scope:

General

The requirements contained in this specification apply both to new TDM systems and retrofit replacements. However extensions or part replacements may not be required to meet every requirement within this specification if it can be demonstrated that this is necessary to achieve compatibility with existing connected equipment.

The TDM system described in this specification is considered suitable for signalling applications where the transmission of data must be achieved to a safety integrity level (SIL) equivalent to 1. Example applications include:

• Remote interlockings;

• CCTV level crossing control;

• Emergency alarms between signalling control centres;

• Condition monitoring.

The above applications govern the interface requirements of the TDM system and also the performance requirements demanded by the different signalling applications

Purpose

Aim

The aim of this specification is to define the requirements for a basic bit to bit Time Division Multiplex (TDM) transmission system suitable for use in a variety of signalling applications on Network Rail.

Bit to bit describes a one to one relationship between the input at one end and the output at the other. This may include multi-drop applications. It specifically excludes any bit manipulation such as panel processing or button processing.

Multi-drop applications are only applicable to dedicated networks where the link can be considered point-to-point.

The requirements address the needs of modern signalling schemes, whether for new works or as part of a renewal, and thus reduce the level of prescriptive detail in tenders regarding the TDM system.