NodeId values shall be encoded as a JSON string using the format defined in 5.1.12. NodeIds in NamespaceIndex 0 use the <identifier> form. All other NodeIds use the <namespace-uri> form.

The first abnormal state occurs when the encoder cannot map a NamespaceIndex to a NamespaceUri. In this case, the encoder shall encode the NamespaceIndex using the <namespace-index> form. The decoder shall pass this NamespaceIndex to the application.

The second abnormal state occurs when the decoder cannot convert a NamespaceUri to a NamespaceIndex. If this occurs the decoder shall set the NamespaceIndex to 0, the IdType to String and the Identifier to the JSON string.