scope:

This specification applies to signalling schemes which make use of SSI but excluding Radio Electronic Tokenless Block systems .

Non-SSI schemes shall address the requirements of this standard, although the proposed architecture and operation may, by necessity be different.

All sections of this specification are mandatory with the exception of the desirable requirements listed in Section 4.

Purpose

The purpose of this specification is to define the requirements for "Signals On" Controls for use with Network Rail infrastructure equipped with Solid State Interlocking (SSI).