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40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

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Head in the Cloud

40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

Hello!

 

I have something like 9 gateways and 9 repeaters on a rural property out in the woods where there is ZERO interference of any kind. We have a 250/250 ATT fiber line on the property (limited to like 120mbit per SSID (of which there is one) per AP). Not too hilly but a bunch of trees that line the areas where people live in. We get great ATT cell signal which fills in the gaps for the most part as people walk across property. The property, where people live and work, is pretty much covered with wifi well. There are a few dropout spots here and there and every now and then you can find a corner that isn't covered. Lots of MR52s. I have relatively zero to low complaints about signal and speed is always rock solid. I have everything set to automatic. And I wonder if it could get *even better* with 40mhz channels. There are at most 150 people on property but thats 1% of the time when we have an event and theyre pretty well spread out and low bandwidth using for things like weddings etc. 

 

 

Is there anything I could test to tell me definitively whether this would be even better? A range test? There is a spot indoors under a metal roof very near a MR74 that doesn't penetrate it too well into the building and I kinda wonder, if I didnt want to spend another indoor MR on it if 40mhz would help it. 

 

Again, not really troubleshooting anything per se. I also trust Meraki HW to downshift on the fly to 40mhz if it detects it would work better. Looking at my client list of about 70 right now (35 residents Macs and iPhones plus a few Sonos devices, printers, etc) the Apple devices are 80% at 80mhz with about 20% of APs at 40mhz. And again, people by and large love the service quality. Only issues come with people who are using ancient (2013) hardware and with that Im pretty sure the antennas and chipset ages are to blame. 

 

Everything is on full auto right now. I dont want to mess anything up!

 

Your thoughts welcome. 

Networking geek since high school where I got half of a CCNA. Played Marathon II and Infinity over localtalk.
Made many a network over the years, now de facto admin of a retreat center with some of this fine Meraki hardware.
Fortune 100 Tech veteran/refugee.
10 REPLIES 10
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Conversationalist

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

In the real world seems 40MHz rock better than 80 MHz. This is true when most of users is using laptops. When more user is using mobile phone or tablet then 80 MHz will rock.

 

Just some experience encounter.

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Head in the Cloud

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

It depends:

- When you go from 20 MHz to 40 you need an 3dB better SNR to achieve the same MCS value.  When you jump to 80 Mhz you need another 3dB.  So when you are using wide channels you are effectively shrinking your usable celsize a bit.
- If you are using omni antennas, you have the chance that by using 80MHz channels you could potentially have co channel interference.
- But if you are using 20 MHz on too few antennas per area and you have allowed alot of bandwidth for every individual user you could easily run into max airtime when users start downloading stuff.

 

Best way is on your current situation to monitor the airtime of each access point when you have an event with alot of users.

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Head in the Cloud

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

I think I understand about 80% of that. I dont have issues when larger parties come but I also havent noticed if it drops the channel width to 40mhz. Presumably, Meraki's auto will handle all this, yes? Its feeling more like I should trust it as it seems to be doing a good job now. 

Networking geek since high school where I got half of a CCNA. Played Marathon II and Infinity over localtalk.
Made many a network over the years, now de facto admin of a retreat center with some of this fine Meraki hardware.
Fortune 100 Tech veteran/refugee.
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Head in the Cloud

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

The auto handling will of course be limited to changing channels and lowering or raising the Tx power.

I would suggest the following:
- if you get capacity issues -> check the airtime utilization on the AP's in the affected area's, due to a bug sometimes you can't see the historical data and need to check the live values.  (Access Point -> RF tab)

- if you have dead spots/coverage spots: do not raise the Tx power if it's already above 14dBm on 5GHz but you need an additional AP.  Normally you should also target for at least some duplicate coverage of a second AP.

- If you have a single user that is destroying your capacity, try to implement some bandwidth limits per user and have some streaming applications to get higher QoS treatment.

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Head in the Cloud

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

@GIdenJoe- I find that the channel width is changing automatically and that there appears to be a seeing in Radio Settings to that effect, no?

Networking geek since high school where I got half of a CCNA. Played Marathon II and Infinity over localtalk.
Made many a network over the years, now de facto admin of a retreat center with some of this fine Meraki hardware.
Fortune 100 Tech veteran/refugee.
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Getting noticed

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

Honestly, 80MHz 5GHz channels is often an underutilized feature because of how scared we are to use it. If you are in a relatively RF-clean environment where you don't see more than, say, 10-20% utilization in your RF Spectrum, 80MHz channels tend to work. This is especially true in home setups or small office sort of venues.

 

80MHz theoretically doubles your throughput compared to 40MHz but even in practice, it is one of the best ways of getting improved throughput on 1-stream and 2-stream devices. Right now in my home office, even on a sort of busy channel (36 with 4 neighboring APs above 80dBm), 80MHz channels on a MR56 with a iPhone 11 Pro gets about 400-450mbit while 40MHz channels gets me 250-300mbit. If you have clients that mostly burst downloading large files, this can make a huge difference in customer satisfaction.

 

It's also worth mentioning that even if you select 80MHz channels, both APs and clients are welcome to select 40MHz or 20MHz rates. There are rate control algorithms on both end that won't even choose 80MHz MCS rates if there's not enough SNR for it to be successful.

 

With that said, where it starts going wrong and these things must be kept in mind:

  • Without DFS channels, you basically have 2 nonoverlapping channels in the US (36-48 and 149-157)
  • Having multiple APs on the same channel is not necessarily evil for low density. It's only a problem if multiple neighboring APs have high traffic, but if you have a lot of APs for the purpose of increasing high-RSSI coverage for maximum throughput, I've had  great success running even two APs in neighboring rooms on the same channel when there's just one critical client that moves between those two rooms.
  • With DFS, you have a few more nonoverlapping DFS channels: 56-64 and 100-112. But you may not even have 136 in your area depending on whether or not your AP supports those channels neighboring weather doppler radar.
  • Furthermore, you greatly increase the chances of a DFS radar event when your channels are wider.
  • If you start having co-channel interference issues where you have high or maybe uneven usage of your 80MHz channels, at that point you have no choice other than to step back down to 40 or 20MHz channels

 

I cannot tell you how often I site survey an office environment and see dozens of APs for an office environment all set to 20MHz channels and less than 10% BSS load on any of the 20MHz channels. There goes your 400-600mbit wifi throughput, you just limited everyone to 100mbit or less.

 

Of course there's situations where that's the right thing to do but the sayings around premature optimization applies to wi-fi too. It's not always the right knee-jerk reaction to read a "Ultra High Density" best practices guide and assume that your own network has got to be ultra-high-density too.

 

Luckily, Meraki gives you lots of great tools to take a look at your RF spectrum and also take a historical look at how many active clients and what kind of utilization/throughput is typical on your network.

 

 

EDIT: One issue I'd like to call out: AutoRF channel changes basically seem disabled when your channel is 80MHz. This is documented on the AutoRF documentation page with a description saying that clients disconnect/reconnect on 80MHz channel changes but this does not appear to be the case when I manually force an 80MHz channel change. Hopefully Meraki can consider revising that behavior for 80MHz.

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Getting noticed

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

1. Based on your use case and rural location, you should use 80 MHz channels. Your repeaters will thank you!

 

2. Meraki's Auto-algorithm is good, but in your case, I recommend trying to manually adjust the 5 GHz channels, ONLY on your gateways. Remember there are only a handful of non-overlapping channels (36+, 52+, 100+, 166+, 132+, 149+, and 165) available in the 5 GHz band when using 80MHz wide channels. So start with those channels, and then re-use channels only on access points far away from each other.

 
 

Screen Shot 2020-04-02 at 2.50.26 AM.png

Colin Lowenberg
wireless engineer and startup founder, formerly known as "the API guy", now I run a Furapi, the therapy dog service, and Lowenberg Labs, an IT consulting company.
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Head in the Cloud

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

@colinster @Thanks! The gateways are generally far enough from each other that I’m not really worried about them interfering On 5ghz. They all seem to have intelligently figured out their channels. I think my main question was about getting a little more range in exchange for unutilized bandwidth but I think things are probably good.

Networking geek since high school where I got half of a CCNA. Played Marathon II and Infinity over localtalk.
Made many a network over the years, now de facto admin of a retreat center with some of this fine Meraki hardware.
Fortune 100 Tech veteran/refugee.
Highlighted
Getting noticed

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

@RumorConsumerI'd be happy to take a look with you on a zoom call. I spent 10 years designing wireless mesh networks and worked on mesh at Meraki. Schedule me here: http://calendly.com/colinster

Colin Lowenberg
wireless engineer and startup founder, formerly known as "the API guy", now I run a Furapi, the therapy dog service, and Lowenberg Labs, an IT consulting company.
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Head in the Cloud

Re: 40mhz v 80mhz channel width on rural 5ghz - It aint broke but boy am I tempted to fix it

@colinster We might just do that. I recently posted this:

 

https://community.meraki.com/t5/Wireless-LAN/WLAN-speeds-suddenly-became-erratic/m-p/91249#M13427

 

 

I think reflecting on this thread might have given me the answer to what was going on.

 

At one point in the last month or so I created a new RF profile which removes UNII-1 ranges. I applied this profile to two of the affected three stations. The plan had been to integrate a point to point Ubiquity shot which uses UNII -1 and I didnt want our Meraki stuff stepping on its toes. That ended up not happening (we found another solution) but in the meantime developed the problem in the above thread. What I didnt realize and now gather was that DFS prevents the use of some of those middle channels, so effectively there was some co-channel interference at 80mhz with UNII1 off limits. We changed to 40mhz channels and reenabled UNII1 on all APs and the speed issue seems to have disappeared. I think we could probably reenable 80mhz channels but I dont think it will make a huge difference for us in terms of speed as I cap WAN bandwidth at 150mbit and we aren't sending a lot of big files that would necessitate 80mhz wide channels. Does that all make sense to you?

Networking geek since high school where I got half of a CCNA. Played Marathon II and Infinity over localtalk.
Made many a network over the years, now de facto admin of a retreat center with some of this fine Meraki hardware.
Fortune 100 Tech veteran/refugee.
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