Rec. ITU-T Q.551 (01/1994) … TRANSMISSION CHARACTERISTICS OF DIGITAL EXCHANGES
FOREWORD
CONTENTS
1 Introduction
    1.1 General
    1.2 Definitions
2 Characteristics of interfaces
    2.1 Two-wire analogue interfaces
    2.2 Four-wire analogue interfaces
    2.3 Digital interfaces
3 Voice-frequency parameters of a connection between two interfaces of the same exchange
    3.1 General
    3.2 Transmission loss through the exchange
    3.3 Group delay
    3.4 Noise and total distortion
    3.5 Crosstalk
    3.6 Discrimination against out-of-band signals applied to the input interface
    3.7 Spurious out-of-band signals received at the output interface
    3.8 Echo and stability
4 Exchange transfer function - jitter and wander
Annex A … Information on the formulae used in this Recommendation to calculate weighted noise and signal-to-total distortion.
A.1 General
A.2 Weighted noise
A.3 Total distortion including quantizing distortion