This hypothetical reference circuit is 5000 km long and applies to various types of carrier systems on coaxial cable and radio-relay systems, specially designed for very long international circuits. It has, for each direction of transmission, a total of: one pair of channel modulators which includes translation from the audio-frequency band to the basic group and vice versa; three pairs of group modulators, each pair including translation from the basic group to the basic supergroup and vice versa; six pairs of supergroup modulators, each pair including translation from the basic supergroup to a higher order modem and vice versa; twelve pairs of higher order modulators, each pair providing the necessary modulation stages to and from the line frequency.
ITU-T G.215 SPANISH-1993 Referenced Document
ITU-T G.123 Circuit Noise in National Networks - General Characteristics of International Telephone Connections and Circuits (Study Groups XII and XV) 6 pp
ITU-T G.212 HYPOTHETICAL REFERENCE CIRCUITS FOR ANALOGUE SYSTEMS GENERAL DEFINITIONS
ITU-T G.215 HYPOTHETICAL REFERENCE CIRCUIT OF 5000 KM FOR ANALOGUE SYSTEMS
ITU-T G.222 NOISE OBJECTIVES FOR DESIGN OF CARRIER-TRANSMISSION SYSTEMS OF 2500 km