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]

Thanks Ovais,

the visuals, and your explanation really help.  The more im learning, the more there is to learn, and I also understand why this is/can be a single career, so much to learn and know.

About the lecture hall, it seats about 60 people and really isnt that big, maybe 30ft x 30 ft and for the most part people dont roam.  it sits between a corridor and another area, in the corridor there is an AP, and the other area has an AP.  So, if Auto on channels wasnt doing a good job, then it is possible that one or both of those other AP’s was using the same channel as the LH AP.

I guess I have a couple of options:  1) wait until i get a complaint and check the interface and see if any of those two AP’s are on the same channel, if so, then its possible thats the issue.  2) change all three of those AP’s to different channels, and then monitor that for complaints.

Im going to go through all the AP’s where they are fairly close, and make sure there isnt one on the same channel; at least this way, im taking a potential issue out of the equation.

Thanks SO much for your time in explaining all of this to me, its been extremely helpful.  Have a happy day.

Ill post back here what the results are; may be some time though (a couple weeks tops).

Best,

Jason.

[Ovais_Qayyum]

Hi Jason,

Here is the answers to your first two questions:

If the channel is set to Auto on the AP’s, wouldnt the AP use a different channel from the one thats closest? Because in checking, wifi1’s channels are set to Auto on pretty much all our AP’s.

Auto channel assignment is enough usually but its not perfect and some network environments may require you to either have static channel plan OR have Auto channel assignment select the channels and then you tweak the channels as needed. It is more important in networks where only limited no. of channels are available for use, which means channels will be repeated many times over on different APs which may create CCI. I am not sure what your channel profile looks like, if you are using all non-DFS channel or just UNII-1 channels are being used. The recommendation would be to skip DFS channels and use all the remaining channels. I assume this is most likely already the case.    

This issue only applies to AP’s close to each other AND using the same channel, right?  For instance, in one building there is an AP on channel 161, and then in a different building - a long distance away - there is another AP thats on channel 161.  Because of the distance, we wont have the issue you explained, correct?

That’s correct, the issue will surface only when you have APs in the hearing range of each other while using the same channel. The following diagram should help visualize that; here channel 6 is the cause of CCI since two APs can hear each other on channel 6 which will cause the APs and their associated clients to compete for channel access.

We seem to have the rx/tx retries in one place more than others, the SU Lecture Hall. My first screenshot was of that one.  I just checked it, and its not on the same channels as the 3 closest AP’s.  At least its not now, but of course this is many hours after the issue.

In this particular location, your problem may not be the CCI due to other APs but If you have a large no. of concurrent clients on this AP which are all: 

• Actively doing Tx/Rx
• Using any application that utilizes broadcast/multicast etc.
• Legacy 802.11b/g clients which are slower and drag the faster clients with them
• Clients that are located far from the AP will also increase retries, because these clients won’t get Tx opportunity as often as the clients located closer to the AP, hence they keep re-trying.   
• Clients that are sticky and not roaming away from the lecture hall AP when they really should move on to the next better AP. This is a very common problem with hand-held client devices. These clients will kill the performance of the AP.
• If its a large lecture hall and the network is designed to cover the hall with single AP, you may have too many clients for a single AP, adding another AP will help load balance the clients across the two APs and free up the channel. But this should only be considered if the above mentioned conditions are not found to be true. 

You should investigate this AP in the light of above and check what’s the cause of high channel utilization and retries. Let me know if this helps.

Regards,

Ovais

[systemscsn]

Oh sorry, mean to make a comment on this part of what you typed

“I would recommend you take a look at the current channel plan to verify if you have APs that are close to each other and have been assigned the same channel. You can use Network 360 (if a floorplan is configured and AP are mapped) to check the AP locations, channel and power information. Another way could be to use “Devices” screen and sort the APs based on Hostnames if you have them by locations and then check the radios stats:”

We seem to have the rx/tx retries in one place more than others, the SU Lecture Hall. My first screenshot was of that one.  I just checked it, and its not on the same channels as the 3 closest AP’s.  At least its not now, but of course this is many hours after the issue.

Just wanted you to know.

thanks,

J.

[systemscsn]

Thanks for the links, ill be sure to check them out (today is the first day of school, and the students are back today, so its a bit crazy).

Quick couple of questions on AP’s close to each other AND using same channel.

If the channel is set to Auto on the AP’s, wouldnt the AP use a different channel from the one thats closest? Because in checking, wifi1’s channels are set to Auto on pretty much all our AP’s.

This issue only applies to AP’s close to each other AND using the same channel, right?  For instance, in one building there is an AP on channel 161, and then in a different building - a long distance away - there is another AP thats on channel 161.  Because of the distance, we wont have the issue you explained, correct?

I really appreciate your time on this.  The issue we had with our deployment, is we literally ran out of time from installing, and getting everything working.  We got it all working the day before school started (bonjour wouldnt work), and so couldnt do any kind of tweaking.

lastly, we have 160 AP’s throughout our campus, does this mean that i have to pick a channel for AP’s that are close enough together where there could be an issue of using the same channel?

thanks again for everything, and for helping me get my head around this, appreciate.

Best,

Jason.

[Ovais_Qayyum]

Here is some good information on this topic from Extreme Networks, this should answer most of your questions:

https://www.extremenetworks.com/extreme-networks-blog/whats-the-biggest-cause-of-co-channel-interfer...

Here is another article on how a 5GHz network should be planned, though it references Extreme Identifi wireless solution but the fact that RF design does not depend on the physical hardware solution makes it valid and valuable:

https://extremeportal.force.com/ExtrArticleDetail?an=000079876

I would recommend you take a look at the current channel plan to verify if you have APs that are close to each other and have been assigned the same channel. You can use Network 360 (if a floorplan is configured and AP are mapped) to check the AP locations, channel and power information. Another way could be to use “Devices” screen and sort the APs based on Hostnames if you have them by locations and then check the radios stats:

Regards,

Ovais