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.
- 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.
- The "Host" Microwave modem is connected to the Serial port on
the RAS box.
- The Remote Citect will be connected to the "Remote" microwave
modem via the computer RS232 serial port.
- 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.
- 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.
Note:
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.
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