ITU-T J.15-1989 Lining-up and Monitoring an International Sound-Programme Connection - Line Transmission of Non-Telephone Signals - Transmission of Sound-Programme and Television Signals (Study Group XV) 4 pp
The use of level definitions is given in CCIR Recommendation 574.
ITU-T J.15-1989 history
1989ITU-T J.15-1989 Lining-up and Monitoring an International Sound-Programme Connection - Line Transmission of Non-Telephone Signals - Transmission of Sound-Programme and Television Signals (Study Group XV) 4 pp