How do travel agents check hotel availabilities?

I know that travel agents have various IATA systems (SABRE used to be one of them) for checking airline flight availability.

But how about hotels?
I mean if I tell my travel agent I want to stay in a one bedroom room in
City X between dates Y and Z, how does the travel agent find out what is available?

Is there something similar to the airline reservation system, only for hotels?
What is it called?