6.2 The DICOM Application Layer Structure
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## 6.2 The DICOM Application Layer Structure

A DICOM Application Entity and the Service Elements it includes are shown in Figure 6.2-1.

### Note

Annexes of this part define certain aspects of the DICOM Application Entity.

The heart of any DICOM Application Entity is specified by the following parts of the DICOM Standard:

- PS3.3, Information Object Definitions, which provides data models and Attributes used as a basis for defining SOP Instances that are operated upon by the services defined in this [art. Such SOP Instances are used to represent real-world occurrences of images, studies, patients, etc.

- PS3.4, Service Class Specifications, which defines the set of operations that can be performed on SOP Instances. Such operations may include the storage, retrieval of information, printing, etc.

- PS3.5, Data Structure and Encoding, which addresses the encoding of the Data Sets exchanged to accomplish the above services

- PS3.6, Data Dictionary, which contains the registry of DICOM Data Elements used to represent Attributes of SOP Classes

The DICOM Application Entity uses the Association and Presentation data services of the OSI Upper Layer Service defined in PS3.8. The Association Control Service Element (ACSE) augments the Presentation Layer Service with Association establishment and termination services. In the case of TCP/IP, the full equivalent of ACSE is provided by the DICOM Upper Layer Service. For the DICOM point-to-point stack, a minimum subset of ACSE is provided by the Session/Transport/Network Service.

The DICOM Application Entity uses the services provided by the DICOM Message Service Element. The DICOM Message Service Element specifies two sets of services.

- DIMSE-C supports operations associated with composite SOP Classes and provides effective compatibility with the previous versions of the DICOM Standard.

- DIMSE-N supports operations associated with normalized SOP Classes and provides an extended set of object-oriented operations and notifications. It is based on the OSI System Management Model and more specifically on the OSI Common Management Information Services (CMIS) Service definition.

Figure 6.2-1. DICOM Application Layer Structure

The DIMSE-C and DIMSE-N services are supported by a single DIMSE protocol that uses the DICOM-specific Message formatting and encoding.

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