ITU-T M.810-1988 Setting up and lining up an international voice-frequency telegraph link for public telegraph circuits (for 50, 100 and 200 baud modulation rates)
The designation of the control and sub-control stations should follow the principles given in Recommendations M.80 [1] and M.90 [2].By agreement between Administrations,one of the terminal international repeater stations will be designated as the voice-frequency telegraph link control station:the other terminal being the terminal sub-control station for the link.
ITU-T M.810-1988 history
1988ITU-T M.810-1988 Setting up and lining up an international voice-frequency telegraph link for public telegraph circuits (for 50, 100 and 200 baud modulation rates)