A Voice over Internet Protocol
) is a protocol optimized for transmission of voice through the Internet or other packet switched network . VoIP is often used abstractly to refer to the actual transmission of voice (rather than the protocol implimenting it). VoIP is also known as IP Telephony
, Internet telephony
, Broadband telephony
, Broadband Phone
and Voice over Broadband
. "VoIP" is sometimes pronounced voyp .
Companies providing VoIP service are commonly referred to as providers, and Protocols which are used to carry voice signals over the IP network are commonly referred to as Voice over IP
protocols. They may be viewed as commercial realizations of the experimental Network Voice Protocol (1973) invented for the ARPANET providers. Some cost savings are due to utilizing a single network to carry voice and data, especially where users have existing underutilized network capacity that can carry VoIP at no additional cost. VoIP to VoIP phone calls are sometimes free, while VoIP to public switched telephone networks, PSTN , may have a cost that is borne by the VoIP user.
Voice over IP protocols carry telephony signals as digital audio, typically reduced in data rate using speech data compression techniques, encapsulated in a data packet stream over IP.
There are two types of PSTN to VoIP services: Direct Inward Dialing (DID) and access numbers
will connect the caller directly to the VoIP user while access numbers require the caller to input the extension number of the VoIP user.
Voice over IP has been a subject of interest almost since the first computer network. By 1973, voice was being transmitted over the early Internet. By Technology for transmitting voice conversations over the internet has been available to end users since at least the 1990''s. For instance, in 1996, a shrink-wrapped software product called Vocaltec .Internet Phone Release 4 provided VoIP, along with extra features such as voice mail and caller id However, it did not offer a gateway to the analog POTS system, so it was only possible to speak to other Vocaltec Internet Phone users.[ VocalTec is significant for their breakthroughs in real time voice compression which was vital at a time when the majority of users had at most a 28.8 kb/s dial up modem. In 1997, Level 3began development of its first softswith (a term they invented in 1998); softswitches were designed to replace a traditional hardware swithboards by serving as the gateway between two telephone networks.