Control Slots - Can someone explain this dark art?

Alright guys, long time lurker, first time poster.

One thing I have yet to hear explained well is the meaning/function/use of Control Slots.

Can anyone shed some light on this subject for me? It would be much appreciated.

I’m going to attempt at explaining this so please someone barge in if I am wrong.

When APs & SMs communicate between each other, only 1 radio can be sending info at any given time (whether it be an AP or SM).

Each SM basically is given a certain time slot as to when it can communicate back with the AP (these are microseconds so it’s not actually something you can see)
Now when a radio communicates, it has a certain amount of information in each packet that it has to send (timing info, destination, the actual data, etc.).

One of the pieces of information in the packet is a slot that tells when an SM can communicate with the AP.

The issue is that when your control slots are set to 0, only a certain number of SMs will have slots telling them when they can communicate.
So as you add more SMs, you have to designate more slots in the date packet so all the additional SMs can be given info as to when they can communicate back.

The downfall to this is that since there is only a certain amount of data that can be sent when a radio communicates, when you add more control slots it takes away from the available data that can be sent in the packet. So essentially it lowers the bandwidth a little bit (i believe a couple hundred kbps or so, but don’t quote me on that)

I know I missed something or am wrong somewhere on here so please someone else jump in.

One thing I have yet to hear explained well is the meaning/function/use of Control Slots.

Control slots are used for various AP/SM scheduling purposes. If you don't have enough, you'll find that you'll start seeing performance issues before actually running out of AP capacity.

Most people seem to set them to something like 3 or 4 across their entire network and forget them. Setting them to the same value ensures synchronization is the same since this is one of the parameters which changes when the AP's switch from transmit to receive.


Thanks for the info guys. So if all 20 of our 900 APs are set to 0 slots with each one having less than 40 subscribers each, will that become a problem as we add subscribers? Is there a guide line as to how many slots to use when?

Page 247 of the latest Canopy Manual,

1-10 users on AP: Set Control slots to 0
11-50 users on AP: Set Control slots to 1
51-150 users on AP: Set Control slots to 2
151-200 users on AP: Set Control slots to 3

Make sure if you change the control slots on 1 AP that you do it for all the APs in that cluster and any AP clusters close to that tower (best just to have all clusters set the same)

Thanks for the information guys. Much appreciated.