Voice over Internet Protocol (VoIP) is the transmission of voice traffic over an IP-based network such as the Internet. The Session Initiation Protocol (SIP) is the signaling protocol widely used as a VoIP standard for creating and controlling communication sessions.
A VoIP-enabled device can make or receive calls using SIP by connecting to an Internet Telephony Service Provider (ITSP) such as Cloudli. VoIP calls to and from telephone numbers on the traditional Public Switched Telephone Network (PSTN) including Mobile numbers are possible by connecting through an ITSP.