Voice over Internet Protocol (VoIP)

Voice over Internet Protocol (VoIP) is a general term for a family of transmission technologies for delivery of voice communications over IP networks such as the Internet or other packet-switched networks. Other terms frequently encountered and synonymous with VoIP are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, and broadband phone.

VoIP systems usually interface with the traditional public switched telephone network (PSTN) to allow for transparent phone communications worldwide.[1]

VoIP systems employ session control protocols to control the set-up and tear-down of calls as well as audio codecs which encode speech allowing transmission over an IP network as digital audio via an audio stream. Codec use is varied between different implementations of VoIP (and often a range of codecs are used); some implementations rely on narrowband and compressed speech, while others support high fidelity stereo codecs.

History

* 1974 - The Institute of Electrical and Electronic Engineers (IEEE) published a paper entitled "A Protocol for Packet Network Interconnection."[2]
* 1981 - IPv4 is described in RFC-791.[3]
* 1985 - The National Science Foundation commissions the creation of NSFNET.[4]
* 1995 - VocalTec releases the first commercial Internet phone software.[5][6]
* 1996 -
o ITU-T begins the standardization of VoIP initially with the H.323 standard.[7]
o US telecommunication companies ask the US Congress to ban Internet phone technology.[8]
* 1997 - Level 3 began development of its first softswitch (a term they coined in 1998).[9]
* 1999 -
o The Session Initiation Protocol (SIP) specification RFC-2543 was released.[10]
o The first open source SIP PBX (Asterisk) is created by Mark Spencer of Digium.[11]
* 2004 - Commercial VoIP service providers proliferate.[12]