MessageChunksare sent as they are encoded. MessageChunksbelonging to the same Messageshall be sent sequentially. If an error occurs creating a MessageChunk then the sender shall send a final MessageChunk to the receiver that tells the receiver that an error occurred and that it should discard the previous chunks. The sender indicates that the MessageChunk contains an error by setting the IsFinal flag to ‘A’ (for Abort). Table 46specifies the contents of the Messageabort MessageChunk.

Table 46– OPC UA Secure ConversationMessage abort body


Data Type




The numeric code for the error.

This shall be one of the values listed in Table 55.



A more verbose description of the error.

This string shall not be more than 4 096 bytes.

A Clientshall ignore strings that are longer than this.

The receiver shall check the security on the abort MessageChunk before processing it. If everything is ok, then the receiver shall ignore the Messagebut shall not close the SecureChannel. The Clientshall report the error back to the application as StatusCodefor the request. If the Clientis the sender, then it shall report the error without waiting for a response from the Server.