A "signal server" in this situation is any method that will allow the two end points to connect. However, you simply need to be able to exchange a few setup pac

A "signal server" in this situation is any method that will allow the two end points to connect. However, you simply need to be able to exchange a few setup packets. People used web sockets for this, but essentially anything that will exchange some information will work. see https://webrtc.org/getting-started/peer-connections https://webrtc.org/getting-started/peer-connections. There is a youtube video on writing a webrtc chat app and (during development) the developer simply copies and pastes between two windows on the same computer. Webrtc file transfer, text chat and video chat all use this information. In addition if one is negotiating connections across NAT servers you use STUN or TURN servers (there are open ones) to establish NAT. Your local computer/phone/whatever will send need to tell the other side what your NAT address is and STUN will do that.