Advanced Network Settings41-001129-00 Rev 09, Release 1.4.1 4-53Configuring the IP PhonesConfiguring the IP PhonesOut-of-Band DTMFThe IP phones support out-of-band Dual-Tone Multifrequency (DTMF) modeaccording to RFC2833. In the Aastra Web UI, you can enable or disable thisfeature as required. The "out-of-band DTMF" is enabled by default.In out-of-band mode, the DTMF audio is automatically clamped (muted) andDTMF digits are not sent in the RTP packets.You can configure out-of-band DTMF on a global-basis using the configurationfiles or the Aastra Web UI.DTMF MethodA feature on the IP phone allows you to select the DTMF method that the phoneuses to send DTMF digits from the IP phone via INFO messages. You can set theDTMF 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 theconfiguration files or the Aastra Web UI.Silence SuppressionIn IP telephony, silence on a line (lack of voice) uses up bandwidth when sendingvoice over a packet-switched system. Silence suppression is encoding that startsand stops the times of silence in order to eliminate that wasted bandwidth.Silence suppression is enabled by default on the IP phones. The phone negotiateswhether or not to use silence suppression. Disabling this feature forces the phoneto ignore any negotiated value.You can configure this parameter via the configuration files or the Aastra Web UI.
