I worked on a project team implementing TR-Notruf 2.0¹ for a regional ISP. TR-Notruf is the technical specification for routing calls and signalling caller location information for emergency calls in Germany.

In that project I wrote the software that receives the call, matches the caller number to the customer record, encodes the customer location information in the metadata of the call, and (based on the location) routes the call to the local emergency services call center.

While the task was quite simple most of the complexity of the project was to make sure that this service was highly available since downtime could have a detrimental effect on the health of customers.

¹ https://www.bundesnetzagentur.de/DE/Fachthemen/Telekommunika...