SIP – Session Initiation Protocol
SIP is a communications protocol used for signaling and controlling multimedia communication
sessions in applications of Internet telephony. This means that SIP is used to set up or tear down
calls. This protocol defines a specific list of messages that are exchanged in sequence in order to
establish communication between two SIP devices. Once those messages are exchanged, the
flow of a media stream will start. This media stream needs to be treated so it can be compressed
for a faster transmission and decompressed to be interpreted and reconstructed. This is a task
done by a codec. In this case, the same codec must be agreed by the source and the destination
of the stream, so both devices can understand it.