#WirelessFriday – April 2017 – Questions & Responses

Thank you very much for your interest in the Cisco #WirelessFriday event!  This article is a quick recap of the April 2017 event with the associated questions and panel responses.  I would like to make a public thanks to Allan Ross for his presentation.

Cisco High Density Experience (HDX) Features Explained – Q&R

If you were not able to make the event live or if you just want to watch it again, you can catch the recording here.

Flexible Radio Assignment (FRA)

Q. If the RF profile is set to none on the AP group, does that disable that radio?
A. If RF Profile is set to none within the AP Group, APs within that group (for that band) will leverage whatever the global settings are of the WLC.

Q. So if I change the XOR to 5 gHz, I can assign different channels to each 5 gHz radio within the same AP?
A. Yes.  I would highly recommend you leverage Radio Resource Manager (RRM), which is a feature with the AirOS software running on a WLC, to automatically select the optimal channel for all the AP’s tied to your defined or default AP group.

In the setup where you are using the XOR radio to service 5 GHz clients, that radio has to be on a different channel to the one the fixed 5.0 radio is assigned.

Q. XOR is only available on 28xx and 38xx APs, correct?
A. Yes, That would be required. you end up with double the capacity in the 5 GHz band.

Dynamic Bandwidth Selection (DBS), FlexDFS (Dynamic Frequency Selection) & ED-RRM (Event Driven Radio Resource Management)

Q. Does CleanAir ED-RRM interact with RRM or do they remain separate local vs global processes, potentially causing a ripple effect and/or temporary co-channel interference?
A. They are separate processes, which is the reason why it is not recommended to mix CleanAir and non-CleanAir APs in the same RF neighborhood.

Q. What transmit power/data rate is used to determine coverage overlap? Same RRM neighbor beacons?
A. Correct, FRA leverages NDP output from RRM to evaluate COF. More details can be found here – http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-3/b_RRM_White_Paper/b_RRM_White_Paper_chapter_01000.html#id_29325

Adaptive Fast Transition (802.11r)

Q. Is “Roam Now” a command or a suggestion?
A. In the world of WiFi, the client rules. Some clients obey the “rules” you establish, while others do not.  Officially it’s a disassociation.

AirTime Fairness

Q. Can ATF and RF profiles be assigned to AP’s that aren’t in a AP Group?
A. RF Profiles must be applied to an AP Group. ATF can be applied to a WLAN, an AP individually, all APs connected globally, OR to an AP Group.

Q. How does ATF holdoff medium-contending clients, by not ACking frames?
A.  ATF can only enforce the downlink direction (the AP can control who it is sending to) – we can monitor usage in the uplink direction, but cannot specifically enforce it. Not ACKing frames would only result in excessive retransmissions.

Q. Please explain the differences in ATF and Override Per-User Bandwidth Contracts or SSID contracts
A. The Override Per-User contract in the QoS tab of the SSID enforces a bandwidth restriction, regardless of how fast they use it. ATF designates how much time they are allowed on the medium.

Q. Since ATF is applied at the AP or AP group would be assumed that this will work with Flex Groups
A. Yes, ATF is supported on either Local or FlexConnect mode APs.

Optimized Roaming

Q. What defines a proper site survey? Active? Passive?
A. An active SS requires the surveyor to inject RF signals. This is best done with an AP on a stand. You still need your survey tool, but as you walk the floor plan, you are also moving this AP on a stand to measure RF based on the placement of this AP.

There are common elements between a passive SS and an active SS. A passive SS surveys RF area that is already populated with Access Points. You will need a survey tool, like AirMagnet or Ekahau to measure RF signals at specific points.

Typically Active SS are needed for environments that do not have any RF in operation. You will need a scaled floor plan you desire to survey. With the survey tool in hand, you walk the area with frequent stops to take an RF measurement.






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