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 PS 3.5. 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 which 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.

9.3.5.2 C-ECHO-RSP

The C-ECHO-RSP Message contains fields as defined in Table 9.3-13 and in Annex C. Each field shall conform to DICOM encoding and Value Representation as defined in PS 3.5. Fields are required as specified in the C-ECHO service definition unless otherwise noted in Table 9.3-13. Fields not specified in the C-ECHO service definition but present in Table 9.3-13 are required by the DIMSE-C protocol.

Table 9.3-13 C-ECHO-RSP 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 the 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 8030H for the C-ECHO-RSP Message.
Message ID Being Responded To (0000,0120) US 1 Shall be set to the value of the Message ID (0000,0110) field used in associated C-ECHO-RQ Message.
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.
Status (0000,0900) US 1 Indicates the status of the response. It shall have a value of Success.

9.3.5.3 C-ECHO protocol procedures

The C-ECHO procedures are initiated by the invoking DIMSE-service-user issuing a C-ECHO request primitive. On receipt of the C-ECHO request primitive the DIMSE-C protocol machine shall:

⎯ construct a Message conveying the C-ECHO-RQ

⎯ send the Message using the P-DATA request service (See 8.1)

On receipt of a Message conveying a C-ECHO-RQ the DIMSE-C protocol machine shall issue a C-ECHO indication primitive to the performing DIMSE-service-user.

On receipt of a C-ECHO response primitive, issued by the performing DIMSE-service-user, the DIMSE-C protocol machine shall:

⎯ construct a Message conveying the C-ECHO-RSP

⎯ send the Message using the P-DATA request service (See 8.1)

On receipt of a Message conveying a C-ECHO-RSP the DIMSE protocol machine shall issue a C-ECHO confirmation primitive to the invoking DIMSE-service-user, thus completing the C-ECHO procedure.