Client switchover time when AP fails

[Michiel Vercoutter]

Hello,

I have a customer demanding very short downtime on clients connected to an AP that fails/disconnects. When an AP fails, the clients connected should switch to another AP in less than 1 second. Is this even possible?

From what I understand, the reconnecting process goes like this:
1. Client has to become aware that he lost connection to the AP (I don't exactly know how but I know it takes some time)
2. Client scans (with probe requests) all channels (some clients allow setting the channels, and smaller amount of channels results in lower scanning time, but I don't think this can be done in every environment)
3. Client receives probe response from an AP and has to go through the process of authentication and reassociation

Can the process above be sped up in any way? In my testing, clients lose about 3-4s of pings, and Webex/Whatsapp calls take 6-9s to reconnect, but apparently this is not enough, even though the chanse is very small that an AP disconnects, let alone that the client is connected to that exact AP and sending data at that exact time.

I know 802.11k/r helps with roaming, but could it maybe also help with this?

Thanks in advance.

[Leo Laohoo]

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@Michiel Vercoutter wrote:

When an AP fails, the clients connected should switch to another AP in less than 1 second. Is this even possible?

From what I understand, the reconnecting process goes like this:
1. Client has to become aware that he lost connection to the AP (I don't exactly know how but I know it takes some time)
2. Client scans (with probe requests) all channels (some clients allow setting the channels, and smaller amount of channels results in lower scanning time, but I don't think this can be done in every environment)
3. Client receives probe response from an AP and has to go through the process of authentication and reassociation

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If the wireless client has up-to-date wireless drivers, yes, this is very possible.  

I see this all the time with wireless VoIP handsets.  Users are on the handsets and they walk, as in REALLY, REALLY ROAM.  They jump from one AP to another, and another, and another.  The call continues.  No drops.  

[Michiel Vercoutter]

Thank you for your reply.

Client has latest Intel AX200 drivers.

I'm more asking about the difference between normal roaming and roaming caused by a failing/disconnecting AP, and how to speed up this process

[patoberli]

It also depends on your encryption and if you have features like CKIP and stuff like that enabled/disabled. This again depends on the used clients.
But a normal WPA2 with AES can be very fast. One important thing is to have enough overlapping coverage, but not to much :) Wireless site-survey is needed for that.

[Scott Fella · Accepted solution]

This is more of a device function than an access point function. An AP fail is like having two AP's at home and while connecting to one AP, you unplug it so it looses power. The device has to detect that the ap is no longer there, then perform a scan and go through the whole association process. Every type of device might handle this differently and your results will vary. Disconnect an Ethernet cable from the wall and connect it back, that process is faster, but still takes over 1 second.