VoIP requires protocols for various components to work smoothly in its communications services. Virtually every device in the world uses a standard called Real-Time Protocol (RTP) for transmitting audio and video packets between communicating computers. The Internet Engineering Task Force (IETF) defines RTP in RFC 3550. The payload format for a number of CODECs is defined in RFC 3551, although the International Telecommunications Union ITU and other IETF RFCs define other payload format specifications.

RTP addresses issues like packet order, and it provides mechanisms to help address delay and jitter. These mechanisms include the Real-Time Control Protocol, or RTCP, which also is defined in RFC 3550. In addition, one of the main areas of concern about Internet communications is the eavesdropping potential. To address security concerns, Secure RTP was created (defined in RFC 3711), and this technology provides for encryption, authentication, and integrity of the audio and video packets that are transmitted between communicating devices.

But, before audio or video media can be transmitted between two computers, various protocols must be employed to find the remote device and to negotiate a communications transmission. The protocols that are essential to this process are known as “call-signaling protocols,” the most popular of which are H.323 and SIP; but there are many other protocols that help users to perform various tasks and these protocols need devices in order to function properly. The following protocols are most common to the majority of the devices utilized today.

Types of VoIP Protocols

  • H.323
    In 1995, researchers wanted to solve the problem of how two computers could initiate communication in order to exchange audio and video media streams. H.323 and SIP (Session Initiation Protocol)...
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  • Megaco H.248
    H.323, used for Local Area Networks (LANs), isn't capable of scaling to larger public networks. Enter Megaco, the result of a joint effort between the Internet Engineering Task Force (IETF)...
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  • MGCP
    MGCP (Media Gateway Control Protocol) is an internal protocol used within a Voice over IP (VoIP) system, and specified in RFC 3435. This simple protocol was developed primarily to address...
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  • MIME
    MIME, or Multipurpose Internet Mail Extensions, refers to an official Internet standard that defines how messages must be formatted so that they can be exchanged among various email systems. The...
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  • RVP
    Remove Voice Protocol (RVP or RVP/IP) is a proprietary specification developed by MCK Communications for transporting digital telephony sessions over packet- or circuit-based data networks. The protocol is used primarily...
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  • SAP
    Session Announcement Protocol (SAP) is an announcement protocol that is used by session directory clients to assist the advertisement of multicast multimedia conferences and other multicast sessions. It also is...
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  • SDP
    SDP is an IETF standard that allows a multimedia device to describe the kinds of media that has to offer or that it wishes to accept. As part of this...
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  • SGCP
    Christian Huitema and Mauricio Arango published the Simple Gateway Control Protocol (SGCP) in 1998 by as part of the development of the "Call Agent Architecture" at Telcordia. In this architecture,...
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  • SIP
    SIP is an application-layer control protocol that allows users to create, modify, and terminate sessions with one or more participants. It can be used to create two-party, multiparty, or multicast...
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  • Skinny (SCCP)
    The use of the word, "skinny," often refers to a scaled down device that functions purposefully with fewer features or functions than its "fat" version of that same device. In...
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