User guide
28
SETTINGS
VAD
Voice Activity Detection (speech detection) is a technique used in speech processing to
detect the presence or absence of human speech in regions of audio. In VoIP applications,
VAD is mainly used to avoid unnecessary coding and transmission of silence packets,
saving on computation and network bandwidth.
On phone: MENU > SETTINGS > ADVANCED > (PIN) > MEDIA > VAD (6,2,4,2).
DTMF
DTMF (Dual-tone multi-frequency) signalling is used for telephone signalling over the line
to the phone switch or PBX.
If the device itself generates the tones and they are sent in the voice-frequency band, the
method is called Inband. This is not the best method when using VoIP. Low bit rate co-
decs may corrupt the signalling tones and make it difcult for the switch to identify them.
RFC 2833 is a method of carrying DTMF signals in RTP packets using a separate RTP
payload format. With this method a PSTN gateway reproduces the DTMF tones sent from
the end device.
With SIP Info the DTMF signals are sent as SIP requests. The SIP switch creates the
tones if the call is transferred to the PSTN.
Use RFC 2833 or SIP Info as preferred methods. Switch to inband only if you encounter
problems using DTMF signalling with your PBX/SIP switch.
On phone: MENU > SETTINGS > ADVANCED > (PIN) > MEDIA > DTMF SIGNALLING (6,2,4,3).
Advanced
First RTP port If the RTP packets must be directed to a specic port series, the
rst port number is set here.