C.5.3 Association Negotiation for C-GET SOP Classes
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### C.5.3 Association Negotiation for C-GET SOP Classes

When an SCP performs the C-GET operation it induces a C-STORE operation for the purpose of transmitting composite SOP Instances for Storage. This induced C-STORE operation (called a sub-operation) requires a switch from the C-GET Presentation Context to a Presentation Context that supports the specific C-STORE sub-operation.

The following negotiation rules apply to retrieval based DICOM Query/Retrieve SOP Classes and Specialized DICOM Query/Retrieve SOP Classes that include the C-GET operation.

The Association-requester (retrieve SCU role) in the A-ASSOCIATE request shall convey:

1. C-GET operation support with:

   - one Abstract Syntax, in a Presentation Context, for each SOP Class supported

   - and optionally, one SOP Class Extended Negotiation Sub-Item, for each retrieval based SOP Class

2. Induced Storage sub-operation support where the SOP Class (in the retrieval SCU role) is acting as a Storage SOP Class in the SCP Role. See Figure C.5-1. For each supported Storage SOP Class, the A-ASSOCIATE request contains:

   - one Abstract Syntax in a Presentation Context

   - one SCP/SCU Role Selection Negotiation Sub-item with the SCP-role field set to indicate support of the SCP role. The SCP/SCU Role Selection Negotiation shall be used as defined in PS3.7.

Figure C.5-1. An Example of the Sub-Operation SCU/SCP Roles

### Note

This negotiation does not place any requirements on the SCU-flag of the SCP/SCU Role Selection Negotiation Sub-Item. It may be set if the Association-requester supports the Storage Service Class in the SCU role.

The Association-acceptor (retrieve SCP role) in the A-ASSOCIATE response shall convey:

1. C-GET operation support with:

   - one Abstract Syntax, in a Presentation Context, for each SOP Class supported

2. Induced Storage sub-operation support where the SOP Class (using the retrieval SCP role) is acting as a Storage SOP Class in the SCU Role. See Figure C.5-1. For each supported Storage SOP Class, the A-ASSOCIATE response contains both:

   - one Abstract Syntax, in a Presentation Context

   - one SCP/SCU Role Selection Negotiation Sub-item with the SCP-role field set to indicate the acceptance of the Association-requester's support of the SCP role. The SCP/SCU Role Selection Negotiation shall be used as defined in PS3.7.

### Note

The negotiation does not place any requirements on the SCU-flag of the SCP/SCU Role Selection Negotiation Sub-Item. It may be set if the Association-acceptor accepts the Storage SCP role. Figure C.5-2 illustrates an example of the retrieve (C-GET) negotiation.

Figure C.5-2 illustrates an example of the retrieve (C-GET) negotiation.

#### C.5.3.1 SOP Class Extended Negotiation

The SOP Class Extended Negotiation allows, at Association establishment, peer DICOM AEs to exchange application Association information defined by specific SOP Classes.

This is achieved by defining the Service-class-application-information field. The Service-class-application-information field is used to define support for relational-retrievals and alternative views for Enhanced Multi-Frame Image Conversion.

Figure C.5-2. An Example of the Retrieve (C-GET) Negotiation

Extended negotiation for SOP Classes based on the retrieval services that include C-GET operations is identical to the negotiation defined for C-MOVE, which is defined in Section C.5.2.1 of this Annex.

Extended negotiation for the SOP Classes of the Storage Service Class (for the C-STORE sub-operation) is defined in Annex B.

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