Draytek Vigor2500V Manual page 123

12.2.3 CODEC/RTP/DTMF Setup
Default Codec: Select one of five CODECs as the default for your VoIP calls.
The CODEC used for each call will be negotiate with the peer party before
each session, and so many 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
Packet Size: The amount of data contained in a single packet. The default value
is 20 ms, which means the data packet will contain 20 ms voice information.
DTMF InBand: With this selected the Vigor will send DTMF tones as audio
directly in the Voice stream when you press a key on the keypad.
DTMF OutBand: With OutBand selected the Vigor will capture the keypad
number pressed, transform it to a digital form and send to the other side
outside of the Voice stream; the receiver will generate the tone according to
the digital form it receives. This function is very useful when network traffic
congestion occurs to maintain the accuracy of DTMF tones.
DTMF Payload Type: The default value is 101, but can be anything from 96 to
127.
SIP INFO: Enable this option to let the SIP proxy send DTMF tones to the dialed
peer.
RTP: Specifies the start and end port for RTP stream. The default values are
10050 and 15000
VoIP
.
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