One-Way or Both-Way Operation of International Circuits - General Recommendations on Telephone Switching and Signalling - Functions and Information Flows for Services in the ISDN - Supplements (Study Group XI) 1 pp
In order to have as simple as possible equipment in international exchanges anc. to avoid Lmble seizures, System No. 4 has been designed in 1949-1954 for one-way operation of international circuits in semi-automatic and automatic working.