CC.2.7 Get Unified Procedure Step Information (N-GET)

This operation allows an SCU to get information from an SCP about a specific real-world Procedure Step which is represented as a Unified Procedure Step Instance. This operation shall be invoked by the SCU through the DIMSE N-GET Service.

CC.2.7.1 Unified Procedure Step IOD Subset Specification

The Application Entity which claims conformance to the UPS Pull or UPS Watch SOP Classes as an SCU may choose to retrieve a subset of the Attribute values maintained by the SCP. The Application Entity which claims conformance as an SCP to these SOP Classes shall support the attributes specified in Table CC.2.5-3.

CC.2.7.2 Service Class User Behavior

The SCU uses the N-GET to request the SCP to provide attributes and values of a Unified Procedure Step Instance. Since all UPSs are created as instances of the UPS Push SOP Class, the Affected SOP Class UID (0000,0002) in the N-GET request shall be the UID of the UPS Push SOP Class. See CC.3.1 for further details.

The SCU shall specify in the N-GET Service Element the UID of the SOP Instance from which attributes are to be retrieved.

The SCU shall specify the list of Unified Procedure Step Attributes for which values are to be returned. The SCU shall not specify Attributes which are defined within a Sequence, but rather specify the sequence itself to be retrieved in its entirety.

The SCU shall not request the value of the Transaction UID (0008,1195) attribute.

The SCU may request Attribute Values for optional Attributes which are not maintained by the SCP. In such a case, the SCU shall function properly regardless of whether the SCP returns values for those Attributes or not. This Service Class Specification places no requirements on what the SCU shall do as a result of receiving this information.

Note: In order to accurately interpret the character set used for the Attribute Values returned, it is recommended that the Attribute Value for the Specific Character Set (0008,0005) be requested in the N-GET request primitive.

The SCU shall be permitted to request and shall be capable of receiving values for any attribute as specified in Table CC.2.5-3. Additionally, values may be requested for optional attributes.

The SCU shall be capable of receiving all requested Attribute Values provided by the SCP in response to the N-GET indication primitive.

Note: If the SCU or the user will need access to the final state attributes it is the responsibility of the SCU to Subscribe (See CC.2.2) in order to receive State Change Events and then N-GET the necessary attributes promptly upon notification of a state change to COMPLETED or CANCELED. If the SCU sets the Deletion Lock when subscribing, a COMPLETED or CANCELLED instance will continue to persist on the SCP, using resources. It is important that the SCU remove the lock (e.g. by unsubscribing) after doing the N-GET on the COMPLETED or CANCELED instance.

CC.2.7.3 Service Class Provider Behavior

The SOP Class UID of the specified UPS instance will always be the UPS Push SOP Class UID, which might not match the UPS SOP Classes negotiated with the SCU. See CC.3.1 for further details.

The SCP shall return, via the N-GET response primitive, the selected Attribute values from the indicated Unified Procedure Step Instance to the SCU.

Note: The requirement for the SCP to respond to N-GET requests for UPS Instances which have moved to the COMPLETED or CANCELED state is limited. See CC.2.1.3 Service Class Provider Behavior.

The SCP shall not return the Transaction UID (0008,1195) attribute. This is necessary to preserve this attribute’s role as an access lock.

The SCP shall return, via the N-GET response primitive, the N-GET Response Status Code applicable to the associated request. A Failure Code shall indicate that the SCP has not retrieved the SOP Instance.

Bi-directional Authentication of machines/users/applications is possible at association time (see PS 3.7 and PS 3.15). PS 3.7 provides a “Refused: Not Authorized” error code. Further requiring or documenting authentication and/or authorization features from the SCU or SCP is beyond the scope of this SOP Class.

CC.2.7.4 Status Codes

The status values which are specific for this DIMSE operation are defined in Table CC.2.7-1. See PS 3.7 for additional response status codes.

Table CC.2.7-1

STATUS VALUES

Status Meaning Code
Warning Requested optional Attributes are not supported 0001
Failure Specified SOP Instance UID does not exist or is not a UPS Instance managed by this SCP C307