Today, you can make phone calls not only using landline telephony or cellphones. You can also use the Internet. Making voice (and video) calls via the Internet is possible due to the SIP, which stands for Session Initiation Protocol. This is the technology that consolidates various elements necessary for internet phone calls. A SIP proxy server operates as a receiver and a processor of incoming SIP data that travels from distant endpoints. As a result, the established connection transmits audio and video data.