Great Western Coffee Shop

Not sure if I should make a new topic to ask this, but it might be relevant here.

A colleague at my recently completed 1-year work placement once told me that railway systems were SIL-4. (Saftey Integrity Level). I'm not sure if he was refering to central door locking on board trains, or to signaling, or to both.

Does anyone know what he meant, and if SILs, defined in IEC-61508 (which I haven't read and don't know much about), even apply to railways?

Original was posted within http://www.firstgreatwestern.info/coffeeshop/index.php?topic=12771.0

It was relevant where it was posted, Rhydgaled ... however, that topic has sailed back into stormy waters and has been locked (again!) and I wanted to leave your question open and answerable in calmer seas.

Railway fixed infrastructure systems require a high level of system security, both in the sense of reliably and intrusion prevention (hacking)

The obvious system is signalling however there are others such as SCADA for electrification. There are a number of comms systems used from dedicated copper wires, dedicated fibre to multiplexed copper and fibre, GSM-R and in some locations connections onto the BT network,  I cannot go into the specifics of how the systems are routed, usually modern critical systems have 2 diverse routes to a location where such comms are required with elaborate power supply systems.

The levels of encryption are the similar to those used by MoD, the nuclear industry etc.