CONTENTS

 1     Introduction
 2     Line signals
        2.1     Carrier frequency
        2.2     Transmitted spectrum
        2.3     Modulation rate
        2.4     Coding
 3     Interchange circuits
        3.1     List of interchange circuits
        3.2     Transmit data
        3.3     Receive data
        3.4     Timing arrangements
        3.5     Data rate control
        3.6     Circuit 106
        3.7     Circuit 109
        3.8     Electrical characteristics of interchange circuits
        3.9     Fault condition on interchange circuits
 4     Scrambler and descrambler
        4.1     Scrambler/descrambler allocation
 5     Operating procedures
        5.1     Recommendation V.25 automatic answering sequence
        5.2     Receiver conditioning signal
        5.3     Rate signal
        5.4     Start-up procedure
        5.5     Retrain procedure
 6     Testing facilities
 7     Asynchronous to synchronous conversion protocol – Modes of operation
        7.1     Transmitter
        7.2     Receiver
Annex A
        A.1     Definitions of Terms Used
        A.2     Interworking of Duplex Modems
Appendix I – Interworking procedure for echo cancelling modems
        I.1     Interworking of echo cancelling modems