Материал: part07

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5 Conventions​

The following conventions are used for the service description tables shown in this Part of the Standard.​

(=)​ The value of the parameter is equal to the value of the parameter in the column to the left.​

-​ Not applicable. The parameter shall not be present.​

C​ The parameter is conditional. The condition(s) are defined by the text that describes the parameter.​

M​ Mandatory usage​

MF​ Mandatory with a fixed value​

U​ The use of this parameter is a DIMSE Service User option​

UF​ User Option with a fixed value​

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6 Service Context​

ThissectiondefinestheDICOMMessageServiceElementandProtocolwithinthecontextoftheDICOMApplicationEntity.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 commu-​ nication 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, or​

•​theBasicDICOMFileService,whichprovidesaccesstoStorageMediaindependentlyfromspecificphysicalmediastorageformats​ and file structures.​

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.Forthisboundary,DICOMhasadoptedtheOSIStandards(PresentationServiceaugmentedbytheAssociationControl​ 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.​

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Medical Images and related information

DICOM Application Entity

Service Class Specifications

Information Objects Definitions

Dataset Structure and Encoding - Data Dictionary

Message Exchange

BOUNDARY:

DICOM Upper Layer Service

DICOM Upper Layer

Security Layer

(Optional)

TCP/IP Transport Layer

Network Exchange

On-Line Communication

Figure 6.1-1. DICOM Communication Model for Message Exchange​

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 ter-​ mination 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.​

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