IEC 62541-6:2020 specifies the OPC Unified Architecture (OPC UA) mapping between the security model described in IEC TR 62541-2, the abstract service definitions specified in IEC 62541-4, the data structures defined in IEC 62541-5 and the physical network protocols that can be used to implement the OPC UA specification. This third edition cancels and replaces the second edition published in 2015. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) Encodings: ' added JSON encoding for PubSub (non-reversible); ' added JSON encoding for Client/Server (reversible); ' added support for optional fields in structures; ' added support for Unions. b) Transport mappings: ' added WebSocket secure connection ' WSS; ' added support for reverse connectivity; ' added support for session-less service invocation in HTTPS. c) Deprecated Transport (missing support on most platforms): ' SOAP/HTTP with WS-SecureConversation (all encodings). d) Added mapping for JSON Web Token. e) Added support for Unions to NodeSet Schema. f) Added batch operations to add/delete nodes to/from NodeSet Schema. g) Added support for multi-dimensional arrays outside of Variants. h) Added binary representation for Decimal data types. i) Added mapping for an OAuth2 Authorization Framework.