There was a similar incident last Friday at 11:00 am in Düsseldorf, where during construction 17 fiber glass cables were cut at Königsallee. Backups did not work either (as it seems, that the rerouting went to the same line). Major outage for downtown Düsseldorf for 30 minutes (also affecting mobile and landlines) and during the rest of the day till early Saturday for some governement office and the judicial system and as far I was told also bank infrastructure.

It seems, redundancy is a bit weak by Telekom and it did not help that the competitors rely on Telekom infrastructure as well.

You can built a backup system, but you - unless you have your own network - rely at some point on third party infrastructure. And if they channel your backup throught the same place which was the reason for the fairlure you are out of luck at this very moment. Sure, you know better afterwards ...