Why so many retires, but only on wifi interface

[systemscsn]

Recently we got rid of the 2.4ghz band on wifi interface wifi0 and replaced it with 5ghz, leaving interface wifi1 alone (802.11ax_5g) radio profile radio_ng_11ax-5g and channels set to Auto.

Heres what i noticed, and its probable that this has been going on all the time, but with more devices connecting to wifi1, we now see the issue.

only on wifi1 am i seeing a ton of RX TX retries.

What is the reason for this?  thats an insane amount of retires, and notice how the other is totally fine.

any ideas?

thanks,

J

[systemscsn]

Guess i didnt know about that whole using the same channel thing - even if the device isnt on that AP.

So, i have 56 clients on that AP, and somewhere around are another 72 clients on a different AP, but if both AP’s are using the same channel, then both AP’s “hear” the other clients?  is that what you are saying?

Because we have two other AP’s in the general area, and while i don't know for sure, id hazard a guess that at least one of them is using the same channel.  I know it wouldn't be #1 as we have AP’s everywhere, probably too many.

im thinking if the above is true, then what?  reducing the power isnt going to help! and id bet I cant configure each of the 160 AP’s to only use a channel that another AP isnt using (all on their own single channel… probably not  good even if possible).

I appreciate the explanation, it helps, but it makes me even more full of questions. UGH i didnt know that about a channel shared by AP’s close enough to see each other would do that, but it does make sense.

Thanks,

[Ovais_Qayyum · Accepted solution]

Hi J, 

The screenshot has the answer, on 5GHz interface you have got 56 connected clients and the radio can sense another 72 “surrounding clients” which are the clients not directly connected to this AP but may be using the same channel i.e. 161 which may also also be used by another AP. The AP in question may not be the only AP in your environment which is using channel 161. So, with 56 connected clients and 72  other clients that are probing on the same channel 161, the AP will hear a lot of chatter which has increased the channel utilization to 69%. High channel utilization means less transmit opportunity for each client, more collisions, more back-off and more re-transmit attempts. 

There are many reasons for high transmit retry % in a network:

1- Too many Clients and too less of APs/Radios.

2- RF interference caused by the neighboring APs, it could be adjacent channel or co-channel interference. An example would be an environment where APs using the same channels can hear each other loud and clear. 

3- Co-channel interference (CCI) caused by clients, CCI is the no. 1 cause of interference in a WiFi network and it can’t be completely mitigated. Only a properly planned and designed network can help lessen the impact of CCI.          

Regards,

Ovais