27  DICOM Network Operations: SCU/SCP Requirements

27.1 Basic Concepts

┌─────────────────────────────────────────────────────────────────┐
│                    DICOM Network Model                          │
├─────────────────────────────────────────────────────────────────┤
│                                                                 │
│   SCU (Service Class User)         SCP (Service Class Provider) │
│   ─────────────────────────        ──────────────────────────── │
│   • The "Client" / Requester       • The "Server" / Responder   │
│   • Initiates the connection       • Listens on a port          │
│   • Sends the request              • Processes and responds     │
│                                                                 │
│        ┌─────────┐    Request     ┌─────────┐                   │
│        │   SCU   │ ─────────────► │   SCP   │                   │
│        │         │ ◄───────────── │         │                   │
│        └─────────┘    Response    └─────────┘                   │
│                                                                 │
└─────────────────────────────────────────────────────────────────┘

27.2 What SCU Needs to Know

To initiate a DICOM connection, the SCU must know:

Parameter	Description
SCP’s IP Address	Where to connect
SCP’s Port	Which port SCP is listening on
SCP’s AE Title	Identity of the target (Called AE)
Own AE Title	Identity of itself (Calling AE)

27.3 Comparison Table: DICOM Operations

Operation	Purpose	Direction of Data Flow	SCU Requires	SCP Requires
C-ECHO	Verify connectivity (“ping”)	SCU → SCP (just handshake)	SCP’s IP, Port, AE Title + Own AE Title	Own IP, Port, AE Title configured
C-FIND	Query/Search for studies	SCU → SCP (query), SCP → SCU (results)	SCP’s IP, Port, AE Title + Own AE Title	Own IP, Port, AE Title configured
C-STORE	Push images to destination	SCU → SCP (images)	SCP’s IP, Port, AE Title + Own AE Title	Own IP, Port, AE Title configured
C-GET	Pull images (same connection)	SCU → SCP (request), SCP → SCU (images on same assoc.)	SCP’s IP, Port, AE Title + Own AE Title	Own IP, Port, AE Title + SCU must also be C-STORE SCP
C-MOVE	Pull images (separate connection)	SCU → SCP (request), SCP → Move Dest (images)	SCP’s IP, Port, AE Title + Own AE Title + Move Dest AE	Own IP, Port, AE Title + Must know Move Dest’s IP, Port, AE

27.4 Visual Flow Diagrams

27.4.1 C-ECHO, C-FIND, C-STORE (Simple)

┌──────────────┐                      ┌──────────────┐
│     SCU      │                      │     SCP      │
│              │   1. Association     │              │
│  AE: SLICER  │ ──────────────────►  │ AE: ORTHANC  │
│              │   (to IP:Port)       │ localhost    │
│              │                      │ :4242        │
│              │   2. Request         │              │
│              │ ──────────────────►  │              │
│              │                      │              │
│              │   3. Response        │              │
│              │ ◄──────────────────  │              │
└──────────────┘                      └──────────────┘

SCU needs: SCP's IP (localhost), Port (4242), AE (ORTHANC)
         + its own AE (SLICER)

27.4.2 C-GET (Same Connection, Role Reversal)

┌──────────────┐                      ┌──────────────┐
│  SCU + SCP   │                      │  SCP + SCU   │
│   (C-GET)    │                      │   (C-GET)    │
│              │   1. Association     │              │
│  AE: SLICER  │ ──────────────────►  │ AE: ORTHANC  │
│              │                      │              │
│              │   2. C-GET Request   │              │
│              │ ──────────────────►  │              │
│              │                      │              │
│              │   3. C-STORE (imgs)  │              │
│   Must act   │ ◄──────────────────  │ Sends images │
│   as Store   │   (role reversal)    │ back as SCU  │
│     SCP      │                      │              │
└──────────────┘                      └──────────────┘

⚠️  SCU must ALSO support C-STORE SCP role on same association

27.4.3 C-MOVE (Separate Connection)

┌──────────────┐                      ┌──────────────┐
│     SCU      │   1. C-MOVE Req      │     SCP      │
│  AE: SLICER  │ ──────────────────►  │ AE: ORTHANC  │
│              │  "Send to SLICER"    │              │
└──────────────┘                      └──────┬───────┘
       ▲                                     │
       │                                     │ 2. SCP looks up
       │                                     │    SLICER's IP:Port
       │                                     ▼
       │                              ┌──────────────┐
       │   3. NEW Connection          │ PACS Config  │
       │      C-STORE images          │ DicomModali- │
       └──────────────────────────────│ ties table   │
                                      └──────────────┘

⚠️  SCP must have SCU's IP, Port, AE pre-configured!

27.5 Your Setup Example

┌─────────────────┐                    ┌─────────────────┐
│  Your App       │                    │  Orthanc        │
│  (e.g., DCMTK)  │                    │  (Local PACS)   │
│                 │                    │                 │
│  AE: DCMTK      │ ────────────────►  │  AE: ORTHANC    │
│  127.0.0.1      │                    │  localhost      │
│  :11112         │                    │  :4242          │
└─────────────────┘                    └─────────────────┘

For C-MOVE to work: Orthanc needs DCMTK's IP:Port configured
                    (already done in your configMacOS.json ✓)

27.6 Summary Table: Who Needs What

Parameter	SCU Must Know	SCP Must Know
Own AE Title	✅ Yes	✅ Yes
Own IP	❌ Not needed	✅ Yes (to bind/listen)
Own Port	❌ (ephemeral OK)	✅ Yes (to listen)
Remote AE Title	✅ Yes (Called AE)	⚠️ Only for C-MOVE dest
Remote IP	✅ Yes	⚠️ Only for C-MOVE dest
Remote Port	✅ Yes	⚠️ Only for C-MOVE dest

Key Insight: For C-MOVE, the SCP needs a “phone book” (DicomModalities in your config) to know where to send images. For C-GET, this isn’t needed since images flow back on the same connection.