The components of this parameter are defined in Table 175.

Table 175 – RequestHeader






Common parameters for all requests submitted on a Session.




The secret Session identifier used to verify that the request is associated with the Session. The SessionAuthenticationToken type is defined in 7.36.



The time the Client sent the request. The parameter is only used for diagnostic and logging purposes in the Server.



A requestHandle associated with the request. This Client defined 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 r esponse 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 0001

ServiceLevel / SymbolicId

0x0000 0002

ServiceLevel / LocalizedText

0x0000 0004

ServiceLevel / AdditionalInfo

0x0000 0008

ServiceLevel / Inner StatusCode

0x0000 0010

ServiceLevel / Inner Diagnostics

0x0000 0020

OperationLevel / SymbolicId

0x0000 0040

OperationLevel / LocalizedText

0x0000 0080

OperationLevel / AdditionalInfo

0x0000 0100

OperationLevel / Inner StatusCode

0x0000 0200

OperationLevel / Inner Diagnostics

Each of these values is composed of two components, level and 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.



return diagnostics in the diagnosticInfo of the Service.


return diagnostics in the diagnosticInfo defined for individual operations requested in the Service.



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


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


return 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.


return the inner StatusCode associated with the operation or Service.


return 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 AuditEvent to allow human readers to correlate an Event with the initiating action.

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



This timeout in milliseconds is used in the Client side Communication Stack to set the timeout on a per-call base.

For a Server this 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 Service result Bad_Timeout. The Server should wait at minimum the timeout after he received the request before cancelling the operation. The Server shall check the timeoutHint parameter of a Publish request before processing a Publish response. If the request timed out, a Bad_Timeout Service result is sent and another Publish request is used.

The value of 0 indicates no timeout.


Extensible Parameter


If additional header parameters are needed, they shall be passed using the AdditionalParametersType defined in 7.1.

Applications that do not understand the header should ignore it.