DICOM PS3.7 2021d - Message Exchange

6 Service Context (Current)
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# 6 Service Context

This section defines the DICOM Message Service Element and Protocol within the context of the DICOM Application Entity. Specifically, this section provides a model to clarify a number of concepts for digital imaging and communications and introduces key terms used throughout the Standard. This model has been used to partition the Application Layer of the DICOM Standard into separate parts.

## 6.1 DICOM Communication Model for Message Exchange

Figure 5-1 in PS3.1 presents the general communication model of the DICOM Standard, which spans both network (on-line) and storage media interchange (off-line) communications. Application Entities may utilize any of the following transport mechanisms:

- the DICOM Message Service and Upper Layer Service, which provides independence from specific physical networking communication support and protocols such as TCP/IP,

- the DICOM Web Service API and HTTP Service, which allows use of common hypertext and associated protocols for transport of DICOM services,

- the Basic DICOM File Service, which provides access to Storage Media independently from specific physical media storage formats and file structures, or

- DICOM Real-Time Communication, which provides real-time transport of DICOM metadata based on SMPTE and RTP.

PS3.7 focuses on the DICOM Message Service and here the OSI Basic Reference Model is used to model the interconnection of medical imaging equipment. As shown in Figure 6.1-1 several layers of communication protocols are distinguished. DICOM uses the OSI Upper Layer Service to separate the exchange of DICOM Messages at the Application Layer from the communication support provided by the lower layers.

This OSI Upper Layer Service boundary allows peer Application Entities to establish Associations, transfer Messages and terminate Associations. For this boundary, DICOM has adopted the OSI Standards (Presentation Service augmented by the Association Control Service Element). It is a simple service that isolates the DICOM Application Layer from the specific stack of protocols used in the communication support layers.

The DICOM Upper Layer protocol augments TCP/IP. It combines the OSI upper layer protocols into a simple-to-implement single protocol while providing the same services and functions offered by the OSI stack.

The DICOM Upper Layer Service is defined in PS3.8.

Figure 6.1-1. DICOM Communication Model for Message Exchange

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DICOM PS3.7 2021d - Message Exchange