Why does telecom use 48V rectifier?

Why does telecom use 48V?

Back in the day, when Telephony equipment was being developed, 48 was the chosen system voltage because it's considered safe “low voltage”, and reduced amperage requirement of equipment powered at this voltage.

Why does telecom power use the 48V rectifier?

The 48V rectifier provided by Ugamat is also Safer and more Reliable.