NAT and VoIP
The way in which conventional VoIP protocols are designed is posing a problem to VoIP traffic passing through NAT (Network Address Translation). Conventional VoIP protocols only deal with the signaling of a telephone connection. The audio traffic is handled by another protocol and to make matters worse, the port on which the audio traffic is sent is random. The NAT router may be able to handle the signaling traffic, but it has no way of knowing that the audio traffic is related to the signaling and should hence be passed to the same device the signaling traffic is passed to. As a result, the audio traffic is not translated properly between the address spaces.
At first, for both the calling and the called party everything will appear just fine. The called party will see the calling party’s Caller ID and the telephone will ring while the calling party will hear a ringing feedback tone at the other end. When the called party picks up the telephone, both the ringing and the associated ringing feedback tone at the other end will stop as one would expect. However, the calling party will not hear the called party (one-way audio) and the called party may not hear the calling party either (no audio).
The issue of NAT traversal is a major problem for the widespread deployment of VoIP – however, one of the servers implementing IETF’s Best Current Practices for NAT traversal for Client-Server SIP is Yate which is integrated with AVAVoIP.
Media routing
To optimize bandwidth usage, avoid latency issues, and minimize costs you may want to allow the media (RTP) portion of a call to be routed directly between the far endpoints, rather than routing it through the switch. On the other hand for endpoints behind NAT it is recommended to force the switch to route the media in order to avoid the potential no audio or one-way audio issues described above.
The platform allows tuning of media routing at three levels:
- Accounts » Access » Endpoints
- Routing » Endpoints » Update Carrier Endpoint
- Yate AVAVoIP routing configuration file
Accounts » Access » Endpoints » “Route Media”
If checked AVAVoIP will force the switch to route the media for traffic in/out of the Endpoint.
Routing » Endpoints » Update Carrier Endpoint » “Proxy Media”
If checked AVAVoIP will force the switch to route the media for traffic in/out of the Endpoint.
Yate AVAVoIP routing configuration file
You can use options media_route and media_route_on_nat in Yate AVAVoIP routing configuration file to configure media routing.
Option media route will force all media traffic to be routed via Yate by default.
If you use option media route on NAT the system will try to detect NAT from RTP addresses and force media routing via Yate
Please note that routing the media directly between the endpoints prevents topology hiding and may cause business or security issues depending on the setup.
Please contact us for more information about these issues.