Seamless roaming from 5 to 2.4 Ghz using one AP - same or different SSID?

[mjc775]

I just finished reading the very informative "Wi-Fi Roaming Secrets Revealed" series, and Apple's "About wireless roaming for enterprise", but neither answered my question specifically - or they're just a bit over my head.

My setup is a Netgear RAX80 router and several iPhone 11 clients. Unfortunately it doesn't appear that the Rax80 offers any 802.11k/r/v roaming standards. I've been experimenting with using the same SSID for both the 5 and 2.4 Ghz band - but NOT using Netgear Smart Connect which let's the router select the best band, not the iPhone. The iPhone selects the faster and less congested 5 Ghz band with medium to strong signal over most of my house. But when I walk out to my backyard - which is on the opposite end of my house from the router - should the iPhone more quickly/easily roam to the 2.4Ghz network using the same SSID or a different SSID? Or should there be no difference?

 

[degrub]

The client device controls the roaming switching, not the AP.

 

[Pericynthion]

I just finished reading the very informative "Wi-Fi Roaming Secrets Revealed" series, and Apple's "About wireless roaming for enterprise", but neither answered my question specifically - or they're just a bit over my head.

My setup is a Netgear RAX80 router and several iPhone 11 clients. Unfortunately it doesn't appear that the Rax80 offers any 802.11k/r/v roaming standards. I've been experimenting with using the same SSID for both the 5 and 2.4 Ghz band - but NOT using Netgear Smart Connect which let's the router select the best band, not the iPhone. The iPhone selects the faster and less congested 5 Ghz band with medium to strong signal over most of my house. But when I walk out to my backyard - which is on the opposite end of my house from the router - should the iPhone more quickly/easily roam to the 2.4Ghz network using the same SSID or a different SSID? Or should there be no difference?

The key thing to note from the Apple document you mention is that the client will only look for a new bssid to associate with, when it’s current connection drops below the -dB threashold. It doesn’t constantly look for a better one to switch to, until the current one becomes an issue.

You can easily prove this if you walk into the garden , turn off and on the WiFi on the phone and it should connect straight to the 2ghz. Some router/APS so have a configuration setting where they will look at the connection table and automatically kick clients off and force them to reassociate (in effect forcing the same behavior). Sounds good in theory but seems to cause a lot of problems with some clients especially ones that move about.

In my experience using the same SSID on 5ghz and 2ghz works just fine and from the client perspective they are all still different connections - even if some do have the same shared key/name etc.


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[Tech Focus]

I know in my case one SSID works even though I have different AP than yours. In theory, I feel separate SSID for two to achieve what you want seems really hard to impossible. Because your iPhone will stick to 5G network as long as it can. Then it reaches to the point finally it no longer can then disconnect/lose connection and now search for different network and find 2.4G with longer range. But this means you have to get kicked out first and be far enough.

In most case, I believe 5G band signal strength become weak but still dominates on actual throughout over 2.4 GHz. But roaming use signal strength so switch happens before 5GHz becomes really weak. So I think even on theory, single SSID would work better for the specific roaming situation you are describing?

 

[thiggins]

Having APs on different SSIDs affects only roaming time because the client needs to re-authenticate. However, on a practical basis, this is moot because consumer device roam times are usually measured in seconds, not milliseconds.

As others have noted and the key point I tried to make in the article is that the CLIENT/STA decides when and where to roam. APs can attempt to influence the process. But in the end, it's up to the client.

That's why some people choose to set different SSIDs per AP, so that users can manually select the closest AP.

 

[mjc775]

My goal was to be able to connect our phones to a single or multiple SSIDs then forget about it - as my wife just wants everything to work everywhere on our property without fiddling with settings.

...consumer device roam times are usually measured in seconds, not milliseconds...

I think this is the key point. If on a Wi-Fi Call, the call will likely drop with my current one router setup.

I did a few experiments yesterday trying to get it to quickly (milliseconds) switch from the 5 to 2.4 Ghz SSID. I used the Network Analyzer app to view the currently connected BSSID in real time, and turned off the cellular radio. In my backyard even with a single "bar" of signal, being about 100' from the router, and completely trying to block the signal with my hands and body, I could never get it to switch or drop the 5 Ghz signal. I then took a slow walk down the street - after about 4 houses down the street the signal completely dropped. Upon walking back it connected to the 2.4 Ghz signal.

The problem is when I turn the cellular radio back on, often it will switch to LTE rather than the 2.4 Ghz radio. Turning off Wi-Fi Assist solved that issue.

Ultimately I think I will be waiting for Wi-Fi 6E and the support for 6 Ghz channels, then get a mesh system that supports 802.11k/r/v placed at opposite ends of the house.

 

[thiggins]

Ultimately I think I will be waiting for Wi-Fi 6E and the support for 6 Ghz channels, then get a mesh system that supports 802.11k/r/v placed at opposite ends of the house.

6E could help or hurt, due to range differences. What the differences will be are still TBD.
Even with k/v/r, unless your phone also supports them, you may not achieve your goal. It generally takes purpose-built devices and networks to achieve sub-second roam times.

 

[MichaelCG]

Don't think you can avoid WiFi call drops or pauses when roaming on consumer gear. I have multiple APs across my house and in general, my iPhone and my laptop will roam around with no impact....except for voice calls. Depending on the app, it may just be a 2-3 second pause in audio while some just drop. If you want rock solid coverage, stick to a centrally located 2.4GHz setup and never roam. That will however punish overall performance if doing anything that is bandwidth intensive.

I try to not roam across the entire house when on a call for the most part. Or I just warn the other party I am moving around and give me a second for the voice stream to recover. This is generally why I don't let my iPhone use WiFi calling at home.....as well as there are additional challenges with voice volume. I am lucky enough to have good cell coverage at my house, including my basement.

 

[mjc775]

6E could help or hurt, due to range differences. What the differences will be are still TBD.
Even with k/v/r, unless your phone also supports them, you may not achieve your goal. It generally takes purpose-built devices and networks to achieve sub-second roam times.

I would guess 6E propagation wouldn't be much different than 6 considering the new channels start only ~100 Mhz above the current top frequency of 5.8 Ghz.

Fortunately the latest iPhones support the roaming standards: https://support.apple.com/en-us/HT202628

I did another test today where I was able to attenuate the signal enough in my backyard to get my iPhone 11 to switch from the 5 to 2.4 Ghz network. It definitely wasn't fast enough for a Wi-Fi call to hold, but acceptable for web browsing. I think the key for switching to the stronger 2.4 Ghz Wi-Fi signal instead of LTE was making sure Wi-Fi Assist is turned off - otherwise it seems to favor switching to LTE before looking for a better Wi-Fi signal.

 

[thiggins]

I would guess 6E propagation wouldn't be much different than 6 considering the new channels start only ~100 Mhz above the current top frequency of 5.8 Ghz.

That was my initial conclusion, too. But allowable indoor power level details released by the FCC when approval was announced make me uncertain at this point.

6E sets allowable transmit power in terms of spectral density. Full power is allowed in a 320 MHz channel bandwidth (not actually allowed in 11ax or 6E; it's coming in 11be). Allowed power level then DECREASES as channel width decreases.

 

[mjc775]

Allowed power level then DECREASES as channel width decreases.

Interesting, but makes sense to lessen co-channel interference. I'm tired of seeing my neighbor's routers polluting the airwaves using 80 and 160 Mhz wide channels when I know their internet speed is only ~100 Mbps, and I doubt they're frequently transferring large files across their wireless network.

EDIT: I just re-read this. This makes no sense to decrease airwaves pollution - or am I missing something here?

 

[thiggins]

EDIT: I just re-read this. This makes no sense to decrease airwaves pollution - or am I missing something here?

I agree this is confusing. Please read this excellent Sniff WiFi blog post, Facts #3 and #4.

If his analysis is correct, 2.4 GHz, 20 MHz channels could see a noticeable range reduction. But range loss for 5 GHz, 80 MHz channels could be minimal.

 

[coxhaus]

Don't think you can avoid WiFi call drops or pauses when roaming on consumer gear. I have multiple APs across my house and in general, my iPhone and my laptop will roam around with no impact....except for voice calls. Depending on the app, it may just be a 2-3 second pause in audio while some just drop. If you want rock solid coverage, stick to a centrally located 2.4GHz setup and never roam. That will however punish overall performance if doing anything that is bandwidth intensive.

I try to not roam across the entire house when on a call for the most part. Or I just warn the other party I am moving around and give me a second for the voice stream to recover. This is generally why I don't let my iPhone use WiFi calling at home.....as well as there are additional challenges with voice volume. I am lucky enough to have good cell coverage at my house, including my basement.

I have no problem with Wi-Fi roaming using an iPhone with my Cisco WAP581 wireless APs. I have a test I perform for roaming. I have my wife on the back AP and me on the front AP. I call her on her iPhone using my iPhone. I walk to her AP and past just to make sure I roam. I am talking the whole time to see if I lose part of the conversation while I am roaming during a Wi-Fi call. This seems to be the hardest roaming test I can come up with.

 

[mjc775]

...should the iPhone more quickly/easily roam to the 2.4Ghz network using the same SSID or a different SSID? Or should there be no difference?

When trying to get my iPhone to choose one SSID over another, I may have discovered the trick. I've got two 5Ghz SSIDs - one starting with M, the other starts with N. Whenever I get home after leaving the house, it always connects to the M SSID. Therefore it seems with all other things being equal - like signal strength and band - it connects to the saved networks in alphabetical order.

 

[thiggins]

Therefore it seems with all other things being equal - like signal strength and band - it connects to the saved networks in alphabetical order.

This is most likely coincidence. Clients identify APs by BSS (MAC address). SSID's can be set network-wide, so can't be used to identify a specific AP.

 

[mjc775]

^^ It’s an uncanny coincidence. The M network’s MAC ends in :cf - which I believe comes after the N network’s :c8 in the hexadecimal numbering sequence. So I’m left to wondering why it selects one SSID/MAC over another with signal and band being equal. Maybe Steve Jobs knows - so we’ll never know.


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[degrub]

macs of any flavor always try to connect with the last network associated.
The list under networks determines the order after that.

 

[mjc775]

^^ Unfortunately I don’t believe we can access that list, nor change the order in the Apple environment.


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[coxhaus]

What works for me with my iPhones and iPads well is to use both 2.4 and 5 GHz on the same SSID. This way as I walk out into the back yard my iPhone just switches from 5 to 2.4 GHz as 5 GHz does not go vary far in my back yard.

I have 2 Cisco WAP581 wireless APs setup with both 2.4 and 5 GHz on the same SSID. I have 2 SSIDs one for guest and one for LAN which are separate VLANs that run to both APs.