Server Side
(ASP.NET, ASP, PHP etc.)
This is where the Web Server (such as IIS) dynamically builds the page when the browser requests it.
For example:
A user requests a web-page which will read a value from a Device. The Web Server will read that value from the device and will dynamically embed that value within the web-page as plain text. A static HTML page is then downloaded to the browser. The user must refresh/reload in order to see up to date data
Pros and cons:
Pros are a central I/O system with a single (controllable) connection to your OPC Server(s).
Cons can be with scalability, but this is very specific to the design of the web-application and its design. The more clients that require the page(s), the more work your web-server (IIS) will be responsible for. The OPC Web Client will actually assist with scalability as it uses a back-end engine to cache data, which results in a much more responsive system.
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Client Side
(VBScript, JScript etc.)
This is where a web-page is downloaded to the browser (such as IE) and any code required for the page to run will run within the browser itself. The web-server acts like a file-server only.
For example:
The browser could maintain its own connection to the OPC Server directly. Reads/writes could occur in real-time and without page-refreshes.
Pros and cons:
Pros are the ability for the workload to be moved to the browser instead of the web-server, this allows for some scalability.
There are 2 Cons in particular:
- Security within the browser is tight and requires user configuration to permit the use of an ActiveX to run.
- Each browser maintains its own connection to the OPC Server(s) which could add greater overhead to your OPC Server(s) and PLC Device(s).
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