2.4Ghz high latency solutions

[Diederik_Kuijpe]

I'm currently experiencing some issues with our wireless network I could use some help with figuring out a solution.

The situation is as follows:

I've two EW C25s and 60 AP-3825is. About every classroom, office and common area has an AP. I've the following configured:

The main wlan SSID (2.4+5ghz) is bridged at the AP and connects to internal resources.
The guest network (2.4+5ghz) is a captive portal bridged at the C25 and forwarded to the gateway.
The BYOT network (2.4+5ghz) is RADIUS auth bridged at the C25 and forwarded to the gateway.
The Chromebook network (5ghz) is bridged at the C25 and forwarded to the gateway.

For the most part this work out fine, but recently I noticed a massive increase in latency on the 2.4ghz main network. This is causing problems with new teacher laptops (2.4ghz b/g/n only adapters in them I'm afraid). Pings between 500-2000ms, and terrible upload speeds. It's causing severe disruptions.

What are some things I should check? I have a feeling this is part configuration and part hardware incompatibility. Does anyone recognize this situation?

[Jeff_White1]

If you have an AP in every classroom, office and common area, I would turn off auto tx and statically set the 2.4ghz radio to no more than 5dBm. This is still more power than you need on each AP. I would actually recommend disabling at least half of your 2.4ghz radios but without doing a proper site survey and not knowing building materials, no one would be able to tell you how many to disable, which ones to disable and what power to turn the remaining radios up to.

The issue very well may be a co-channel contention issue. This will eat up airtime on the AP and cause high latency on the network. Because every channel is a contention domain, if an AP can hear another device on the same channel, it can not talk and must wait for the channel to be clear before it can send data. This causes data to queue at the AP and cause latency.

I would start with updating firmware because they have had a lot of buggy versions for what seems like 2 years now. Then I would get a print out of your floor plan and write down the channels the APs are on and adjust if needed. Co-channel contention is unavoidable on the 2.4ghz band, but if you plan appropriately, yo can minimize the effect it has on the network. After that, assuming you have one in every classroom, start turning them down to 5dBm.

[James_A]

09.15 is pretty ancient, I would try 09.21.12.

Apart from the 2.4GHz only devices, what's the 2.4/5GHz split amongst clients? You could consider removing the other SSIDs from some 2.4GHz radios to give some breathing room for your HP ProBooks.

Definitely worth doing a RealCapture to see where the packet delay is occurring too.

[Diederik_Kuijpe]

This is a constant occurrence.

There's a lot of APs with 0 clients, but some will go up to 50 depending on Chromebook usage. Occupancy doesn't appear to matter.

Software version is 09.15.07.0008

I ping the local gateway.

Response times are a little on the high side, but with this particular laptop model (HP ProBook G3 455 / RTL8723BE) it's more severe. I disabled all APs/SSIDS save for the one I need these to work on, strict-n:

I connect my Samsung S5. Ping to the gateway gives min 1ms \ max 89ms \ avg 12.6ms

I connect my iPad Air. Ping to the gateway gives min 1.7ms \ max 40.3ms \ avg 26.7ms

I connect the HP ProBook to the gateway gives min 101ms \ max 2967ms \ avg 410ms

However. when I force the AP in b/g mode the results are much better: min 2ms \ max 3ms \ avg 2ms

If anything it seems a driver problem, but I don't know if it's a setting on the machine or the AP I need to change to make them play nice together.

I'm going to try a few driver versions and see if it helps.

[JP4]

How are the channels and power set on the 2.4 radio's ? Auto channel and max power ? Depending on your floor plan you might have a lot of channel interference in 2.4. Have you used some type of scanner to see how many AP's are on the same channel in a given area ? You can use something as simple as the airport utility on an iPhone as a starting point. 2.4 is also more susceptible to outside interference sources.

[Diederik_Kuijpe]

Where are these RF domains defined? They seems to be on default MyDomain for both radios on all APs.