Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00 4.00 4.10

I am using Citect LAN redundancy with 2 network cards. I am running Windows 95 clients talking to a Windows NT file server. My project is installed on the file server. When I disconnect the LAN card that Citect is communicating with, Citect will switch over to the second network card and continue to communicate correctly. However the next time I change pages Citect will pause for 30 seconds. After the pause Citect will run normally. What is causing this pause? 

The pause is being caused by the time out of the file redirector. When you disconnect the network card, Citect will detect the failure and will swap to the second card. As your project is installed on the network file server, each time you display a page Citect will get various files from the file server. So when you change pages Citect will call to Windows to open a file. This request will go to the redirector to be sent to your file server. The redirector was communicating to the file server over the network card you have just disconnected so this request will time out and fail. The redirector will now try to re-establish the connection to the file server, so it will first try again on the first LAN card and then on the second card. Once the redirector has established the connection via the second card, Citect will be able to read the files and the page will change. Citect has no choice but to wait for the redirector to time out and retry.

The time out and retries for the redirector have been tuned to cope with a wide variety of networks. So they tend to be far greater than is required for a high performance network. If your reduce these time out then the delays in Citect will be reduced. Your other solution is to copy your project files to the local hard disk.

CIT has confirmed this to be a problem in the Microsoft redirector. For a solution see Q1949.