The App uses ipv6 link local addresses (fe80::.. + mac address). But it also tries to make use the received IPv6 network prefixes. Also, the last contact address is stored. These approaches improves the probability a bit to find the contacts in other networks.
As a side note, many mesh networks are emulating a layer 2 network. With this, everybody can build up their own decentralized telephone network.
I also now of this Android App that uses WebRTC Audio/Video without server (no Internet or DHCP needed): https://github.com/dakhnod/Meshenger
I made a submission, in case somebody likes to discuss the need for serverless WebRTC: https://news.ycombinator.com/item?id=18203495
(Disclaimer: I am not the author of the App, but I helped out a bit)
An Android App that allows Audio/Video communication without need for Internet, DHCP or IPv4. It connects to common wireless Access Points. Contacts are exchanged via QR-Code.Works on home, company and mesh networks.This project is meant more or less as a demo that this can be done.Link: https://github.com/dakhnod