System architecture

To display a live CitectSCADA project in an Internet browser, you need to combine the content of the project pages and the current data these pages present using standard, Web-based communication protocols. To understand the communication architecture for the CitectSCADA Web Client, it's easiest to consider the role each of the following components play in achieving this outcome:

• CitectSCADA Web Server - Performs the server-side functionality of the system. It operates by accepting requests from the client, and providing a response to the client when the clients details are authenticated. It then directs a client to the graphical and functional content of a CitectSCADA project and the location of the runtime servers. This information is stored on the Web Server when a CitectSCADA project is configured as a "deployment". A CitectSCADA Web Server can contain multiple deployments.
• CitectSCADA Runtime Servers (including the I/O Server, Alarm Server, Trends Server and Reports Server) - Monitor the physical production facility and contain the live variable tag data, alarms and trends that the Web Client will display.
• Web Client - provides the platform to merge a deployed project's pages and content with the raw data drawn from the runtime servers. Again, standard Web technologies are necessary, so the client uses Microsoft Internet Explorer.

The following diagram shows how these components interact.

CitectSCADA Web Client communications architecture.

Once the Web Client has connected to the Runtime servers, steps 2 and 3 become an ongoing process, with the necessary content being called upon as the user navigates the project pages.

The citect.ini file settings used by a Web Client are taken from the citect.ini file on the Web Server at the time of connection.

This diagram has the system components set up on different computers purely for the sake of explaining the communications model. In reality, the flexibility of the architecture allows these components to be distributed in any necessary arrangement; they can even share a common location.