The underlying technology

In a project, there are several components used to implement the Thin Client capability.

These components are:

Data Server

The Data Server is built-in to the AVEVA Edge runtime. The Data Server has direct access to the Project Tags Database (runtime) and is responsible for working with ISSymbol to make sure any Tag data being displayed on a Web page at any Thin Client is updated with the latest value(s).

AVEVA Edge can support a backup or secondary Data Server that will be used should the Primary Data Server become unavailable. The Thin Client will automatically switch over to the Secondary without user intervention required.

Web Server

The Primary Web Server is responsible for providing Web pages on demand (that is, when requested by the Client) through navigation to various project screens by the Thin Client. The Web Server communicates with the Thin Client via HTTP protocol over TCP/IP. SSL (Secure Socket Layer) encrypted communications can be enabled. The Web Server does not need to reside on the same PC as the AVEVA Edge runtime project. In fact, the Web Server could be a non-Windows corporate Web Server. However, the Web Server needs to have access to the HTML files that are the project Web pages.

AVEVA Edge supports a Secondary Web Server that will be automatically switched to (by the Client) in case the Primary Web Server becomes unavailable.

Web Browser

The Web Browser is located on the Thin Client PC and provides the graphical interface function with the user. Web pages (HTML) is passed to the browser via demand ("pull") and data is "pushed" to the browser by the Data Server whenever a Tag or Tags referenced on the Screen displayed on the Web Client is updated in the Tag Database.

ISSymbol

ISSymbol is a AVEVA-provided ActiveX Control that facilitates the interaction between the browser on the Web Client and the Web Server as well as the Data Server. There are ISSymbol ActiveX Control versions for Windows and all Windows Embedded platforms.

The ISSymbol ActiveX Control is used for both the Internet Explorer-based and Secure Viewer-based browsers.

Web Tunneling Gateway

The (Primary) Web Tunneling Gateway is a bridge between the Web Server and the Data Server that is used in one of two situations. The first is whenever data security is required (for example, AVEVA Edge data exchanged with the Thin Client needs to be encrypted). The second situation is when the Data Server is hidden behind a corporate firewall, and only the Web Server IP address (or URL) is exposed.

AVEVA Edge supports a backup (Secondary) Web Tunneling Gateway to be used if the Primary Web Tunneling Gateway becomes unavailable. The Thin Client will automatically switch over to the secondary Web Tunneling Gateway.

The Web Tunneling Gateway is automatically installed when AVEVA Edge is installed on your PC if the installation program detects that IIS is present.

Notes

• The Web Tunneling Gateway is automatically installed if IIS is detected during the installation process. Otherwise, it must be manually installed.

• The main function of the Web Tunneling gateway is to encapsulate data packets in HTTP or HTTPS for communication through a firewall.