webrtc - What are ICE Candidates and how do the peer connection choose between them?

Question

I newly wrote a simple chat application, but I didn't really understand the background of ICE Candidates.

When the peer create a connection they get ICE Candidates and they exchange them and set them finally to the peerconnection.

So my question is, where do the ICE Candidates come from and how are they used and are they all really used ?

I have noticed that my colleague got less candidates when he executes the application on his machine, what could be the reason for different amount of Candidates ?

Answer 1

the answer from @Ichigo is correct, but it is a litte bit bigger. Every ICE contains 'a node' of your network, until it has reached the outside. By this you send these ICE's to the other peer, so they know through what connection points they can reach you. See it as a large building: one is in the building, and needs to tell the other (who is not familiar) how to walk through it. Same here, if I have a lot of network devices, the incoming connection somehow needs to find the right way to my computer. By providing all nodes, the RTC connection finds the shortest route itself. So when you would connect to the computer next to you, which is connected to the same router/switch/whatever, it uses all ICE's and determine the shortest, and that is directly through that point. That your collegue got less ICE candidates has to do with the ammount of devices it has to go through. Please note that every network adapter inside your computer which has an IP adress (I have a vEthernet switch from hyper-v) it also creates an ICE for it.