bss-minrate vs. smart-roam

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Looking for some clarification of the impact of bss-minrate vs. smart-roam (as well as some best practices on setting them). Is it an issue of one controlling the minimum rate to join the network, and the other controlling the minimum rate before getting kicked off?

One issue we've started to see is that iphones will 'hang on' to the ruckus signal for too long. So at one client location, for example, the café across the street from their office still gets a very weak ruckus signal... strong enough for laptop usage, but not strong enough for iphones to reliably pass data, but strong enough that the iphone won't let go... so when people walk across the street for lunch, their iphone doesn't switch to 4G, it just hangs on to the barely connected wifi and the users get no data. Would smart-roam+bss-minrate be the appropriate fix for this?

Also, any suggestions on rates to use for these two commands?

Thanks!
Jeff
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Jeff Roback

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Posted 4 years ago

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Bill Burns, AlphaDog

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Smart-roam exists to deal with the "stuck client" issue. (that you're describing)
bss-minrate can have a similar effect.

If you have an AP in a high location (or that otherwise has good RF visibility over a large area) most wifi clients will not dis-associate from the AP until their signal strength (RSSI) is very low.
I have seen examples where you can walk past 2 or 3 buildings (each with their own APs) without dropping an established association from an AP w/ a "good" coverage area.
Loss of connectivity can occur, where the client still sees "good" RSSI and will refuse to drop the association. (no pings go through, etc)

What smart-roam does is check (from the AP side) for RSSI (or maybe SNR?) and stops responding to any client below a certain threshold. This "encourages" the client to roam, and associate with a closer AP.

This can also limit the efective range of the AP so it blunts some of the advantages of Ruckus' superior RF power. (EIRP)
..especially for APs that are in more challenging areas.

What bss-minrate does is put a lower limit on the data-rate at which an AP will associate with a client.
The idea here is that if the client has poor connectivity and wants to step-down to a lower data rate to improve the situation, it won't be able to and that will "encourage" the client to decide to roam.

With smart-roam (if you want to use it) a good value to start with is "5".
(larger numbers make the APs stop responding earlier)
With bss-minrate, a good number might be "12".
YMMV.

For good measure, you could try ofdm-only.

In some situations (with a large number of ruckus APs) another solution might be to relocate an especially problematic AP with a good "view" to another location with a worse RF "view".
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Sid Sok, Official Rep

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Hi Jeff,

The two are not mutually exclusive.

Smart-roam without the BSS-minrate will keep track of client RSSI and if it hits the threshold it will kick the client off, ideals the client it in a an area that another AP will provide a better signal, so the client then is looking for a new and better AP and that should be the AP with the stronger signal, but if the signal level is not all that different and the client driver has a preference to connect to the last known BSSID it will most likely connect back to the same Access point. The APs keeps a lot of metric on the clients and uses internal response timer to try to encourage the client to make the right choice, but it's the client's decision.

BSS-minrate will effectively reduce the coverage area, in that the beacon as well as other management frames at a higher data rate will not go as far as a lower data rate frame.

You can have over laps. For example of you set SmartRoam to a low value 1 (SNR/RSSI threshold of 5) and you set the BSS minrate to 12 Mbps, you will get out of range of the AP's 12 Mbps Beacon range way before you would hit the 5 dB RSSI for a SmartRoam of 1, so your client will disconnect from the old AP (out of range) and connect to a new one assuming there is another AP that the client can hear at 12 Mbps, before SmartRoam is triggered. You can have it the other way around as well, If you set SmartRoam to 10 which requires that the client SNR be 60 dB above noise and you the BSS minrate set to 6 Mbps, you will hit the SmartRoam threshold before the client get out of the 6 Mbps range.

As for the threshold recommendation, it will really depend on the coverage. If the deployment were designed for (lower band) 5 GHz coverage of -65 dBm or better everywhere, then you can start with either the SmartRoam of 5 (SNR/RSSI=20 dB) or if you wan to use bss minrate you can start with 12 Mbps. From there you can adjust either to optimize for the environment. That is assuming the the coverage is uniform, if not use the value appropriate to the area with the sparse coverage area.
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Primož Marinšek, AlphaDog

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Maybe in this case setting bss-minrate to 12Mbps might be usefull, however I wouldn't suggest it globally as the preamble is always sent at 6Mbps for ERP-OFDM and OFDM or rather at minimum PHY speed.

I would rather suggest you set your AP to use OFDM only and leave minrate at 6Mbps, then play with smart-roam.
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Bill Burns, AlphaDog

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Thanks for the correction/clarification Sid.
(re: smart-roam shouldn't really limit the range since it allows a client to re-connect, where bss-minrate wouldn't)
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Sid Sok, Official Rep

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Hi Bill,

We almost had a posting collision. I started the answer a few hours before I posted, but was interrupted along the way and did not see your post until later. Glad everything lined up. Reading from the top my response it does look like I was responding to your post, but it was originally meant as a response to Jeff, but it dove tail perfectly to your post.
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Jeff Roback

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Thanks guys, this is tremendously helpful! A question: the SNR/RSSI values your're referring to, are these directly comparable to the ones that we see in the "Active Clients" list, or do they need to be cpnverted?

Looking at one client install now, I've got about 100 users an average signal (db) in the currently active clients window listed as 30 db, and about 11 under 20 db. So if I set the smartroam to 5, would I expect those 5 clients to disconnect and hopefully look for a closer AP?

Jeff
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Bill Burns, AlphaDog

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re: "Active Clients"
Right. If you see a column called "signal%" and click on it, it will change to "Signal (dB)" Those are the RSSI/SNR values.

re: would I expect those clients to disconnect:
Yes.
Especially... if those clients have an RSSI/SNR (as seen by the AP/controller) of *over* 20db and *then* "walked" to an area where the RSSI/SNR was less than 20db, the AP should stop responding to the client and the client should disconnect. (and hopefully find a closer AP)
If the client does not find a closer AP, it may reconnect to the same AP.
At that point, the AP "should not" try to disconnect the client any more.

It would make sense to test this in your environment.
(if you have enough cooperating users/devices)
One thing I might be concerned about is natural fluctuation in the RSSI/SNR values.
If those values are "riding the edge" and there isn't a better AP to connect to...
I wonder if the client *could* be repeatedly disconnected.

The AP is supposed to be smarter than that.
It'd be good to know for sure.
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Jeff Roback

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got it. Will do more testing.

Is there any way to know from the AP or ZD logs when the bss-minrate or smart-roam functionality is engaging? I've started seeing these in the logs:

User[xx:xx:xx:xx:xx:xx ] fails to join WLAN[xxxx] from AP[DMB-AP-2]

And we also continue to see log entries for a client roaming from and AP and then roaming out to the same AP. Is that a case of the AP not responding and the client re-connecting?

And here's a really odd one (may need a new thread for this): Take alook at this roaming:

2014/01/17 16:50:03 Low AP[CORP-AP-1] radio [11g/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams out to AP[CORP-AP-2]
2014/01/17 16:50:03 Low AP[CORP-AP-2] radio [11g/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams from AP[CORP-AP-1]
2014/01/17 16:50:16 Low AP[HB-AP3] radio [11a/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams out to AP[HB-AP1]
2014/01/17 16:50:16 Low AP[HB-AP1] radio [11a/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams from AP[HB-AP3]
2014/01/17 16:50:19 Low AP[CORP-AP-2] radio [11g/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams out to AP[CORP-AP-1]
2014/01/17 16:50:19 Low AP[CORP-AP-1] radio [11g/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams from AP[CORP-AP-2]
2014/01/17 16:50:57 Low AP[HB-AP1] radio [11a/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams out to AP[HB-AP3]
2014/01/17 16:50:57 Low AP[HB-AP3] radio [11a/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams from AP[HB-AP1]
2014/01/17 16:52:55 Low AP[CORP-AP-1] radio [11g/n] detects User[xx:xx:xx:xx:xx:xx] in WLAN[MyWLAN] roams out to AP[CORP-AP-2]

Doesn't look to bad at first... until you realize that the "HB-AP's are in one location, and the CORP-AP's are in another location a mile away.....

What could be doing on here?

Jeff
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Keith - Pack Leader

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This is a great conversation that's separate from the main topic, so I created a new topic to continue the discussion. Please reference the new topic here: Is there any way to know from the AP or ZD logs when the bss-minrate or smart-roa...
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DSE

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Hello, any suggestion or best practice for using smart roaming and Bss-minrate when using  802.11r FT Roaming ?