Draytek Vigor2920 Series User Manual page 245

NAT Traversal Support
Ring Port
Ring Pattern
Prefer Codec
If the router (e.g., broadband router) you use connects to
internet by other device, you have to set this function for your
necessity.
None – Disable this function.
Stun – Choose this option if there is Stun server provided for
your router.
Manual – Choose this option if you want to specify an
external IP address as the NAT transversal support.
Nortel – If the soft-switch that you use supports Nortel
solution, you can choose this option.
Set Phone 1 and/or Phone 2 as the default ring port(s) for this
SIP account.
Choose a ring tone type for the VoIP phone call.
Select one of five codecs as the default for your VoIP calls.
The codec used for each call will be negotiated with the peer
party before each session, and so may not be your default
choice. The default codec is G.729A/B; it occupies little
bandwidth while maintaining good voice quality.
If your upstream speed is only 64Kbps, do not use G.711
codec. It is better for you to have at least 256Kbps upstream if
you would like to use G.711.
Single Codec – If the box is checked, only the selected Codec
will be applied.
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Vigor2920 Series User's Guide