Voice over Internet Protocol,
also called VoIP, IP Telephony, Internet telephony, Broadband
telephony, Broadband Phone and Voice over Broadband is the routing
of voice conversations over the Internet or through
any other IP-based network.
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 or VoIP 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 - see attached image - 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's borne by the VoIP user.
There are two types of PSTN to VoIP services: -Direct Inward Dialing (DID) and access numbers.
DID will connect the caller directly to the VoIP user while access
numbers require the caller to input the extension number of the VoIP user.