The present document specifies the standards allowed to implement layer 1 on the NG interface. The specification of transmission delay requirements and O&M requirements are not in the scope of the present document. In the following, 'layer 1' and 'physical layer' are assumed to be synonymous.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.

The main functions of layer 1 are summarized in the following:

• Interface to physical medium;
• Frame delineation;
• Line clock extraction capability;
• Layer 1 alarms extraction and generation;
• Transmission quality control.

The support of any suitable layer 1 technique - like point-to-point or point-to-multipoint techniques - shall not be prevented.

The description of the interface towards the management plane is out of scope of this document, but at least the following O&M functions should be foreseen:

• Performance monitoring functions;
• Alarm status reporting functions;
• Synchronisation source management.