Draytek Vigor2920 Series User Manual page 247

Item
RTP
Description
Default SIP Account – "draytel_1" is the default SIP account.
You can click the number below the Index field to change SIP
account for each phone port.
DTMF Relay – Display DTMF mode that configured in the
advanced settings page of Phone Index.
Symmetric RTP – Check this box to invoke the function. To
make the data transmission going through on both ends of local
router and remote router not misleading due to IP lost (for
example, sending data from the public IP of remote router to
the private IP of local router), you can check this box to solve
this problem.
Dynamic RTP Port Start - Specifies the start port for RTP
stream. The default value is 10050.
Dynamic RTP Port End - Specifies the end port for RTP
stream. The default value is 15000.
RTP TOS – It decides the level of VoIP package. Use the drop
down list to choose any one of them.
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Vigor2920 Series User's Guide