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TheInternet Stream Protocol (ST) is a family of experimental protocols first defined in Internet Experiment Note IEN-119 in 1979,[1] and later substantially revised in RFC 1190 (ST-II) and RFC 1819 (ST2+).[2][3][4]The protocol uses the version number 5 in the version field of theInternet Protocol header, but was never known as IPv5. The successor toIPv4 was thus namedIPv6 to eliminate any possible confusion about the actual protocol in use.
The Internet Stream Protocol family was never introduced for public use, but many of the concepts available in ST are similar to laterAsynchronous Transfer Mode protocols and can be found inMultiprotocol Label Switching (MPLS). They also presagedvoice over IP.
ST arose as the transport protocol of theNetwork Voice Protocol, a pioneering computer network protocol for transporting human speech over packetized communications networks, first implemented in December 1973 by Internet researcherDanny Cohen of theInformation Sciences Institute (ISI) as part ofARPA's Network Secure Communications (NSC) project.[5]
First specified in 1979, ST was envisioned as a connection-oriented complement toIPv4, operating on the same level, but using a different header format from that used for IP datagrams. According to IEN-119, its concepts were formulated by Danny Cohen, Estil Hoversten, and James W. Forgie. The protocol was notable for introducing the concepts ofpacketized voice (as used by voice over IP), atalkspurt (a continuous segment of speech between silent intervals), and specified delay and drop-rate requirements for packet services. It was implemented in theVoice Funnel.
Its second version, known variously as ST-II or ST2, was drafted by Claudio Topolcic and others in 1987 and specified in 1990.[3] It was implemented in theTerrestrial Wideband Network and its successor, theDefense Simulation Internet, where it was used extensively for distributed simulations and videoconferencing. This version later formed the core technology for transporting voice calls and other realtime streams within Canada'sIris Digital Communications System.
The final version of ST2, which was also known as ST2+, was drafted by the IETF ST2 Working group[6][7] and published in 1995 as RFC 1819.ST2 distinguishes its own packets with anInternet Protocol version number 5, although it was never known as IPv5.[4]
ST uses the same IP address structure and the samelink layer protocol number (ethertype 0x800) as IP.
Indatagram mode, ST packets could be encapsulated with IP headers usingprotocol number 5.[8]