The Hello Message has the additional fields shown in Table 69.
Table 69 – OPC UA Connection Protocol Hello Message
|
Name |
Data Type |
Description |
|
ProtocolVersion |
UInt32 |
The version of the UACP protocol requested by the Client. If Server does not support the requested version or any lower version it rejects the Client by returning Bad_ProtocolVersionUnsupported. If the Server supports the requested version or a lower version it shall return the version it will use in the Acknowledge Message. The ProtocolVersion for this version of the standard is 0. |
|
ReceiveBufferSize |
UInt32 |
The largest MessageChunk that the sender can receive. Shall be at least 1 024 bytes if the sender intends to use an ECC SecurityPolicy. Shall be at least 8 192 bytes otherwise. |
|
SendBufferSize |
UInt32 |
The largest MessageChunk that the sender will send. Shall be at least 1 024 bytes if the sender intends to use an ECC SecurityPolicy. Shall be at least 8 192 bytes otherwise. |
|
MaxMessageSize |
UInt32 |
The maximum size for any response Message. If MessageChunks have not been sent, the Server shall return an Error Message with a Bad_ResponseTooLarge error if a response Message exceeds this value. If MessageChunks have already been sent the Server shall abort the Message as described in 6.7.3. The Message size is calculated using the unencrypted Message body. A value of zero indicates that the Client has no limit. |
|
MaxChunkCount |
UInt32 |
The maximum number of chunks in any response Message. The Server shall abort the Message with a Bad_ResponseTooLarge Error Message if a response Message exceeds this value. The mechanism for aborting Messages is described fully in 6.7.3. A value of zero indicates that the Client has no limit. |
|
EndpointUrl |
String |
The URL of the Endpoint which the Client wished to connect to. The encoded value shall be less than 4 096 bytes. Servers shall return a Bad_TcpEndpointUrlInvalid Error Message and close the connection if the length exceeds 4 096 or if it does not recognize the resource identified by the URL. |
The EndpointUrl parameter is used to allow multiple Servers to share the same endpoint on a machine. The process listening (also known as the proxy) on the endpoint would connect to the Server identified by the EndpointUrl and would forward all Messages to the Server via this socket. If one socket closes, then the proxy shall close the other socket.
If the Server does not have sufficient resources to allow the establishment of a new SecureChannel it shall immediately return a Bad_TcpNotEnoughResources Error Message and gracefully close the socket. Client should not overload Servers that return this error by immediately trying to create a new SecureChannel.