AASTRA 480i User Manual

Advanced Network Settings

41-001129-00 Rev 09, Release 1.4.1

4-53

Configuring the IP Phones

The IP phones support out-of-band Dual-Tone Multifrequency (DTMF) mode 
according to RFC2833. In the Aastra Web UI, you can enable or disable this 
feature as required. The "out-of-band DTMF" is enabled by default.

In out-of-band mode, the DTMF audio is automatically clamped (muted) and 
DTMF digits are not sent in the RTP packets.

You can configure out-of-band DTMF on a global-basis using the configuration 
files or the Aastra Web UI.

A feature on the IP phone allows you to select the DTMF method that the phone 
uses to send DTMF digits from the IP phone via INFO messages. You can set the 
DTMF method as Real-Time Transport Protocol (RTP), SIP info, or both.

You can configure the DTMF method on a global or per-line basis using the 
configuration files or the Aastra Web UI.

In IP telephony, silence on a line (lack of voice) uses up bandwidth when sending 
voice over a packet-switched system. Silence suppression is encoding that starts 
and stops the times of silence in order to eliminate that wasted bandwidth.

Silence suppression is enabled by default on the IP phones. The phone negotiates 
whether or not to use silence suppression. Disabling this feature forces the phone 
to ignore any negotiated value.

You can configure this parameter via the configuration files or the Aastra Web UI.