The AdditionalParametersType parameter is used as value of the additionalHeader field of the RequestHeader and ResponseHeader parameters. It allows Clients and Servers to pass additional named parameters with Service requests or responses. These named parameters may be defined by the OPC UA specification, a companion specification or be specific to a vendor implementation. The name is a QualifiedName which allows the same name to be used in different contexts. The value is a Variant which allows Structures to be passed in addition to basic types such as Strings.

Note that the calls to CreateSession/ActivateSession are made before the Client can read the Server’s current NamespaceArray. This means that only names with a NamespaceIndex of 0 or 1 may be used in the requests for these Services. Companion specifications and vendors can define names in for use with NamespaceIndex 1 if they add prefix that ensures uniqueness. The same restriction applies to values which contain DataTypes with NamespaceIndexes.

The components of this structure are defined in Table 112.

Table 112 – AdditionalParametersType

Name	Type	Description
AdditionalParametersType	structure	Specifies a list of value qualified by a name.
parameters	KeyValuePair []	A list of headers identified by a QualifiedName. The KeyValuePair type is defined in OPC 10000-5.