ITU-T RecommendationQ.552 – TRANSMISSION CHARACTERISTICS AT 2-WIRE ANALOGUE INTERFACES OF DIGITAL EXCHANGES
FOREWORD
CONTENTS
1 General
2 Characteristics of interfaces
    2.1 Characteristics of interface C2
        2.1.1 Exchange impedance
        2.1.2 Impedance unbalance about earth
        2.1.3 Longitudinal interference threshold level
        2.1.4 Relative levels
    2.2 Characteristics of interface Z
        2.2.1 Exchange impedance
        2.2.2 Impedance unbalance about earth
        2.2.3 Longitudinal interference threshold levels (under study)
        2.2.4 Relative levels
3 Characteristics of half-connections
    3.1 Characteristics common to all 2-wire analogue interfaces
        3.1.1 Transmission loss
        3.1.2 Group delay
        3.1.3 Single frequency noise
        3.1.4 Crosstalk
        3.1.5 Total distortion including quantizing distortion
        3.1.6 Discrimination against out-of-band signals applied to the input interface
        3.1.7 Spurious out-of-band signals received at the output interface
        3.1.8 Echo and stability
    3.2 Characteristics of interface C2
        3.2.1 Nominal value of transmission loss
        3.2.2 Noise
        3.2.3 Values of total distortion
    3.3 Characteristics of interface Z
        3.3.1 Nominal value of transmission loss
        3.3.2 Noise
        3.3.3 Values of total distortion
Annex A – Example of a longitudinal interference coupling network
Annex B – Example of a test method for measuring longitudinal interference threshold level
    B.1 Possible types of degradations
    B.2 Test circuits
    B.3 Test values