The FL-net: Japanese Quality Standard

The term FL-net stands for a protocol which is used in automation technology. It was developed based on an initiative for standardization by the Japan Electrical Manufacturers Association (abbreviated as JEMA) and some other Japanese companies. FL-net also is equated with the controller level network, i.e. the control unit inside a system. This is based completely on the specifications from ‘device-level network’ OPCN-1. This also is a Japanese technology. FL-net operates on the basis of the industrial Ethernet. This is an application that makes it possible to specify software components (such as protocols) with parts of the hardware (e.g. the cables, distributors, or network cards) as well as for cable-bound data networks. The selected software and hardware is actually LAN technology, i.e. local networks, which however, are also capable of creating a data exchange via the Ethernet where they send all forms of data packets among each other and as such, communicate. In addition to the purpose of automating production processes, it also has the task of predicting faults so as to prevent down time or failure of the system. Accordingly, the FL-net also was conceived to establish a communicative connection between the control methods, e.g. CNC or PLC. Here, CNC stands for computer-aided numerical control and PLC stands for programmable logic controller (known as SPS in German).

Specifications for the FL-net

As has already been mentioned, this protocol is based on Ethernet technology. However, there are also differences between these two technologies. The most far reaching one is the ability to guarantee stable and secure transmission times for the transmission of data. In other words, this concerns the aspect of real-time-enabled data transmissions. With the FL-net, this is done by using a connection protocol that ensures good real-time transmission in connection with UDP/IP. A unit from this protocol is installed in a control unit and as such, it transmits and receives critical data concerning the status and the processes within a network. This is done simply by assigning an address, i.e. an accurate position at which the subscriber is located in the system. This has the advantage that during the communication, other subscribers know directly where a unit is located and which message is to be transmitted to it. Naturally, this also facilitates the finding and solving of problems and faults, as the subscribers can be easily identified and addresses can be clearly assigned.

The Topology of the FL-net

Topology is generally the designation for a structure occurring within a computer network. It shows the mutual connections between several devices within the system. These couplings serve the task of data exchange. The topology occurring with a network decides how the reliability is structured. This way, if there are alternative paths between the nodes, when a participant fails, it is possible to ensure that the functionality of the system is maintained and down-time is prevented. As such, such bypasses can always be found in a topology in addition to the conventional work paths. Knowledge of the type of the network structure also can serve for assessing a rendered service. This helps in making the selection of correct investments and suitable hardware. Normally, in differentiating the structures, a difference is made between

  • the physical topology which describes the set up of the wiring and
  • the logical topology which shows the data flow between the terminals. Flexible structures are found within the FL-net. Thus, the star topology, the tree topology, and the line topology may occur here.
  • Star topology - here, within the FL-net, all other subscribers are connected by a two-point connection to a central participant. In selecting the central subscriber, it should be noted that it does not necessarily have to have a higher control intelligence. Among other things, the advantages of this arrangement include the possibility of being able to easily expand the network as well as reaching high transfer rates. It is also well suited for use in the multicast and broadcast sector.
  • Tree topology - this networking is characterized by a root which marks the first or topmost node. At least one, but in most cases several edges start from this position. These are also called links. These links continue the structure to a leaf, the end node, but they also may connect to the root or another tree topology, i.e. the graph theory. The advantages of this arrangement in the FL-net lie in the fact that the failure of a terminal has no consequences, the structure can be expanded, long distances and extensive combinations can be realized and that it is suited to search and sorting algorithms.
  • Bus topology - this arrangement within FL-net is also called a line structure. This is because all devices are connected directly to the bus which functions as a transmission medium so that there are no active components between the devices and the medium. The network runs as a visual representation in a row. Here as well, failure of a device has no consequences for functionality. Furthermore, the use of such a structure can reduce the quantity of the required cable. This is something which minimizes the costs.