Via, Contact and NAT: Three SIP Addresses I Kept Mixing Up
NAT problems became easier once I stopped treating every SIP URI and IP header as the same kind of return address.
NAT
NAT Overload Made More Sense When I Looked at the Translation Table
PAT stopped feeling like a magic Internet-sharing feature once I watched inside local addresses, public translations and transport ports change in the NAT table.
RTP Relays Made Container Boundaries Easier to Control
Anchoring media at a deliberate boundary reduced the number of private addresses that leaked into SDP and simplified firewall policy.
SIP Registration Expiry Explained Why Phones Disappeared After a While
A successful REGISTER is temporary state, so expiry, refresh timing and NAT mappings all matter if an endpoint is expected to remain reachable.
One-Way Audio Is Usually a Directional Problem
If one side hears audio, several parts of the media path are already proven.
The Call Connected but Only One Side Had Audio
One-way audio was my first VoIP problem where the signaling looked healthy and the real fault was the address and port information used for RTP.