wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

34
WorldFip
Francisco Vasques
University of Porto
Orazio Mirabella
University of Catania
34.1 Introduction.....................................................................................34-1
34.2 Physical Layer...................................................................................34-2
34.3 Data Link Layer...............................................................................34-2
Transmission of Cyclic Traffic. •. Bus Arbitrator Table. •. .
Transmission of Asynchronous Traffic
34.4 Application Layer............................................................................34-6
34.5 Timing Properties of WorldFIP Networks..................................34-7
Concept of Producer/Distributor/Consumer. •. Buffer Transfer
Timings. •. Bus Arbitrator Table. •. WorldFIP Aperiodic Buffer
Transfers. •. Setting the WorldFIP BAT: Rate Monotonic Approach
References..................................................................................................34-18
34.1 Introduction
WorldFIP is a fieldbus that has been mainly designed for time-critical applications featured by periodic
processes. Its name comes from the fieldbus instrumentation protocol that was initially standardized as
French national Standard and subsequently included into the European Fieldbus Standard CENELEC
EN50170. The name has been changed into WorldFIP to make it more attractive for the international
market.
The basic idea behind WorldFIP is to consider all variables relevant to the application process as
a distributed database that is periodically refreshed in order to maintain the values of the updated
variables. This provides a deterministic framework for the exchange of process variables produced by
sensors, processed by PLCs or process computers, and consumed by actuators. The new concept of
producer/consumer, as opposed to the traditional client/server concept, was introduced first time in
WorldFip.
As the fieldbus must carry not only periodic process variables (which are usually a few bytes long) but
also management data (e.g., configuration files), which can be very long, different kinds of traffic must
be considered:
• Periodic traffic for the updating of process variables. In WorldFIP-based applications, it is
assumed that about 99% of traffic belongs to this category.
• Aperiodic traffic for the exchange of process variables.
• Aperiodic traffic for the exchange of messages. This last kind of traffic is generated by management
files, which according to their dimensions must be handled in a different way with respect
to process variables.
The layered architecture adopted in WorldFIP is based on only three layers (as shown in Figure 34.1),
which is usual for real-time networks: physical layer (PHL), data link layer (DLL = medium access control
[MAC] + logical link control [LLC].), and application layer (AL).
34-1
© 2011 by Taylor and Francis Group, LLC