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

53-14 Industrial Communication Systems
OCARI
router
WirelessHART
access point
OCARI PAN
coordinator
WirelessHART
gateway
Industrial backbone
Wireless sensors network oriented middleware
Comm.
manager
Virtual
sensor
manager
Publication
manager
Persistent
data
manager
Database
SCADA
Centralized
network
monitoring
Software bus (publish/subscribe)
FIGURE 53.13
Middleware is the key for the integration of different protocols.
layers are not the same, making it impossible for either network to directly carry signals from the other.
This means that gateways are needed to ensure interoperability and extensive research must be done
in the development of new middleware paradigms. Middleware is understood as an abstraction layer
that can be used to program applications in a network-transparent way. The high level of abstraction
that is provided lowers the cost of development of control applications. Middleware is a generic name
used to refer to a class of software whose purpose is to serve as glue between separately built systems
(Figure 53.13).
However, the ISA100 committee is intended to be a single “universal” network for the wireless
transport of information from all types of industrial wired protocols and a new subcommittee for the
ISA100.11a and the WirelessHART convergence, called ISA100.12, has been created. The aim is not only
to ensure coexistence of nodes of both kinds but also to make possible the cooperation between the
two networks. Proposals like dual-mode gateways and a dual-mode node are under discussion. From
the physical point of view, collisions will arise when different networks operate in the same area, especially
in a crowded environment like the ISM band around 2.4.GHz. However, data delivery model of
industrial communications must be considered, i.e., a cyclical exchange of a small quantity of information
(i.e., determinism and often isochronisms is required but the average bandwidth is low). Both
ISA100.11a and WirelessHART utilizes CCA to avoid collisions with other nonsynchronized systems,
while frequency agility together with a short time-synchronized communications minimizes the bandwidth
occupation and ensures successful data exchange since messages can be resent on other (free)
channels exploiting automatic repeat query (ARQ) error control strategy.
Another important aspect is security. Both ISA and HART solutions include a security manager
to manage and authenticate cryptographic keys. In particular, during normal operations, secret symmetric
keys known to both the sender and the receiver are used. During the commissioning phase,
© 2011 by Taylor and Francis Group, LLC