WebRTC doesn't proscribe a signalling mechanism at all. SIP is sometimes used, Jingle (XMPP) sometimes, or sometimes it's just a custom protocol exchanging SDPs (or equivalent structures) over WebSockets or a REST API.

WebRTC itself is RTP (DTLS-SRTP), ICE (incl. STUN/TURN), codecs & related parameters, capture mechanisms, all bundled up into a Web API.