User Manual

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Building Technologies MM8000 OPC Connectivity Configuration Guide
Fire Safety & Security Products 06.2007
5 DCOM settings for OPC communication
The communication infrastructure for OPC over a network is called DCOM.
DCOM (Distributed Component Object Model) is a Microsoft Windows inter-
process communication framework in which client programs can request services
from server programs - on other networked computers - through a defined set of in-
terfaces. DCOM is based on the Component Object Model (COM), which provides
a set of services allowing clients and servers to communicate within the same com-
puter.
DCOM security
DCOM includes a security configuration and, in order to set up a networked OPC
connection, you need to acquire some understanding of Windows security, and in
particular the Distributed COM Configuration tool (DCOMCNFG), which defines the
security model for COM applications used remotely.
When a COM server is run remotely, it can run as the 'interactive user', i.e. the user
who is currently logged in, or under the identity of a special user, whose account is
created specifically for the purpose of running the OPC server.
In the case of MM8000, this user is normally called “DMS8000_PROC” (this is the
default setting, refer to MM8000 Installation, Configuration, and Commissioning
manual or ICC, doc. A6V10062413). In fact, in MM8000, all services run under the
identity of this “internal” user, rather than as the “interactive user” or the “launching
user”.
In order to properly communicate with MM8000, the OPC server computer must
authorise the MM8000 internal user to access the entire server computer, or at
least the OPC server software task, in the “DCOM Config” list.
On the other hand, it is also necessary that the user running the OPC server (that
you need to identify in the server documentation) is granted access to the entire
MM8000 computer or at least to the “MM8000server” software task.
User definition
If the server and client computers run in a common Windows domain, then the us-
ers are defined at domain level and therefore visible from all machines.
Instead, if a network workgroup is used, then the users involved in the OPC and
DCOM settings must be defined locally on each machine, using exactly the same
username and password.
On the MM8000 PC, the internal user called “DMS8000_PROC” is automatically
defined. If not available at domain level, the same user must be manually added in
the OPC server PC.
Similarly, the user associated to the OPC server’s identity may have to be added to
the MM8000 Windows user list.
DCOM Configuration tool
The DCOMcnfg application allows setting the DCOM security parameters involved
in network OPC links. In other words, this application permits you to add a user to
the list of the ones allowed to access and launch any task or a specific task.
In order to run the application, click the “Start” button and then “Run”. At this point,
in the small window that appears, type “DCOMcnfg” and then “OK”.
On Windows XP SP2 machine, the “Component Services” window opens (Fig 46).