VoIP, short for voice over internet protocol, is a technology which uses the internet for the transmission of telephone calls. Voice data is sent in packets using IP over SIP. SIP trunks are lines used to make incoming and outgoing calls over an internet connection. SIP trunks enable an IP PBX to connect to the data network instead of to fixed line and voice traffic travels over the internet. SIP trunks can also be connected to existing PBX hardware using a converter.