how to setup a signaling server for webRTC when the system are connected in Local Area Network? Its mandatory that we must use STUN and TURN server for signaling?
Webrtc needs some kind of signalling system for initial negotiation.. like transferring SDP, ICE-candidates, sending and receiving offers etc... rest is done by peer-peer connection. For initial signalling you can use any technique like sending AJAX calls, using socket.io etc.
STUN and TURN servers are required for NAT traversal, NAT traversal is important because it is needed for determining the path between peers. You can use google provided STUN/TURN server address stun:stun.l.google.com:19302 etc , or you can configure your own turn server by using rfc-5766 turn server