everything is well explained. Give it a read.

IgorFi · ‎08-24-2018

Thanks Richard. I just bought that book and another two - 802.11n and 802.11ac. It gets me busy for the next couple of months.