title UDP Hole Punching

A -> S: UDP ( from eAddrA : ePortA )
S <- B: UDP ( from eAddrB : ePortB )
note over S: obtain eAddrA and eAddrB IP addresses,\nthe external NAT ports ePortA and ePortB
S->B : info (eAddrA:ePortA)
S->A : info (eAddrB:ePortB)
A->B : UDP ( from eAddrA : ePortA )
note over A: A's NAT device adds an\nentry to its translation table
note over B: Drops packet since no entry in\nB's NAT's translation table yet
B->A : UDP ( from eAddrB : ePortB )
note over B: B's NAT device adds an\nentry to B's translation table
note over A: Accepts packet since there is\nan entry in translation table
A->B : UDP ( from eAddrA : ePortA )
note over B: Accepts packet since there is\nan entry in translation table