Applies To:
  • CitectSCADA 3.x 4.x

How do you set up RAS with Microwave modems and RAS? 

The direct connection of modems to Citect is not recommended any more. It has too many problems associated with it, with different kinds of modems ( Compression, high speed modems ). Citect recommends Remote Access Server ( RAS ) as a means of remotely connecting Citects on a serial line. The configuration for RAS follows.
  1. Add a RAS box ( Cisco, Accton, Lanrover or any other good brand ) between the Host Citect and the Modem connected to it. The RAS box has an ethernet port and at least 1 serial ( RS232 ) port.
  2. The "Host" Microwave modem is connected to the Serial port on the RAS box.
  3. The Remote Citect will be connected to the "Remote" microwave modem via the computer RS232 serial port.
  4. MS Windows 95 can be used on all Citect stations as the operating system. At the "Host", Win95 will be configured to log into the RAS box over the serial radio microwave link.
  5. Citect will use this serial link to request data from the Citect servers. The Citect database and all graphic pages will be on local C drives. Only data will be transmitted.

The Microwave modems will have to have an RS232 port, which can handle at least 9600 baud full duplex. If a higher baud rate between the Modem and RAS is possible, it should be used. The data rate of the Microwave link should be at least 9600 BPS for adequate updates on the remote Citect.

The modems should behave like normal telephone type modems, and should also have error checking and compression, to increase bandwidth. Try to write out responsibility for the modems and Radio link, as usually, these cause the most problems and are out of our control.

To be sure that Citect will work over the Microwave link, details from the microwave manufacturer have to be sorted out. The customer is probably the best to sort this out, as they would now the manufacturer or the agent for this stuff. A question for the manufacturer could be, "Does his ( or her, being politically correct ) system support RAS"?

The basic criteria for Citect to transmit data over radio follows

Serial Interface : EIA RS232, DCE, Serial async, 9600 - 19200 Baud, 7/8 Bit, No/odd/even parity. ( This is the port on the modem which Citect connects to )

Data Rate : 9600 BPS ( This is the rate the radio transmits its data )

Modem Properties : The modem should be capable of transmitting data over the radio channel, being full duplex, the reciprocal process is performed simultaneously, including clock recovery.

To be sure, the customer could be asked to supply sample units for testing. Another way is to ask the customer to test the RAS link through the Radio link. If RAS works, then Citect will work.