ITU-T O.6 PDF

Introduction

The intent of this Recommendation is to specify a single nominal reference frequency of 1020 Hz in order to provide guidance to manufacturers and Administrations in the design and operation of new equipment and systems. This Recommendation is not intended to have an effect on existing equipment or systems except where modifications are required to allow for interworking. For instance, an older analogue exchange would need to be provided with new reference frequency capability if circuits were provided between it and digital exchanges.