9.3.5 C-ECHO Protocol
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### 9.3.5 C-ECHO Protocol

The information necessary for the C-ECHO request and indication DIMSE-C primitives are conveyed in the C-ECHO-RQ Message. The information necessary for the C-ECHO response and confirmation DIMSE-C primitives are conveyed in the C-ECHO-RSP Message.

#### 9.3.5.1 C-ECHO-RQ

The C-ECHO-RQ Message contains fields as defined in Table 9.3-12 Each field shall conform to DICOM encoding and Value Representation as defined in PS3.5. Fields are required as specified in the C-ECHO service definition unless otherwise noted in Table 9.3-12. Fields not specified in the C-ECHO service definition but present in Table 9.3-13 are required by the DIMSE-C protocol.

Table 9.3-12. C-ECHO-RQ Message Fields

Message Field | Tag | VR | VM | Description of Field
--- | --- | --- | --- | ---
Command Group Length | (0000,0000) | UL | 1 | The even number of bytes from the end of the value field to the beginning of the next group.
Affected SOP Class UID | (0000,0002) | UI | 1 | SOP Class UID associated with this operation.
Command Field | (0000,0100) | US | 1 | This field distinguishes the DIMSE‑C operation conveyed by this Message. The value of this field shall be set to 0030H for the C-ECHO-RQ Message.
Message ID | (0000,0110) | US | 1 | Implementation-specific value that distinguishes this Message from other Messages.
Command Data Set Type | (0000,0800) | US | 1 | This field indicates that no Data Set is present in the Message and shall be set to a value of 0101H.

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