DTMF does not work.You tried to check your voice mail using the DTMF pad, but the connection couldnot be established. There are three different protocols used for the transmission ofDTMF data, but only two of these are supported by Linphone (SIP INFO and RTPrfc2833). Check with your provider whether it supports one of these. The defaultprotocol used by Linphone is rfc2833, but if that fails you can set the protocol toSIP INFO in Preferences → Network → Other. If it does not work with either ofthem, DTMF transmission cannot be done using Linphone.8.7 GlossaryFind some brief explanation of the most important technical terms and protocols men-tioned in this document:VoIPVoIP stands for voice over Internet protocol. This technology allows the transmis-sion of ordinary telephone calls over the Internet using packet-linked routes. Thevoice information is sent in discrete packets like any other data transmitted overthe Internet via IP.SIPSIP stands for session initiation protocol. This protocol is used to establish mediasessions over networks. In a Linphone context, SIP is the magic that triggers thering at your counterpart's machine, starts the call, and also terminates it as soon asone of the partners decides to hang up. The actual transmission of voice data ishandled by RTP.RTPRTP stands for real-time transport protocol. It allows the transport of media streamsover networks and works over UDP. The data is transmitted by means of discretepackets that are numbered and carry a time stamp to allow correct sequencing andthe detection of lost packages.DTMFA DTMF encoder, like a regular telephone, uses pairs of tones to represent thevarious keys. Each key is associated with a unique combination of one high andone low tone. A decoder then translates these touch-tone combinations back intonumbers. Linphone supports DTMF signalling to trigger remote actions, such aschecking voice mail.164 KDE User Guide
