7.2 DIMSE-Service-User Interaction
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## 7.2 DIMSE-Service-User Interaction

The DICOM Message Service Element receives notification and operation requests and their related information from the DIMSE-service-user. Two DICOM Application Entities take the roles as peer DIMSE-service-users in order to exchange notifications and operations.

A notification or operation is implemented as a request/response interaction carried out within the context of an established application Association. Typically, one DIMSE-service-user requests that a particular operation be performed (or notification be processed) and the other DIMSE-service-user attempts to perform the operation (or process the notification) and then reports the outcome of the attempt.

When engaging in the operations or notifications, the DIMSE-service-user takes on one of two roles:

1. it performs operations (on SOP Instances for which it has responsibility) that were invoked by a peer DIMSE-service-user. It may also emit change-of-state notifications for SOP Instances to one or more peer DIMSE-service-users. These notifications may be invoked as a result of operations initiated by other DIMSE-service-users.

2. it invokes the performance of an operation on a peer DIMSE-service-user. It may also receive notifications from a peer DIMSE-service-user.

These roles are depicted in Figure 7.2-1.

### Note

1. Role a) (called the Agent role in ISO terminology) is used by an implementation that conforms to a DICOM Service Class as an SCP.

2. Role b) (called the Manager role in ISO terminology) is used by an implementation that conforms to a DICOM Service Class as an SCU.

Figure 7.2-1. Operation and Notification Flow

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