On Wed, Dec 01, 2021 at 12:23:46PM +0100, Baldur Norddahl wrote: [ snip ]
And yes these are low bandwidth but on the other hand often stretch wifi to the very limits on the distance between bases. I am not claiming this is the same use case as a warehouse. I am pointing out that the argument that a system critical implementation _must_ be based on licensed frequencies does not hold as nothing could be more critical than a system that prevents trains from colliding.
The public transit market of rail industry has been in discussions for a while re: mitigation measures (such as licensed band) against possible interference on CBTC signalling data links. It is however a standardization issue (much like we here in internet infrastructure continue to discuss improvements to BGP and its lingering security issues, nothing is perfect in every industry I suppose..).
I do claim that the reason these metro train systems can boast of a very high uptime is not that it would be especially hard to jam their wifi based systems.
Moreover, the degree of disruption to loss of data on CBTC is further dependent upon individual deployment cases. One example is system falling back to ABS (non-moving block) operation during loss of confirmations on movement authorities, with trains continuing to run, albeit at reduced capacity. Anyhow it has not been a serious enough issue from operational and security standpoints to date to warrant immediate concern. It's a standardization matter. James