Service-Object-Pair (SOP) Classes and Service Class User/Service Class Provider are terms that define the DICOM Services and their role, either as client or server.DICOM is based on two-way communication, which means that there is always one device that sends and one that receives. Or in DICOM terminology, one device that invokes an operation and the other one that performs it. In DICOM these roles are called Service Class User (SCU) and Service Class Provider (SCP). Matching roles, therefore, match SCUs with SCPs.
A DICOM device can have the role of a SCU or SCP, much like any two people engaged in conversation; both can be speakers and listeners. A device can act in different roles. Service class provider (SCP) defines the role of a device when it functions as a server (i.e. when it is set up to receive images).
Devices may be Service Class Provider (SCP) only, like a workstation in a physician’s home that only receives images. Or they may have both User and Provider roles, such as an archive that can send as well as receive images. The User (SCU) typically initiates the communication, or sets up the Association.A printer is an obvious example of an SCP of the Print SOP class, which has to match a print spooler, workstation, or modalities that support the Print SOP class as an SCU.