AWhen the social media team tweeted the photos shortly after 9 p.m. on Tuesday, no one could have guessed what impact this construction site would have on Wednesday:
“Ours is also at a depth of 5m #Glass fiber not safe from concrete drills, ”writes Telekom there. And: “Due to the considerable damage and the situation on the construction site, it will be extremely difficult to remedy the situation.” Deutsche Bahn. Not only the Lufthansa passengers stranded at Frankfurt Airport, who are affected by the IT malfunction, feel this on Wednesday, but also many Telekom customers, especially in the northern parts of Frankfurt.
“Step by step back on the grid”
Technicians worked through the night at the construction site to repair the damage, according to Telekom. The repair was made more difficult by the fact that concrete was also poured over the cables. A spokesman said in the morning that splicing work is starting. This means that the cable ends of the piecewise laid fiber optics are connected. “The affected mobile radio stations and customers are going back to the network step by step.”
As a rule, classic glass fiber underground cables are up to six kilometers long, containing four cables with twelve individual fibers each. A good 400 households can be connected to a fiber optic cable with 100 Mbit/s each. But of course only if it is not severed. The repair is expensive because of the many fibers: each fiber core is surrounded by a jacket, which in turn is surrounded by a protective layer that lies in a shell.
This shell measures 250 micrometers – about twice as wide as a human hair. To connect the fibers, the technicians need a so-called fusion splicing station. The welder measures the ends of the fibers to be joined and brings them together.
It is still completely unclear how it was possible that damage to a Deutsche Telekom fiber optic cable at a Deutsche Bahn construction site could lead to the entire IT of Deutsche Lufthansa being disrupted. As a rule, IT systems are set up redundantly. Data centers, of which there are many in Frankfurt due to the proximity to the De-Cix internet node, have diesel generators in addition to several independently switched power lines so that a connection can be restored at any time in the event of a large-scale failure. Of course, it’s different when the hardware is accidentally disconnected, as was the case with the fiber optic line. However, such a large-scale failure caused by a single construction site is unusual.