The term ‘transport’ refers to both the physical communications medium and the low-level logic necessary to drive it. As far as CitectSCADA is concerned, it simply defines how to package a message, how to send it, and where to send it.
The available transport options are usually governed by the kind of ports available on the target I/O Device. However, they are also influenced by the geography of the automation system, specific domain requirements (such as safety, performance, redundancy), and the amount of money the owners are willing to invest.
The three main categories of available transport are:
Of these, Ethernet is by far the transport technology of choice.
Fortunately, by using the concepts of packet encapsulation and intelligent gateway/routing devices, you are able to mix different transport layers. For example, you could use a serial cable from CitectSCADA to a modem, a PSTN line from the modem to another modem, then a serial cable to an Ethernet gateway, and Ethernet to the I/O Device.
Note: Modems are treated as a special case in CitectSCADA since they are recognized as logical devices by Windows. Refer to the specific online help on setting up modems.
CitectSCADA uses the ‘COMx’ driver to implement simple serial transports. Similarly, the ‘TCPIP’ driver implements the Ethernet transport. These are commonly used transport drivers, and both have a range of tuneable options and settings. Each proprietary board has its own specific transport driver – which is typically integrated with the protocol driver.