F.4 Networking
Prev | F DICOM Conformance Statement Query-Retrieve-Server (Informative) | Next

## F.4 Networking

### F.4.1 Implementation Model

#### F.4.1.1 Application Data Flow

The division of EXAMPLE-QUERY-RETRIEVE-SERVER into the separate DICOM Application Entities represents a somewhat arbitrary partitioning of functionality. For the purpose of this document they are organized in this manner so as to detail their independent logical functionality.

By default all of the defined Application Entities have different AE Titles. However, EXAMPLE-QUERY-RETRIEVE-SERVER can be configured so that the QUERY-RETRIEVE-SCP AE and STORAGE-SCU AE share the same Application Entity Title. However, the QUERY-RETRIEVE-SCP AE and STORAGE-SCP AE must have separate Application Entity Titles.

Figure F.4.1-1. Example-Query-Retrieve-Server DICOM Data Flow Diagram

The Application Entities detailed in the Application Data Flow Diagram are all Windows NT applications.

- The STORAGE-SCU AE can send Composite SOP Instances. It handles requests from the QUERY-RETRIEVE-SCP AE to transmit Images to a specific DICOM destination. The STORAGE-SCU AE functions as a C-STORE SCU. (Note that in this example Conformance Statement this STORAGE-SCU AE does not allow a Local User to request that images be sent to a Remote AE. If a 'real' AE does allow this then this should be mentioned here and in the other appropriate areas of the Conformance Statement).

- The QUERY-RETRIEVE-SCP AE can handle incoming query and retrieve requests. It can handle external queries for Patient, Study, Series, and Image data, and also handle Image retrieval requests. The QUERY-RETRIEVE-SCP AE handles retrieval requests by issuing a command to the STORAGE-SCU AE to send the requested Images to the destination specified by the Remote AE. The QUERY-RETRIEVE-SCP AE functions as an SCP for C-FIND and C-MOVE requests.

- The STORAGE-SCP AE can receive incoming DICOM images and add them to the EXAMPLE-QUERY-RETRIEVE-SERVER database. It can respond to external Storage and Verification Requests as a Service Class Provider (SCP) for C-STORE and C-ECHO requests. The STORAGE-SCP AE can also handle Storage Commitment Push Model Requests. It can thus be used to query whether the EXAMPLE-QUERY-RETRIEVE-SERVER will confirm ownership and responsibility for specific Composite SOP Instances. The STORAGE-SCP AE currently only supports image type Composite SOP Instances.

#### F.4.1.2 Functional Definition of AEs

##### F.4.1.2.1 Functional Definition of STORAGE-SCU Application Entity

The STORAGE-SCU AE can be invoked by the QUERY-RETRIEVE-SCP AE to trigger the transfer of specific images to a remote destination AE. The STORAGE-SCU AE must be correctly configured with the host and port number of any external DICOM AEs that are to be C-MOVE retrieval destinations. The Presentation Contexts to use are determined from the headers of the DICOM files to be transferred. Some conversion of the DICOM image objects is possible if the original Presentation Context is not supported by the remote destination AE or if compression is preferred.

##### F.4.1.2.2 Functional Definition of QUERY-RETRIEVE-SCP Application Entity

The QUERY-RETRIEVE-SCP AE waits for another application to connect at the presentation address configured for its Application Entity Title. When another application connects, QUERY-RETRIEVE-SCP AE expects it to be a DICOM application. QUERY-RETRIEVE-SCP AE will accept Associations with Presentation Contexts for SOP Classes of the DICOM Query-Retrieve Service Class, and Verification Service Class. It will handle query and retrieve requests on these Presentation Contexts and respond with data objects with values corresponding to the contents of the EXAMPLE-QUERY-RETRIEVE-SERVER database. For C-MOVE requests the destination for the image objects is determined from the Destination AE Title contained in the C-MOVE request. When a retrieval request is received, the QUERY-RETRIEVE-SCP AE issues a command to the STORAGE-SCU AE to send the specified images to the C-MOVE Destination AE.

##### F.4.1.2.3 Functional Definition of STORAGE-SCP Application Entity

The STORAGE-SCP AE waits for another application to connect at the presentation address configured for its Application Entity Title. When another application connects, the STORAGE-SCP AE expects it to be a DICOM application. The STORAGE-SCP AE will accept Associations with Presentation Contexts for SOP Classes of the Verification, Storage, and Storage Commitment Service Classes. Any images received on such Presentation Contexts will be added to the EXAMPLE-QUERY-RETRIEVE-SERVER database. If a Storage Commitment Push Model N-ACTION Request is received then the STORAGE-COMMITMENT-SCP AE will immediately check if the referenced Composite SOP Instances are in the EXAMPLE-QUERY-RETRIEVE-SERVER database and return an N-EVENT-REPORT Notification. It will never 'cache' Storage Commitment Push Model Requests and wait for Composite SOP Instances to be received at a later time.

#### F.4.1.3 Sequencing of Real-World Activities

The only sequencing constraint that exists across all the EXAMPLE-QUERY-RETRIEVE-SERVER Application Entities is the fact that a Composite SOP Instance must be received by the STORAGE-SCP AE before Storage Commitment Push Model or Query-Retrieve Requests related to this SOP Instance can be successfully handled:

Figure F.4.1-2. Sequencing Constraints

Note that the only constraint is for the Composite SOP Instance to be received prior to the other events. For example, it is not necessary for the Storage Commitment Push Model Request to be received prior to receiving Query or Retrieval Requests related to the SOP Instance.

Prev | Up | Next
F.3.3 Additional Remarks for This Example | Home | F.4.2 AE Specifications