How do two phones make a WebRTC voice call without internet?
WebRTC normally uses an internet server to exchange SDP offers and ICE candidates before connecting two devices. How does QR code signaling allow two phones on the same mobile hotspot to connect with zero cellular data?
Verified Community Answers (1)
Devon Brooks • 118 upvotes
WebRTC only needs a signaling channel for the initial handshake (exchanging the SDP Offer and SDP Answer containing local LAN IP addresses and audio codecs). By encoding the compressed SDP into a QR code on Phone A and scanning it with Phone B camera (and scanning Phone B answer QR back), both browsers establish a direct local UDP media stream over the Wi-Fi hotspot router without ever touching the internet!