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High OutDiscard Percent on Wireless APs

Posted on 2016-08-31
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Last Modified: 2016-09-04
Hi Guys,

We have a rather interesting issue occurring with our wireless network here. I will provide some background on the setup. We have a 100MB WAN link ---> Cisco 3825 ---> HP 1400 Procurve Switch ---> 4 Unifi AP Pro's. From these AP's we have 2 SSID's being broadcast, HIP and HIP-GUEST both on 2.4 and 5Ghz. The AP's are placed around a large office in a square shape with the channels set to 1, 6, 11, 6 respectively and support on average 100 clients of varying make and model. Each AP has on average 20 - 30 clients connected and each client is capped at a max 2Mpbs. The Utilisation on the router port is only around 20% most of the time.

We are seeing some rather interesting statistics on our monitoring software where the OutDIscard percent of each virtual interface is extreamly high, in excess of 80% most of the time for all AP's and the physical WiFi interfaces report a high number of In and Out packet errors.  Does anyone have any insight as to what might cause this? We have changed out the switch, played around with RSSI and even tried lowering the TX power of the AP's to match the weakest device but all these didn't seem to have much of an effect.

I have attached some files to give a better understanding of what is going on. We are in a very congested area for Wifi, roughly 600 neighbouring SSID's as reported by the Unifi management software.

If anyone can help out with some suggestions to troubleshoot this or any explanation as we are pulling our hair out there! Let me know if anyone wants more information.
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Question by:Anthony Barron
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4 Comments
 
LVL 46

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by:Craig Beck
Craig Beck earned 500 total points
ID: 41780396
In a congested environment this is to be expected.  The medium is shared and co-channel interference can mean that data has to be re-sent multiple times.

Do you see the issue at 5GHz?
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Author Comment

by:Anthony Barron
ID: 41780942
The virtual interfaces (ath1, ath2 etc) we see significantly less OutDiscards on 5Ghz and for the physical Wifi1 interface, the TX and RX errors are about the same as 2.4Ghz.

My main concern is that with the high OutDiscard rates, it is impacting performance on 2.4Ghz. We have several Chromecasts around the office and these are constantly dropping in and out. Is there anything that we can do to lower the OutDiscards or is this the reality we have to live with due to the congestion?
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LVL 46

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Craig Beck earned 500 total points
ID: 41781200
That makes perfect sense.  The 5GHz band is generally significantly less-congested than 2.4GHz so you'll see less outDiscards.

In congested RF environments 2.4GHz is always going to suffer.  That's one of the reasons that 5GHz is recommended for applications such as voice and video.  The 5GHz frequency-band allows for around 19 channels whereas 2.4GHz only really has capacity for 3 (non-overlapping).  As soon as you have more than 3 APs in the same area working at 2.4GHz you're going to suffer with degraded performance.
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Author Comment

by:Anthony Barron
ID: 41784031
Thanks for the clarification Craig. Will look at pushing all the users we can over to 5Ghz from 2.4Ghz.
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