CONTENTS

 1     Introduction
        1.1     General
        1.2     Definitions
                  1.2.1     Exchange test points, exchange input and output and half-connections
                  1.2.3     Measurement conditions
                  1.2.4     Transmission loss
                  1.2.6     Digital parameters
 2     Characteristics of interfaces
        2.1     Two-wire analogue interfaces
                  2.1.1     Interface Z
                  2.1.2     Interface C₂
        2.2     Four-wire analogue interfaces
                  2.2.1     Interface C₁
        2.3     Digital interfaces
                  2.3.1     Interface A
                  2.3.2     Interface B
                  2.3.3     V-type 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
                  3.3.1     Absolute group delay
                  3.3.2     Group delay distortion
        3.4     Noise and total distortion
                  3.4.1     Weighted noise
                  3.4.2     Total distortion including quantizing 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 ratio
        A.1     General
        A.2     Weighted noise
                  A.2.1     Weighted noise for an input connection originating from a Z-interface
                  A.2.2     Weighted noise for an output connection terminating in a Z-interface
                  A.2.3     Weighted noise for a whole connection originating from and terminating in a Z‑interface
                  A.2.4     Weighted noise for an input connection originating from a 2-wire or 4-wire C‑interface with or without signalling on the speech wires
                  A.2.5     Weighted noise for an output connection terminating at a 2-wire C-interface with L_o ³ or a 4‑wire C-interface both with or without signalling on the speech wires
                  A.2.6     Weighted noise for an output connection terminating at a 2-wire C-interface with L_o <-5 dBr and with or without signalling on the speech wires
                  A.2.7     Weighted noise for a whole connection originating from and terminating in 2-wire or 4‑wire C‑interfaces with or without signalling on the speech wires     24
        A.3     Total distortion including quantizing distortion
                  A.3.1     Total distortion including quantizing distortion for an input connection originating from a Z-interface
                  A.3.2     Total distortion including quantizing distortion for an output connection terminating in a Z‑interface
                  A.3.3     Total distortion including quantizing distortion for a whole connection originating from and terminating in a Z-interface
                  A.3.4     Total distortion including quantizing distortion for an input connection originating from a 2-wire or a 4‑wire C-interface
                  A.3.5     Total distortion including quantizing distortion for an output connection terminating in a 2‑wire or a 4‑wire C-interface
                  A.3.6     Total distortion including quantizing distortion for a whole connection originating from and terminating in 2-wire or 4-wire C-interfaces
Annex B – Explanation of power, dBm, dBr, dbm0 and mW units of speech band signals in ITU
        B.1     Introduction
        B.2     The case of resistive nominal impedances, constant with frequency
        B.3     The case of complex nominal impedances, varying with frequency