[8.270][BUG][NOT A BUG] Ap50 roaming delay

[Eberwein]

O.K. let´s say sometimes it is nearby 1s when you roam on the same band.
Or is the roaming between 5Ghz and 2Ghz at your side 1s?

But I think the time is almost to long. A litte crack in the line on a call would be O.K. but a silence from let´ s say nearby 1s is to long.

best regards
Volker

[hschaa]

To summarize:
It doesn't matter if you use WPA-PSK or WPA-EAP. The roaming delay is nearly the same. Hence, the roaming delay is most likely not introduced by the EAP authentication but by the scanning for a better AP or something else.

To track this down you could place two APs (doesn't matter if AP30 or AP50) in range onto the _same_ channel (for example two AP50s on channel 48). Then configure the phone to _only_ scan this channel and retry if the roaming speed improves.

The WPA handshake itself should be way shorter then 100ms. And since both APs are on the same channel the scanning delay shouldn't happen at all since the 7925 doesn't have to scan different channels.

It would be very helpful to know what exactly is introducing this delay.

Thanks again,
Helmut

[hschaa]

Oh, and could you please check what "scan mode" your phones are using, as described in
Cisco Unified Wireless IP Phone 7925G and 7921G Release Notes for Firmware Version 1.3(4) - Cisco Systems ?

[hschaa]

Could this explain the roaming delay between 2,4Ghz and 5Ghz bands?

Before firmware release 1.3(4), both bands would be scanned only at power up or if the current band was lost if configured for an Auto 802.11 mode. Because of this, there was no seamless roaming since the current band would have been disconnected before the target band could be discovered. Also, there was a possibility that the phone could stay connected to the less preferred band (i.e. connected to 2.4 GHz when it is configured for Auto-A mode and a good 5 GHz signal is available).

[Eberwein]

My phone has a skinny Firmware with Version 1.3.3. This maybe the Problem for roaming between 2Ghz and 5Ghz. I will look for an update.
I made some more tests in my company environment. In other locations and when I roam only on one band it´s partial o.k.(short silence on a call)
But I will recheck this some times more.
I also do some tests with the AP10, and now, I removed them from my Network...
I removed 4 AP10 and and installed for them 2 AP50! The range and quallity of the signal is much better. I also tested other antennas on AP10, but the AP50 is really much better.

So what can I say:
I think the environment takes big care for the roaming delay.(electrical noises, signal reflektions,...)
The speech quallity of a call is on 5Ghz better (opinion of me and my colleague).
When there is a lot of metall near the phone it is like you talking through a can.
Signal range and quality of an AP50 is much better as of an AP10

[Eberwein]

I have now Firmware CP7925G-1.4.1SR1 on the phone, hand it seems pretty good.
Roaming between the same band and other band work fine (only little silence).
In hard wireless environments (disruption by electricity, metall etc...)there are still problems with longer breaks between roaming.
So I can say the main Problem was the phone Firmware and configuration.
I found also two options on the phone that may improve the roaming:
Surplus Bandwidth (set to 1.300000)and Minimum PHY Rate (set to 12Mb/s)
Do you have an idea of good settings for this options

regards

[hschaa]

Originally Posted by Eberwein

I have now Firmware CP7925G-1.4.1SR1 on the phone, hand it seems pretty good.
Roaming between the same band and other band work fine (only little silence).
In hard wireless environments (disruption by electricity, metall etc...)there are still problems with longer breaks between roaming.
So I can say the main Problem was the phone Firmware and configuration.

Nice, thanks for the info!

Originally Posted by Eberwein

I found also two options on the phone that may improve the roaming:
Surplus Bandwidth (set to 1.300000)and Minimum PHY Rate (set to 12Mb/s)
Do you have an idea of good settings for this options

I don't know what Surplus Bandwidth is meant to do but the minimum phy rate of 12Mbps looks reasonable to me.

Typically a lower phy rate has a "stronger" and more "stable" signal and thus this would increase the maximum distance from the AP. On the other hand, a lower phy rate is more prone to disruptions (like electrical disruptions in your case). Furthermore a lower phy rate consumes more airtime and thus the overall wifi capacity will be reduced.

So, if your APs are close enough to each other such that a minimum phy rate of 12Mbps is enough (which seems like it is in your case) to not lose connectivity between two APs I wouldn't use a lower value.

This is quite old already but has a nice rate-vs-range graph in it:
The Range vs. Rate Dilemma of WLANs

Thanks again,
Helmut

[Eberwein]

What I can find out is that Surplus Bandwidth is a kind of QOS.
It mean that you can allocate some Bandwith for pre roaming or something like this
(function that belongs to the IEEE802.11e standard).
Please correct me when I wrong!!!

[hschaa]

Correct, that's part of 802.11e but it's optional and would allow the AP to make better assumptions about the expected client traffic but we don't use it in the AP10/30/50 yet. So, it should have no influence on the roaming behavior.