@David-TP 

Hi David,

Thanks for your reply.  I was using OOKLA to do a download test as a way of testing how the Decos switched from one to the other as you walked around the house.  The OOKLA app failed when I had walked from the deco where I initiated the download to one of the other decos.  When I looked on my phone to see what the SSID was it was no longer the DECO SSID but my main router, so yes, it had disconnected from my DECO and connected to a completely different network.

On the second point about the backhaul, here are the screen shots relevant to my garage - as you can see there is no backhaul icon (as far as I can see).  The 3 decos are on the same panel but different breakers (fuses as I think they used to be known!).

I used to have TPLINK AV600 powerlines on the same electrical sockets and they worked fine

This is the map in list mode:

This is for the garage:

I'm a bit uneasy about using BETA firmware since as someone pointed out in the referenced page, their decos never worked again after putting it in!

Thanks Allen

  @AllenK 

Just to add to my previous post, I've just plugged both the main deco and one satellite into the same double socket and the APP still doesn't have the backhaul symbol between them, so if that symbol is meant to be present then I think that there is definitely something wrong with what I have.  

Allen

  @AllenK 

A bit more information.  I've deleted the decos, done a factory reset on each of them and switched the main deco with one of the satellites.  It still doesn't work. (somebody suggested this as a possible solution).  Is there a tutorial on how to update the firmware because I think that that is going to be my next step.

Thanks Allen

  @AllenK 

So I've now tried to do a firmware upgrade using the instructions supplied with the upgrade.  This did not go well.  I tried this:

Step 2 Launch a web browser, enter http://tplinkdeco.net or the LAN IP address shown on the Deco app in the address bar to access the web management page of the Deco

the tplinkdeco.net did not exist and the LAN address for the main (wired) deco firstly said it was insecure, but when I ignored that it eventually came back with:

This page isn’t working

192.168.68.119 didn’t send any data.

ERR_EMPTY_RESPONSE

Unless you have any other suggestions I think that I will send these back.  The decision I have to make then is do I buy another set and just hope that these were duff in some way, or do I give up???

thanks Allen

  @AllenK 

Do you still have TP-Link AV600 powerline adapters?

  @Alexandre. 

I do.

  @AllenK 

In that case, it would make sense to return P9 set and get different Deco model, or even try different WiFi mesh brand.

If going with Deco, I would suggest M5 or M9 Plus. Deco M4R is also a good option, if you don't need features from latest M5 firmware.

The Deco unit you will be placing in garage should work over TP-LINK powerline adapters.

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As for your phone switching to router WiFi, the fix is to turn off WiFi on router. It appears your phone gets confused where to switch when signal it gets from Deco node becomes weak, connects to router instead of different Devo node. This is your phone decision TP-LINK Deco does not have control over. 

  @Alexandre. 

Hi

Thanks for your post.  I'm returning the P9s but I'm also ordering another set (of P9s).  As I mentioned earlier I have plugged the main deco and one of the satellites into the same double electrical socket and they do not show the powerline being used, so I am hoping that I have a duff set and that a replacement set might work (I can't really believe that TPLINK would ship a product that simply does not have one of the main advertised features).  If this doesn't work then I will probably go back to my old system.

As for the switching to my main router rather than one of the other Decos, I've done what you suggested and it now sticks to the decos, but I can't see what makes the switch from one deco to another 'seamless' but the switch from a deco to a router (or from one access point to another access point) 'not seamless'. Surely my phone doesn't know the difference between a mesh system and an ordinary system, it just switches from one point to another stronger point, so how can it be different?  (My career was programming mainframe computers but I avoided anything to do with comms because it was a nightmare!)

I've just found the firmware version for the decos.  It is 1.1.3 Build 20201228 Rel 55057.   Seems a bit old to me.

Allen

AllenK wrote

As for the switching to my main router rather than one of the other Decos, I've done what you suggested and it now sticks to the decos, but I can't see what makes the switch from one deco to another 'seamless' but the switch from a deco to a router (or from one access point to another access point) 'not seamless'. Surely my phone doesn't know the difference between a mesh system and an ordinary system, it just switches from one point to another stronger point, so how can it be different?  (My career was programming mainframe computers but I avoided anything to do with comms because it was a nightmare!)

  @AllenK 

This is far from original topic of conversation, but telecoms world was substantial part of my career, so I'll explain the basic principles. WiFi mesh operates on the same ideas as cellular phone service, which means WiFi mesh concepts are very familiar to software developers writing communication stack for smartphones and were easily incorporated.

Suppose you and me live in the same area, but with quite distance from each other. You have cell phone. It is connected to what is called "base station" with all cell traffic (voice/data) for that phone passing through it. You started conversation with someone over cell phone, then went outside with the phone, got to your car, drove all the way to my house while still talking over the phone. With cell phones, that doesn't surprise anyone.

There was no conversation interruption, even with cell phone jumping between base stations on your way to my house. It is because there is central authority (or dispatch), which is cellular carrier data centre, and it knows everything about your cell phone. When signal to the base station becomes weak, your cell phone will scan area, find new base station with stronger signal and ask new base station permission to connect to it. Base station will report this request to central authority (data center). If connection is permitted, data center will start sending voice/data for your cell phone to the new base station. It will also stop sending voice/data for your cell phone to the previous base station.

The switch will seem seamless, but in fact there might be a tiny interruption. For voice calls it'll be absolutely unnoticed, and for data traffic it'll be mitigated by resending few data packets. You might see speed of connection very briefly slightly decrease, but it'll not be interrupted - as data for your cell phone continues to flow to the new base station from the point it stopped to flow to the previous base station.

Deco WiFi mesh has Main Deco that knows everything about mobile device connected to Deco, and which other Deco that mobile device wants to reconnect. Main Deco can direct traffic destined to this mobile device to that other Deco, so that switch will be seamless and data traffic to new Deco mobile device is connected to will resume at the point at which it were cut off on Deco mobile device was connected previously.

As for ordinary routers, pre-mesh, they operate more or less like landline. Taking same example, in the world before cell phones if you call someone on laldline and have to leave, you are going to say something like that: "I have to leave for Alexandre's house, I'll call you back from there." You hang the phone, drive to my place, ask permission to make a call from my landline and if I don't mind, you make that call. There will be quite long interruption between your calls, while you were driving.

With both router and WiFi mesh at your house you created the situation I can explain based on same example. It is as if you have both cell phone and landline at your house. You started an important conversation over the cell phone, but suddenly quality of call deteriorates, for some reason. You tell person you are talking to "hold on, I'll call you back from landline."  There will be interruption while you are switching from cell phone to landline call, but you decided to do that. It is your decision.

This is what your device did. It has found router WiFi with stronger signal and decided it doesn't care there will be an interruption while it connects to the router. It were device decision.

On that same example: what if you don't have landline at your house? You'll be forced to continue conversation over the cell phone, even if quality of that call fluctuates. You will have no choice. By turning router WiFi off you left no choice for your smartphone: it has to stay on WiFi mesh no matter what.

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PS. This is very simplistic description of the cell phone and WiFi mesh communication principles. Many important things omitted or oversimplified.