You can install the port server software on a Geo SCADA Expert server or remote PC to enable multiple PSTN channels to share a single modem. This is useful when there are limited modem resources available.
There are 2 topologies for modem sharing:
- Geo SCADA Expert server using port server for modem sharing
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- Remote PC using port server
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The port server setup for modem sharing works as follows:
- The Geo SCADA Expert server communicates with the Port Server software via a TCP/IP link. The TCP/IP link can be a connection to a remote PC that runs the Port Server software or can be a link within a Geo SCADA Expert server.
- The Port Server software enables a modem that is connected to a serial port on the Geo SCADA Expert server/remote PC to be shared by multiple PSTN channels.
- The modem communicates with the outstations and other devices.
You have to configure PSTN channels for each connection to the modem (one channel for each connection that is to share the modem). Set the PSTN channel configuration for the PSTN channels to share the modem. Only configure one dial-in channel (otherwise the channel will fail).
If a channel attempts to make a call while the modem is being used by another channel, the call attempt will fail and a 'blocked' error will be logged. However, the number of call attempts will not increment, and the call will be retried as many times as required until it succeeds, fails, or the requests timeout elapses. The requests timeout is defined on the Drivers section of the Server Configuration Tool (see Define the Driver Request Timeouts).
When the port is not being used, it uses the port settings/modem command of the dial-in channel (if any) to prepare itself for any incoming calls.
To set up the port server to provide modem sharing facilities:
- Install the port server on the Geo SCADA Expert server or remote PC as required (see Install the Port Server Software).
- In Geo SCADA Expert, configure a PSTN channel for each driver that will share the modem. Configure the channels to have the following settings:
- Connection Type set to Remote Serial
- Node Name set to:
- localhost (when the port server is installed on the Geo SCADA Expert server)
- The name/address of the remote PC (when the port server is installed on a remote PC).
- Port set to the same port on each channel (this should be the port to which the modem is connected)
- Shared setting enabled.
Each channel can, if necessary, have different port settings (Baud Rate, Data Bits, and so on). The port server will change the port settings as required before each outgoing call. Similarly, the channels can also have different modem commands (the port server will change the modem command as required).
To be able to support sharing, your modem has to be able to connect with each of the outstations, PLCs, and other devices that are to use the modem. Some devices, particularly older outstations, require the modem to be set up in such a way that the modem is unable to be shared (as the modem’s configuration means it cannot connect to other devices).
For more information, see Create the Channels in the Database.