Internet Stream Protocol
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The Internet Stream Protocol (ST) is an experimental protocol defined in Internet Engineering Note IEN-119 (1979), which was later revised in RFC 1190 (ST2) and RFC 1819 (ST2+). ST packets carried the experimental non-IP real-time stream protocol.
ST was envisioned to be the connection-oriented complement to IPv4, but it has never been introduced for public usage. Many of the concepts available in ST can be found today in MPLS.
In RFC 1819, ST2 distinguish its own packets with an Internet Protocol version number 5, despite it was never known as IPv5.
IP and ST packets can be distinguished by the IP Version Number field, i.e., the first four (4) bits of the packet; ST has been assigned the value 5 (see [RFC1700]). There is no requirement for compatibility between IP and ST packet headers beyond the first four bits. (IP uses value 4.)
For details, see fig. 10 in section 10.1 of that RFC. The ST2 header shows no similarity with IPv4 header. ST uses the same IP address structure and the same Link Layer protocol number (ethertype 0x800) as IP.
Note that, according to http://www.iana.org/assignments/protocol-numbers/, there is a "datagram mode" in which ST packets can be encapsulated over IP headers using protocol number 5.
[edit] See also
- IPv6 - Internet Protocol Version 6
