MESH Linked EAP225_Outdoor Kinda Slow

Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-09 11:23:41

@Doc2485, I also agree that wireless links between APs should always be avoided in business installations. But there are situations where you just can't wire up APs, e.g. if you need to deploy a WLAN in listed buildings (historic buildings), which require permission from authorities to even drill a hole in a wall or a ceiling for a cable duct. Much paperwork and at the end it can be that authorities don't permit it at all.

 

@JSchnee21, the goodput you can reach over a wired EAP is already 50% (a/b modes) or 70% (g/n/ac modes) of the WiFi rate. The other 50% loss of throughput comes from the wireless mesh link, so yes, you're right that a first-hop mesh node will only achieve a ¼ of the average of both WiFi rates between both meshed EAPs and between the last EAP and the client.

 

What's more, the mesh network is subject to the Hidden Node Problem if clients share the 5 GHz mesh backhaul. Thus, turning off the 2.4 GHz band of a mesh node can increase interferences in the 5 GHz band.

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Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-09 11:49:58

Hi R1D2,

 

Could you clarify this:

 

"What's more, the mesh network is subject to the Hidden Node Problem if clients share the 5 GHz mesh backhaul. Thus, turning off the 2.4 GHz band of a mesh node can increase interferences in the 5 GHz band."

 

Ideally, I would think that it would be better to have clients on the 2.4G radio rather than the 5G so that the 5G was "free" for backhaul.  I think that is what you are saying.  That is, if you host an SSID on both radios (with band steering) but turn off the 2.4G, then clients will be shifted to the 5G and compete for airtime with the backhaul.

 

This was my recommendation to ByteGuy recently (put all STA's on 2.4G and leave 5G free for back haul) given his extensive MESH setup.  Especially since each STA is throttled / BW limited to 10Mbit/sec DL & UL anyway.

 

But, I'm not sure if my suggestion was ever fully implemented.

 

-Jonathan

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#13
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Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-09 12:41:05 - last edited 2020-06-09 12:51:36

 

JSchnee21 wrote

Could you clarify this:

 

"What's more, the mesh network is subject to the Hidden Node Problem if clients share the 5 GHz mesh backhaul. Thus, turning off the 2.4 GHz band of a mesh node can increase interferences in the 5 GHz band."

 

All devices always listen to wireless signals in order to detect whether some device has successfully acquired the channel for sending data. That's part of the standard Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanism. As long as they detect a signal, they will pause.

 

Now, if the root node wants to send data to the mesh node, it waits for silence, acquires the channel and sends data to the mesh node, which in turn will send it to the client. The root node still can detect that the mesh node is currently using the channel to send data to the client.

 

But if the client replies and the root node cannot receive the client's signal, it could falsely detect silence, send more data to the mesh node and collisions / interferences will occur at the mesh node which now receives data from two devices, the client and the root node.

 

This is called the Hidden Node Problem, b/c the client is hidden to the root node. The HNP is what makes repeaters, which always use the same channel as the AP whose signal is to be repeated, so unreliable.

 

Ideally, I would think that it would be better to have clients on the 2.4G radio rather than the 5G so that the 5G was "free" for backhaul.  I think that is what you are saying.  That is, if you host an SSID on both radios (with band steering) but turn off the 2.4G, then clients will be shifted to the 5G and compete for airtime with the backhaul.

 

That's the solution to avoid the HNP. If the 2.4 GHz SSID or radio is turned off, clients will connect to the 5 GHz band regardless of the band steering setting in Omada controller.

 

Note that interferences (resp. collisions) don't prevent communication at all, but goodput will be decreased significantly if interferences reach a certain level. As long as there is enough AirTime, collisions don't harm. Collisions are still detected – even a sender listens to what it sends and thus can verify the data transmission –, but better than detecting it is to avoid collisions at first.

 

This was my recommendation to ByteGuy recently (put all STA's on 2.4G and leave 5G free for back haul) given his extensive MESH setup.  Especially since each STA is throttled / BW limited to 10Mbit/sec DL & UL anyway.

 

Yes, you're correct (as always :-) ).

 

If we deploy a mesh, say, in a hotel, it's often b/c we need to extend WLAN to a room which is badly covered by the main EAP. In this case (only few client devices expected) we enable both frequency bands for clients. But if the meshed EAP should serve a whole floor and total goodput decreases during heavy use, it can help to enable just the 2.4 GHz band for clients and use the 5 GHz channel only for the backhaul.

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Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-10 02:37:15

R1D2,

 

Thank you for the sanity check.  Makes sense.

 

I cannot wait for an EAP with the new Qualcomm 1210 Wifi-6E platform -- 4x4x4 (2.4G, 5G, and 6G).  Or even the 810 with 2x2x4.  4 stream, 160MHz, on 6GHz will make for some sweet wireless backhaul.

 

doubleu, doubleu, doubleu dot snbforums.com/threads/qualcomm-rolls-out-wi-fi-6e-lineup.64418/

 

Do you have 6E in the UK/EU?

 

-Jonathan

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Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-10 06:25:48

 

JSchnee21 wrote

Do you have 6E in the UK/EU?

 

Authorities here still work on EU-wide rules. They are not the fastet if it comes to real work.

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Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-10 11:50:50

Ha Ha Ha!

 

My employer has a large site in Belgium and we work with them routinely.  The running joke in our office is that everytime we meet with them to "just get something done" they always want to setup even more meetings, have more discussion, and make more PowerPoints!

 

The American / Nike concept of "Just Do It" is totally lost on them.  Often our needs, requirements, priorities change so fast that if you plan and pontificate for too long you'll miss the opportunity to respond in time.

 

-Jonathan

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Re:MESH Linked EAP225_Outdoor Kinda Slow
2020-06-10 14:59:40

 

JSchnee21 wrote

The running joke in our office is that everytime we meet with them to "just get something done" they always want to setup even more meetings, have more discussion, and make more PowerPoints!

 

To just get something done in the EU, you need to fill in up to 15kg declarations of compliance with EU rules on paper and have to wait 3-5 years until the thing you want to do would principially get approved if there were not the new rules from last year, which changed certain regulations again. :-)

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