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.

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. thumb|Cisco VoIP phone

History

• 1974 - The Institute of Electrical and Electronic Engineers (IEEE) published a paper entitled "A Protocol for Packet Network Interconnection."
• 1981 - IPv4 is described in RFC-791.
• 1985 - The National Science Foundation commissions the creation of NSFNET.
• 1995 - VocalTec releases the first commercial Internet phone software.
• 1996 -
• ITU-T begins the standardization of VoIP initially with the H.323 standard.
• US telecommunication companies ask the US Congress to ban Internet phone technology.
• 1997 - Level 3 began development of its first softswitch (a term they coined in 1998).
• 1999 -
• The Session Initiation Protocol (SIP) specification RFC-2543 was released.
• The first open source SIP PBX (Asterisk) is created by Mark Spencer of Digium.
• 2004 - Commercial VoIP service providers proliferate.
• 2009 - Skype releases a Wi-Fi only application for the iPhone

VoIP Implementations

Voice over IP has been implemented in various ways using both proprietary and open protocols and standards. Examples of available VoIP implementations include:

• SIP/RTP
• IMS
• H.323
• Skype

Further examples and comparisons are available from the following Wikipedia article: Comparison of VoIP software

Consumer market

Example of VoIP adapter setup in residential network A major development starting in 2004 has been the introduction of mass-market VoIP services over broadband Internet access services, in which subscribers make and receive calls as they would over the PSTN. Full phone service VoIP phone companies provide inbound and outbound calling with Direct Inbound Dialing. Many offer unlimited calling to the U.S., and some to Canada or selected countries in Europe or Asia as well, for a flat monthly fee as well as free calling between subscribers using the same provider. These services have a wide variety of features which can be more or less similar to traditional POTS.