Classical Central Instance or Standalone Enqueue
There are two kinds of enqueue services in SAP system.
1) Classical Central Instance with the Message Server and Enqueue service running in a dialog instance. Usually a ENQ work process is also available;
2) Standlaone Enqueue Server (ENSA) where the Message Server and enqueue runs in a separated application server called ASCSXX or SCSXX where XX is the instnace number
In order to check if your system runs a Classical CI or a Standalone Enqueue you can check in SM12 -> Extras -> Diagnosis
Standalone Enqueue Server: