[a_subsystem]

>> sending a "SYN" packet in both directions at once.

Might be a totally dumb question but how does this work? Wouldn’t you already have to have communication to set a time?

[bscphil]

That's why protocols like this have what Wormhole calls a "mailbox server", which allows two ends separated by firewalls to do secure key exchange and agree upon a method for punching through directly. See also STUN: https://en.wikipedia.org/wiki/STUN