It's the whole ecosystem with Erlang, OTP (Open Telecom Platform) and how they work with supervisors and monitors etc. Everything is built so that you can oper

It's the whole ecosystem with Erlang, OTP (Open Telecom Platform) and how they work with supervisors and monitors etc. Everything is built so that you can operate a telecom switch and never drop that emergency call. Erlang (Ericson language) is not necessary, you can also program for this in Elixir, although personally I prefer Erlang.