The CCITT, considering that to permit the sharing of responsibility for the maintenance of a high-standard of transmission between countries participating in the establishment of switched connections, it is necessary to specify limiting values of distortion at the international terminal exchanges; that on the other hand, to enable national switched networks to be interconnected, it is necessary to have a distribution plan of the telegraph distortion between national networks and the international junction circuits connecting up the international switching centres (international terminal switching centers).
ITU-T R.58 FRENCH-1988 history
1988ITU-T R.58 FRENCH-1988 STANDARD LIMITS OF TRANSMISSION QUALITY FOR THE GENTEX AND TELEX NETWORKS