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