I stir up controversy every time I say this, but I will say it anyway. WebRTC does not define a signaling protocol. This means that developers are free to use whatever method or protocol they want when they create their solutions.
In my latest article for No Jitter, I introduce my readers to the AudioCodes WebRTC gateway and its ability to connect “pure” WebRTC calls with legacy communications systems.
Tao, Zen, and Tomorrow 