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VoIP

Voice over IP

Voice over Internet Protocol (also voice over IP, VoIP or IP telephony) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).

Voice over IP has been implemented in various ways using both proprietary protocols and protocols based on open standards. These protocols can be used by a VoIP phone, special-purpose software, a mobile application or integrated into a web page. VoIP protocols include:

  • Session Initiation Protocol (SIP), connection management protocol developed by the IETF

  • H.323, one of the first VoIP call signaling and control protocols that found widespread implementation. Since the development of newer, less complex protocols such as MGCP and SIP, H.323 deployments are increasingly limited to carrying existing long-haul network traffic.[citation needed]

  • Media Gateway Control Protocol (MGCP), connection management for media gateways

  • H.248, control protocol for media gateways across a converged internetwork consisting of the traditional public switched telephone network (PSTN) and modern packet networks

  • Real-time Transport Protocol (RTP), transport protocol for real-time audio and video data

  • Real-time Transport Control Protocol (RTCP), sister protocol for RTP providing stream statistics and status information

  • Secure Real-time Transport Protocol (SRTP), encrypted version of RTP

  • Session Description Protocol (SDP), file format used principally by SIP to describe VoIP connections

  • Inter-Asterisk eXchange (IAX), protocol used between VoIP servers

  • Extensible Messaging and Presence Protocol (XMPP), instant messaging, presence information, and contact list maintenance

  • Jingle, adds peer-to-peer session control to XMPP

  • Skype protocol, proprietary Internet telephony protocol suite based on peer-to-peer architecture