scope:

This SIN applies to all Critical Signalling Services, that are carried over both the FTN and FTNx telecoms networks and require separate telecoms links that provide diversity for the signalling system.

This includes, but is not limited to, the following types of Signalling Systems:

a) Solid State Interlockings (SSI)

b) Time Division Multiplexor (TDM) Route Relay Interlocking (RRI)

c) Modern equivalents of SSI, Zone Controller, Atkins Electrologix, modular signalling

In the document these are collectively known as critical signalling systems

Lineside equipment is excluded from the scope of this SIN as are all Train Describer (TD) connections.

Purpose

The purpose of this SIN is for Network Rail Telecom (NRT) to carry out a national audit of all Critical Signalling Services that are carried on both the Fixed Telecoms Network (FTN) and Fixed Telecoms Network Expansion (FTNx) telecoms network and to correlate that there are no single points of failure that could affect the performance and operation of the Signalling System.

The correlation will confirm that:

a) route and Regions have assurance that Critical Signalling Systems, that require diversity on the telecoms network, do so, and can be relied upon.

b) any relevant standard and design rules, from a telecoms network provision perspective have been followed.

c) the Critical Signalling Services, have the correct service status, within NRT's Inventory System

d) the Critical Signalling Services are shown to be routed over the networks, as per the signed off design, and implemented on the relevant management platform, including that the correct method of trail protection has been applied and configured.