The A-ASSOCIATE Service is invoked by a DIMSE-service-user to establish an Association with a peer DIMSE-service-user. Association establishment is always the first phase of DICOM Message Exchange.

The initiating DIMSE-service-user and the responding DIMSE-service-user shall include Application Association Information on the request and response primitive respectively. The meaning of this parameter is Application Context specific. For more information on the use of the Application Association Information, see Annex D.