The components of this parameter are defined in Table 170.

Table 170– RequestHeader






Common parameters for all requests submitted on a Session.




The secret Sessionidentifier used to verify that the request is associated with the Session. The SessionAuthenticationTokentype is defined in 7.31.



The time the Clientsent the request. The parameter is only used for diagnostic and logging purposes in the server.



A requestHandleassociated with the request. This Clientdefined handle can be used to cancel the request. It is also returned in the response.



A bit mask that identifies the types of vendor-specific diagnostics to be returned in diagnosticInfo response parameters.

The value of this parameter may consist of zero, one or more of the following values. No value indicates that diagnostics are not to be returned.

Bit Value Diagnostics to return

0x0000 0001ServiceLevel / SymbolicId

0x0000 0002ServiceLevel / LocalizedText

0x0000 0004ServiceLevel / AdditionalInfo

0x0000 0008ServiceLevel / Inner StatusCode

0x0000 0010ServiceLevel / Inner Diagnostics

0x0000 0020OperationLevel / SymbolicId

0x0000 0040OperationLevel / LocalizedText

0x0000 0080OperationLevel / AdditionalInfo

0x0000 0100OperationLevel / Inner StatusCode

0x0000 0200OperationLevel / Inner Diagnostics

Each of these values is composed of two components, leveland type, as described below. If none are requested, as indicated by a 0 value, or if no diagnostic information was encountered in processing of the request, then diagnostics information is not returned.


ServiceLevelreturn diagnostics in the diagnosticInfoof the Service.

OperationLevelreturn diagnostics in the diagnosticInfodefined for individual operations requested in the Service.


SymbolicId return a namespace-qualified, symbolic identifier for an error or condition. The maximum length of this identifier is 32 characters.

LocalizedTextreturn up to 256 bytes of localized text that describes the symbolic id.

AdditionalInforeturn a byte string that contains additional diagnostic information, such as a memory image. The format of this byte string is vendor-specific, and may depend on the type of error or condition encountered.

InnerStatusCodereturn the inner StatusCodeassociated with the operation or Service.

InnerDiagnosticsreturn the inner diagnostic info associated with the operation or Service. The contents of the inner diagnostic info structure are determined by other bits in the mask. Note that setting this bit could cause multiple levels of nested diagnostic info structures to be returned.



An identifier that identifies the Client’s security audit log entry associated with this request. An empty string value means that this parameter is not used.

The auditEntryId typically contains who initiated the action and from where it was initiated. The auditEntryId is included in the AuditEventto allow human readers to correlate an Eventwith the initiating action.

More details of the Auditmechanisms are defined in 6.5and in OPC 10000-3.



This timeout in milliseconds is used in the Clientside Communication Stackto set the timeout on a per-call base.

For a Serverthis timeout is only a hint and can be used to cancel long running operations to free resources. If the Server detects a timeout, he can cancel the operation by sending the Serviceresult Bad_Timeout. The Servershould wait at minimum the timeout after he received the request before cancelling the operation. The Servershall check the timeoutHintparameter of a Publish request before processing a Publish response. If the request timed out, a Bad_Timeout Serviceresult is sent and another Publish request is used.

The value of 0 indicates no timeout.


Extensible Parameter


Reserved for future use.

Applications that do not understand the header should ignore it.