Applies To:
  • CitectSCADA 4.00, 5.00
Summary:
I want to build a Citect system with Dial-up facilities. That is, I want to be able to allow operators to dial into a Citect system from home and have a look at the state of the plant. How can I do this? 

Solution:
A while back, there was really only one way to do this - Cinet! CiNet was developed by Ci Technologies because there was no other suitable remote access solution available. Now that Microsoft's Dial up Networking (RAS) has matured we have decided not to do any more development on CiNet, and therefore it is suggested that our customers make use of this new method. Other remote access systems which provide a similar wide area network connection such as Shiva and 3Com may also be suitable.

Dial up Networking is a Microsoft technology which allows transparent access to a remote LAN using modems. In fact it has nothing to do with Citect. You can use it to allow basic file and print access just like on a normal office LAN. However, since it supports the protocols typically used in Citect networked solutions, Dial up Networking is a simple solution to most requirements. Many types of wide area communications hardware can theoretically be used with Dial up Networking. This includes dial up modems, leased line drivers and microwave modems. ISDN modems should also work. Considering this, the name 'Dial up Networking' is a bit of a misnomer.

Since Dial up Networking is integrated with Windows 95 and NT, security issues are automatically taken care of. Also, the link can be tested before Citect is even started. Remote machines are rendered visible to those connected directly to the LAN, and vice-versa. It should also be possible following this train of thought to 'see' other remote machines from a dial in client. This hasn't been tested by CiT however.

There are a few other issues to be considered. Some tuning may be required to achieve acceptable performance. Considering the extra delay involved, machines communicating over a Dial up link require a modified [LAN]SendTimeout parameter (say 60000) to allow for slow transmissions. Other causes of slower network traffic (PiggyBackAcking etc) need to be eradicated for the best possible performance. Citect v4.20 and following have taken care of this for the user. Finally, Dial up Networking does not properly implement NetBIOS group names which Citect uses for client/server session communication. The workaround for this is to turn off the use of group names by Citect (set [LAN]Groupname=0) and ensure that each node has a unique [LAN]Node setting. Ordinarily this setting is not used especially much.

The setup of Dial up Networking allows the administrator to 'turn off' certain protocols. This means that the server (the machine dialed into) will not forward messages contained in certain protocols to the remote client. If the remote client can see LAN based resources (files or printers) but will not establish a Citect session this may be the reason. Ensure the protocol Citect is trying to use is being allowed through the dial up server.

Experience with RAS or Dial up networking has shown that using the implementation which comes with Windows for Workgroups is a little perilous and should probably be avoided. Stick with homogenous operating system connections and use at least Windows 95. Windows NT is preferred.

This article is basically a summary of other KBase articles. Consult Q1174, Q1338

 
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