VoIP – Voice over Internet Protocol (also called IP telephony, internet telephony, and digital phone) is the routing of voice conversations over the Internet or any other IP-based network.
SIP – Session Initiation Protocol is a protocol developed by the IETF MMUSIC Working Group and proposed standard for initiating, modifying, and terminating an interactive user session that involves multimedia elements such as video, voice, instant messaging, online games, and virtual reality.
PSTN – Public Switched Telephone Network is the concentration of the world’s public circuit-switched telephone networks, in much the same way that the Internet is the concentration of the world’s public IP-based packet-switched networks.
ISDN – Integrated Services Digital Network is a type of circuit switched telephone network system, designed to allow digital (as opposed to analogue) transmission of voice and data over ordinary telephone copper wires, resulting in better quality and higher speeds, than available with analogue systems.
PBX – Private Branch eXchange (also called Private Business eXchange) is a telephone exchange that is owned by a private business, as opposed to one owned by a common carrier or by a telephone company.
IVR – In telephony, Interactive Voice Response is a computerised system that allows a person, typically a telephone caller, to select an option from a voice menu and otherwise interface with a computer system.
DID – Direct Inward Dialing (also called DDI in Europe) is a feature offered by telephone companies for use with their customers’ PBX system, whereby the telephone company (telco) allocates a range of numbers all connected to their customer’s PBX.
RFC – Request for Comments (plural Requests for Comments – RFCs) is one of a series of numbered Internet informational documents and standards very widely followed by both commercial software and freeware in the Internet and Unix communities.