@Jan81 

1) as I understand it, the big + of mesh is seamless roaming.

- does this still function while using the Deco's as AP?

- does this still function with wired backhaul?

Yes and yes. As long as WiFi signal from nodes overlaps.

I have mesh that consists of wired Satellite M5 (basement), wired Main M9 (first floor) and wireless backhaul Satellite M9 (second floor). Roaming works very well.

Roaming tests I performed:

1. Started to stream 4K video in YouTube on tablet, while standing in front of M5 and previously verified that tablet is connected to M5. Started to walk from basement to first floor to second floor to the far corner of second floor. Steaming did not stop and was not interrupted during the walk. Verified that at the end of the walk tablet is connected to Satellite M9 from second floor.

2. Standing in front of Satellite Deco M9 on second floor, started SpeedTest on smartphone connected to it by 5GHz WiFi. Speedtest reached ISP provided download speed of 300Mbps. At that moment, powered off second floor Satellite Deco M9. Speedtest started to slow down till it reached about 60Mbps, then ramped up back to 300Mbps. Test was not interrupted and didn't drop to zero. When speedtest completed, verified that smartphone is now connected to Main Deco on first floor.

That means, if you are streaming, or are on VoIP call, on Skype/Zoom, etc - you can move freely all over the house, with properly placed Deco nodes.

2) wired backhaul 

- could/should all nodes connect to 1 switch, the switch being linked to the ISP modem/router?

- or does node 2 link to the free port on the main node and node 3 to the free port on node 2, leaving a port free on node 3 to connect my desktop PC?

With Deco mesh running in AP mode, it does not matter. Whatever is convenient for you.

4) M5  vs M9 

- for use with wired backhaul, would M5 be the smarter choice or is the M9's so much faster its the investment that makes the most sense?

You are not using M9 major benefit: its backhaul on a separate channel, so perhaps M5 can work for you, too. Yet, someone said WiFi M5 signal is weaker that M9. Which means, the answer is: it depends. Depends on distance signal must travel, walls, etc. 

In my case, I placed wired Satellite M5 in the finished basement where my small home office is, and M5 is in location visible from any corner of the office. With that kind of deployment, I really didn't need M9 there. For the rest of the house: 1st and 2nd floor, I think I'll stay with M9.

5) network used 

- does the Deco's wireless network have access to my home LAN (enabling my wired desktop PC to connect to Deco wifi clients) 

Yes, with Deco mesh running in AP mode they should have access, as they will be on the same network.

@Alexandre. 

Thanks for the reply! It's starting to make sense to me now :). 1 thing that bugs me: - I have connected Node 3 with the available LAN cable (going directly to my router, as does Node 1). So only Node 2 is now wirelessly connected. But Node 3 is still using wireless backhaul. What gives?

@Jan81 

That usually means one of two things: problems with wiring/hardware, or Deco mesh running in Router mode.

For starters, please check that your Deco mesh is configured to run in Access Point mode.

@Alexandre. 

I can confirm its in AP mode.

I can transfer a 450Mb file in little over 7 seconds through the cable (desktop to wired laptop on same router). Fair enough for HDD to SSD I guess?

Now something weird: I have found the following image on TP-Link FAQ

Option 1: obviously 2 routers behind eachother will mess things up, so that's why my deco's are in AP mode.

Option 2: I tried this, with 1 extra Deco connected through wifi, but ethernet backhaul did not work

So I figured I'd try option 3, re-plugging the cable that went to Node 3 to Node 1 instead of my modem/router, making Node 1 and 3 wired and Node 2 wireless. Accoording to this TP-Link FAQ that should be possible.

Result: red lights on all deco nodes, no wifi on either Node

@Jan81 

Please repeat setup of the last picture, but ensure it is done in the following way:

Power off Node 2 and leave it as is

Power off Node 3 and bring it to where Main Deco is

Have Main Deco connected to ISP router by short Ethernet cable, preferably one that came with set of Decos, and see that Main Deco LED is green

Use another short Ethernet cable of good quality to connect Node 3 to second port of Main Deco

Power on Node 3

So, you will daisy chain them: 

This should absolutely work, regardless if your Deco mesh is in Access Point or Router mode. Both Decos should stay with green LED light and Node 3 should report Ethernet backhaul.

Let me know if this was successful.

@Alexandre. 

Progress...

- Powered off Node 2 and 3.

- Connected Node 3 by ethernet to Node 1 and powered on: working Ethernet backhaul.

- Powered on Node 2 again, and Node 2 is now connected with wifi backhaul, while Node 3 still has ethernet backhaul.

Also, I got confirmation from the Dutch customer service that it is NOT possible to hook de Deco's up to the modem/router ports. Not even in AP modus. They've been trying to get that FAQ I mentioned earlier offline, but to no avail.

Now if only the connection from my telephone would be handed off from Node 2 to Node 3... being right next to me... -sigh- (yes, fast roaming is on)

EDIT: thinking about what went wrong... there is a very slim change I tried to hotplug the ethernet cable. Not sure though.

Jan81 wrote

Also, I got confirmation from the Dutch customer service that it is NOT possible to hook de Deco's up to the modem/router ports. Not even in AP modus. They've been trying to get that FAQ I mentioned earlier offline, but to no avail.

 

@Jan81 

There must be some sort of miscommunication, because this is how I run my wired Decos in a mesh configured in Access Point mode:

Also, glad to hear you managed to make Ethernet backhaul working.

@Alexandre. 

Wut?! We keep learning. I'm glad it's working now.

Apprantly TP-Link NL doesn't know what TP-Link international is up to and vice versa.

But just a wild guess: maybe most of the ISP provided modem/routers here in The Netherlands don't handle AP Deco's as well as their int. counterparts.