in international phototelegraph communications, the occupation time of international telephone circuits often greatly exceeds the duration of the actual phototelegraph call
ITU-T F.107-1993 Referenced Document
ITU-T F.107 RULES FOR PHOTOTELEGRAPH CALLS ESTABLISHED OVER CIRCUITS NORMALLY USED FOR TELEPHONE TRAFFIC
ITU-T F.107-1993 history
1993ITU-T F.107-1993 RULES FOR PHOTOTELEGRAPH CALLS ESTABLISHED OVER CIRCUITS NORMALLY USED FOR TELEPHONE TRAFFIC
1988ITU-T F.107-1988 Rules for phototelegraph calls established over circuits normally used for telephone traffic