The IRA is the further development of the IA No. 5.
T.50 : International Reference Alphabet (IRA) (Formerly International Alphabet No. 5 or IA5) – Information technology – 7-bit coded character set for information interchange (itu.int).
This recommendation specifies a 7-bit encoded character set with a number of options. It also includes guidance on how the options can be used to create specific national versions and application-oriented versions. It also specifies the International Reference Version (IRV) in which these options have been exercised.