The sipXcom proxy includes built-in compensation for both near and far end NATs (sipXrelay, also known as Media Relay), and sipXbridge (handles trunking) provides what you need to connect to external SIP Trunk services.
If you are really serious about SIP trunking and NAT traversal an external SBC is strongly recommended.
The aforementioned are known to work but you may want to trial with your installation. They have a few limitations:
- sipXbridge may not work with all trunking providers (Asterisk based providers have troubles with the SIP messaging around REFERs and cause issues on call transfers)
- sipXbridge won't scale well beyond 75 or so concurrent calls
- sipXbridge and sipXrelay do not work properly in a HA setup.
The following SBC's are known to work to varying degrees with sipXcom. Try before you buy (if you can).