WIFUND -9- WLC and AP concepts

So here we are, our WLC is up and running, also some APs and a lot of hungry clients, waiting for a connection.

The first we need to talk about is SPLIT MAC. This concept means that in a controller based WiFi-network a lot of tasks are moved from the AP to the controller.
That’s great because the controller makes it muuuuuuch easier for us, no one wants to configure 100 APs one by one.

In fact the WLC takes over the complete processing of the packets, dis-/association, authorithation, policys, frequency management and so on. The AP, on the other hand, concentrated at the radio functionality and also:
– Any real time traffic (sending beacons, probes and ack’s)
– Manage the RTS/CTS

Do you know old telephony systems with the legacy DECT-radios which are directly connected to a line-card of the PBX (for example an Siemens HiPath and the BS4 radios)? Virtually there is affinity as the WLC it does.
Because the WLC manages the AP and also need the data-traffic for processing there are two types of virtual cables aka tunnels, between the AP and the WLC. Please do not beat me 🙂 , it’s the way I best save this into my brain.
In old telephony systems the DECT-radios are directly connected to the PBX and the are a part of this, like router at home with buildin WiFi – it’s also part of the device.

But our AP is a very happy standalone device, with it’s on IP and config. The WLC is so sad, because he want to serve you with WiFi, but without any radio, no way.
So let’s connect the AP to the WLC like an old DECT-radio to a PBX:
First we need a cable to control the AP, tell it what to do, especially send the config or also the AP send back things like which other APs it see’s. That’s our control cable. Next we need a cable for the data-flow of our wireless-clients. Because not the AP should process this, it’s a job for the sad WLC to make him more happier. This is the second cable, the data-cable. STOP!!! But hey, we don’t need a dedicated cable or so on, because the AP and the WLC are talking via IP, we use the IP-network to connect them.
This is done with CAPWAP (Control and Provisioning of Wireless Access Points).
But whats this? In my brain I saved it up as a „tunnel“ between the WLC and the AP, like a VPN tunnel, it’s also encapsulated.