Regarding SIP ALG
Almost all routers include a feature called SIP ALG, and are delivered with this feature enabled by default.
An Application Layer Gateway, or ALG, could help in solving NAT related problems, but in our experience, most ALG implementations are wrong and break SIP.
Leaving SIP ALG enabled not only breaks SIP functionality, but can also impact the RTP audio stream resulting in one-way audio where you can hear the caller, but they can't hear you, or vice versa.
You should disable SIP ALG and configure either port triggering or one-to-one port mapping on the router as appropriate.
If you use a Sonicwall Firewall, there are a few simple changes that will need to be made in order to allow the device to work with our service. Although different versions of the Sonicwall operating system may have these settings in different places, the following steps will ensure your device will function properly.
The VoIP Tab
- Start by accessing the device's web interface. To do this, enter the router's IP address into your browser. Usually, this is 192.168.1.1.
Username: admin
Password: password - Go to the VoIP tab, or Firewall > VoIP, depending on the device's operating system.
- Near the top of the page, make sure Enable Consistent NAT is ticked.
- Further down on the page, make sure Enable SIP Transformations is unticked.
