DRE - Diameter Routing Engine
DSC- Diameter Signalling Control, DSC is a very common term which is widely used across Telecom Industries.
DRE is a customized version of DSC which telecom vendors like Diametriq named their product. Architecture wise both contains Diameter Routing Agent (DRA), Diameter Edge Agent (DEA), Subscription Locator Function (SLF) and a Diameter Interworking Function (IWF).
I hope you get some idea.