IP telephony, also Internet telephony and Voice over Internet Protocol (short VOIP) is telephoning over the Internet using various Internet protocols. The network used for data transmission is also used for telephony. The transmission of the voice packets is prioritized so that there are no dropped calls (also Quality of Service, in short QoS called or end-to-end quality of service). The telephone devices used must be IP telephony-capable. Both classic desk phones (if necessary with an adapter) and softphones with headsets on PC, Mac and Linux can be used.