https://www.3cx.es/voip-sip/voz-sobre-ip/
https://www.youtube.com/watch?v=8pLp2hLbP44
https://www.netelip.com/co/que-es-la-voz-ip-telefonia-ip/
https://vozip.com/
https://prezi.com/i8e_fnq7cfqq/voip-y-telefonia-sobre-ip/