bss-minrate vs. smart-roam

[jeff_roback]

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

[bill_burns_6069]

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".

[sid_sok]

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.

[primoz_marinsek]

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.

[bill_burns_6069]

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)