Editing Voice over IP (section)

==Protocols==
Voice over IP has been implemented with [[proprietary protocol]]s and protocols based on [[Open standard#Protocols|open standards]] in applications such as VoIP phones, mobile applications, and [[Web-based VoIP|web-based communications]].

A variety of functions are needed to implement VoIP communication. Some protocols perform multiple functions, while others perform only a few and must be used in concert. These functions include:
* ''Network'' and ''transport'' – Creating reliable transmission over unreliable protocols, which may involve acknowledging receipt of data and retransmitting data that wasn't received.
* ''Session management'' – Creating and managing a [[Session (computer science)|session]] (sometimes glossed as simply a "call"), which is a connection between two or more peers that provides a context for further communication.
* ''[[Signaling (telecommunications)|Signaling]]'' – Performing registration (advertising one's presence and contact information) and discovery (locating someone and obtaining their contact information), dialing (including reporting [[Call-progress tone|call progress]]), negotiating capabilities, and call control (such as hold, mute, transfer/forwarding, dialing DTMF keys during a call [e.g. to interact with an [[automated attendant]] or [[IVR]]], etc.).
* ''Media description'' – Determining what type of media to send (audio, video, etc.), how to encode/decode it, and how to send/receive it (IP addresses, ports, etc.).
* ''Media'' – Transferring the actual media in the call, such as audio, video, text messages, files, etc.
* ''Quality of service'' – Providing out-of-band content or feedback about the media such as [[Lip sync|synchronization]], statistics, etc.
* ''Security'' – Implementing access control, verifying the identity of other participants (computers or people), and encrypting data to protect the privacy and integrity of the media contents and/or the control messages.

VoIP protocols include:
* [[Matrix (protocol)|Matrix]], open standard for [[online chat]], voice over IP, and [[videotelephony]]
* [[Session Initiation Protocol]] (SIP),<ref>{{Cite journal|last1=Montazerolghaem|first1=Ahmadreza|last2=Moghaddam|first2=Mohammad Hossein Yaghmaee|last3=Leon-Garcia|first3=Alberto|date=March 2018|title=OpenSIP: Toward Software-Defined SIP Networking|url=https://ieeexplore.ieee.org/document/8012472|journal=IEEE Transactions on Network and Service Management|volume=15|issue=1|pages=184–199|doi=10.1109/TNSM.2017.2741258|issn=1932-4537|arxiv=1709.01320|s2cid=3873601}}</ref> connection management protocol developed by the IETF
* [[H.323]], one of the first VoIP call signaling and control protocols that found widespread implementation.<ref>{{cite web |url=https://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a0080092947.shtml |title=H.323 and SIP Integration |access-date=January 24, 2020}}</ref> 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.<ref>{{Cite web|last=Omar |first=Ahmed |title=Voice OVER IP (VOIP) |url=https://www.academia.edu/39621401}}</ref>
* [[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 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), a syntax for session initiation and announcement for multi-media communications and [[WebSocket]] transports.
* [[Inter-Asterisk eXchange]] (IAX), protocol used between [[Asterisk PBX]] instances
* [[Extensible Messaging and Presence Protocol]] (XMPP), instant messaging, presence information, and contact list maintenance
* [[Jingle (protocol)|Jingle]], for peer-to-peer session control in XMPP
* [[Skype protocol]], proprietary Internet telephony protocol suite based on peer-to-peer architecture