How IFSF Works
IFSF is more complex but more comprehensive than most proprietary protocols. The IFSF protocol has two independent layers; a device application protocol layer and a communications protocol layer. The application protocol is independent of the underlying communications layer. The communications protocol specification makes the link to the transport layer.
At the communication layer, LonWorks has been predominantly deployed because existing cables and cabling topology can be reused. Methods have been defined to use TCP/IP, but this requires higher specification cable and a point to point topology, and is therefore more suited to green field or rebuild service stations; in practice it is relatively rare.
The IFSF standards define messages sent and received by each type of device. The messages are designed to be expandable by specifying individual fields with types and lengths. The messages are grouped into various "databases" for the logical parts of each device, such as a nozzle at a pump.
Each type of device (dispenser, tank level gauge, price sign, carwash, etc) defines its own set of databases and fields. Most devices also define a state machine to control the operation of the device. For example, the Dispenser device has the following states:
- Inoperative (during startup)
- Closed (not allowed to sell fuel, but otherwise working)
- Idle (normal operating state)
- Authorised (nozzle in, but authorised for the next delivery of fuel)
- Calling (nozzle out, not yet authorised)
- Started (nozzle out and authorised, but no fuel flowing yet)
- Suspended started (paused, before fuel flow)
- Fuelling (fuel flowing)
- Suspended fuelling (paused, during fuel flow)
Read more about this topic: International Forecourt Standards Forum
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