The Internet community uses IPv4 and has used IPv6 for a couple of years. IANA is the organization that has the worldwide responsibility of assigning numbers to everything related to the Internet, which includes versions of the IP protocol. IANA assigned version 6 to the IPng protocol in 1995 following a request by the IPng working group.
What about "IP version 5"? IPv5 is an experimental resource reservation protocol intended to provide quality
of service (QoS), defined as the Internet Stream Protocol (ST). It can provide real-time transport of multimedia such as voice, video, and real-time data traffic across the Internet. This protocol is based on previous work of Jim Forgie in 1979, as documented in IETF Internet Experiment Note 199. It consists of two protocols—ST for the data transport and Stream Control Message Protocol (SCMP). IPv5, also called ST2, is documented in RFC 1819 and RFC 1190.
Internet Streaming Protocol version 2 (ST2) is not a replacement for IPv4. It is designed to run and coexist with IPv4. The number 5 was assigned by IANA because this protocol works at the same link-layer framing as IPv4. A typical distributed multimedia application can use both protocols: IP for the transfer of traditional data and control information such as TCP/UDP packets, and ST2 for real-time data carriers. ST2 uses the same addressing schemes as IPv4 to identify hosts. Resource reservation over IP is now done using other protocols such as Resource Reservation Protocol (RSVP).