Voice Over IP, or VoIP, is a channel for the delivery of voice communications and multimedia sessions over IP networks. Internet telephony provides communications services (voice, fax, SMS, voice-messaging) over the Internet, rather than via the public switched telephone network (PSTN). VoIP is a viable and cost-effective technology suited for businesses of all sizes.
Session Initiation Protocol, or SIP, is a communications protocol for initiating interactive user communication sessions. The most common applications of SIP are in Internet telephony for voice and video calls, as well as instant messaging all over IP networks. It makes it possible for users to initiate and receive communications from any location, and for networks to identify the users wherever they are.