UaExpert
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This page describes discovery and connection options of UaExpert. A simple example can be found here: Step-by-Step Connect Example.
To connect to a server, a client needs information like network address, protocol, and security settings. For this purpose, OPC UA defines a set of discovery features.
All information which is required to establish a connection between client and server is stored in a so-called endpoint. A server can provide several endpoints, each containing
If several OPC UA servers exist, a Discovery Server can be used to provide information of available servers. Servers can register at the Discovery Server. Clients may then request a list of all available servers from the discovery server. The discovery server provides a DiscoveryUrl together with some basic information like the server name.
The DiscoveryUrl is then used to connect to the server and to request the endpoint information using the GetEndpoints service.
OPC UA defines three different discovery options:
The standard OPC UA port is 4840. For local discovery, the client can construct a connection URL with the host name (e.g. opc.tcp://localhost:4840 or opc.tcp://targetHost:4840). This URL is then used to connect to the local discovery server on the host and to call FindServers. If there is only one server on a host, this server will used the standard port and will respond to FindServers with his own information. If several servers are available on a host, a Local Discovery Server (LDS) is used to provide the list of servers as response to FindServers.
The OPC UA Global Discovery Server (GDS) concept allows the configuration of a network wide discovery of OPC UA servers that is not limited to a subnet like mDNS. In addition, it provides functionality for central certificate management including the distribution of CA signed certificates and related Certificate Revocation Lists (CRL) (see also UaExpert GDS registration). A GDS is a complete OPC UA Server and therefore provides the only secure discovery option.
UaExpert provides different type of discovery functionality in the Add Server dialog:
For the selected endpoint the following additional settings are available:
UaExpert supports user authentication via Username/Password and Certificate. These authentication settings can either be selected in the Add Server dialog (see screenshot in the Step-by-Step Connect Example), or it can be chosen later in the Project Window.
Right-click on the Server entry and choose Properties… (if you’re currently not connected to the server) or Change User… (to change the user during an active connection) from the context menu. A dialog for changing authentication settings will open (see screenshot).
Select the radio button next to Username/Password. The users known to Unified Automation’s ANSI C Demo Server are listed in the ANSI C SDK Documentation
Nodes with user based access rights can be found in the folder Objects* → Demo → 005_AccessRights in the server’s address space.
Instead of using the discovery window as described in Step-by-Step Connect Example, the Advanced tab offers to enter connection information directly. If all relevant connection parameters are known, this dialog window can be used to enter the information and skip the discovery process (see screenshot). Furthermore, it is possible to specify a custom name for the session.