Central lights permanently.

[Bjoern]

Yes, it works perfect in the past. It shows if anyone call at the company's main number. The main number is not only linked to a specific telephone, but to several telephones in a large office. If you call this number all phones will ring at the same time. But every phone has his same number too. This has therefore been resolved so that no one can call from external to only on specific phone number. External callers forward by Placetel to the central office number. Only internal can call the individual devices.
I think the goal should be that one sees here if someone calls on the central office. I think in case someone is in conversation and a call comes from outside.