Aastra Telecom SISIP 57I CT - Manual (Page 125)

Advanced Network Settings
41-001160-00, Rev 01 Release 2.0 4-59
Network Configuration of the IP Phones
Configuring the IP Phones Out-of-Band DTMF
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.
DTMF Method
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.
Silence Suppression
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.