220.127.116.11 Connectivity Checks Phase Timer
After a Simple Traversal of UDP through NAT (STUN) binding request message and response are received from the peer, the Connectivity Checks Phase timer MUST be reset to 3 seconds. The firing of this timer signals the end of the connectivity checks phase. When this timer fires, the caller MUST pick the best candidate pair selected by the connectivity checks and send them to the callee. If no candidate pair is validated by the connectivity checks when the timer fires, the call MUST fail. Further connectivity check attempts MUST NOT be made after this timer fires.