Restrictions for Use
The following restrictions apply to OPCNetView:
- OPCNetView can only report connections if DCOM has been configured to use TCP/IP as the
network protocol for communicating with a remote node. TCP/IP is the default network protocol and rarely changed.
- Even when DCOM is configured to use TCP/IP for connections, DCOM initiated connections between 2 processes
running on the local node will not use TCP/IP. That means that OPCNetView does not yet support reporting network
connections between a local OPC Client and local OPC Server. In reality, it is very rare for the same node to be
used for OPC clients and OPC servers so this should not be a restriction in most cases.
- If an OPC Server is actually an in-process DLL, loaded by the client, TCP/IP will not be used for communications
between the client and server. That means that OPCNetView does not yet support reporting communications between
those processes. Again, this is very rarely the case.
- As explained in Philosophy of OPCNetView, OPCNetView reports the number of Windows network connections between
remote OPC processes. These network connections are handled by DCOM and generally provide a good indication of the
number of OPC connections between the OPC processes. The two are not always exactly the same however and the number
of network connections created by DCOM depends on a number of complex factors such as which OPC functions were used
to establish the connection, whether the client uses different threads for concurrent connections and whether the
interface is marshalled or unmarshalled. The following situations may be observed around the time when an OPC
connection is established or disconnected:
- An OPC connection can result in DCOM creating an extra network connection, which will often wither away
after a period of time.
- DCOM optimises network connections and so they may persist for a while after the OPC connection has been
disconnected (assuming both OPC processes are still running). DCOM will re-use a network connection however if
another OPC connection request is made within a reasonable time period. Hence, for example, the number of
network connections shown in OPCNetView for an OPC Client which establishes an OPC connection, reads,
disconnects and then hibernates for 30 seconds will appear static.
- If you are running as a user without administrative privileges, the view of remote nodes may be restricted.
Only nodes that have been previously interrogated by a privileged user in the past can be investigated.