ITU-T S.18-1989 Conversion between International Telegraph Alphabet No. 2 and International Alphabet No. 5 - Telegraph Services Terminal Equipment (Study Group IX) 6 pp
that the Recommendation cited in [i] defines International Telegraph Alphabet No. 2 (ITA2), which is used, for example, in the international telex service;
ITU-T S.18-1989 history
1989ITU-T S.18-1989 Conversion between International Telegraph Alphabet No. 2 and International Alphabet No. 5 - Telegraph Services Terminal Equipment (Study Group IX) 6 pp