TRANSCODING ARRANGEMENT IN A SESSION INITIATION

This invention relates to a SIP and SDP protocols. The idea of the invention is to modify SDP descriptions included in SIP messages to facilitate transcoding. After receiving an INVITE message from a calling party, the SIP proxy negotiates with a transcoder for getting a list of codecs of the transcoder and their address information. The SIP proxy adds the codec list of the transcoder to the received SDP description in the invite message, and sends this way modified SDP description in an INVITE message to a called party. After receiving the modified SDP, the called party selects codecs or a list of suitable codecs according to preferences in the modified SDP and its own preferences.