Image Processing Reference
In-Depth Information
Network protocols utilize different approaches to provide end-to-end data delivery. he differen-
tiation could be at the lowest physical level (e.g., wired vs. wireless) up through the mechanism at
which network access is negotiated, all the way up through application services that are supported.
Protocol functionality is commonly described and differentiated utilizing the International Stan-
dards Organization-Open Systems Interconnection (ISO-OSI) seven-layer reference model [].
The seven layers are physical, data link, network, transport, session, presentation, and application.
The network protocol, specifically the media access control (MAC) protocol component, defines
the mechanism for delegating this bandwidth in such a way so that the network is “optimized” for
a specific type of communication (e.g., large data packet size with low determinism vs. small data
packet size with high determinism). Over the past decade “bus wars” (referring to sensor bus network
technology) have resulted in serious technical debates with respect to the optimal MAC approach for
different applications [,].
Over the past years, however, it has become more and more evident that the pervasiveness of
Ethernet, especially in domains outside of manufacturing control (e.g., the Internet), will result in its
eventual dominance in the manufacturing control domain [,,]. his movement has been facili-
tated in large part by the emergence of switch technology in Ethernet networks, which can increase
determinism []. While it is not clear yet whether or not Ethernet is a candidate for safety network-
ing, it is a strong contender in the control sub-domain, and has achieved dominance in diagnostics
networking [].
Even more recently, there has been a strong trend toward consideration of wireless as the networking
medium at all levels to support all functionalities. his trend is just beginning to take shape, though,
and it is not clear to what extent wireless will successfully supplant wired technologies. It is the authors'
opinion that a large portion of Ethernet solutions, especially at the higher levels, and in the domains
of diagnostics and, to a lesser extent, control, will be replaced by wireless over the next decade [].
The body of research around control networks is very deep and diverse. Networks present not only
challenges of timing in control systems, but also opportunities for new control directions enabled by
the distribution capabilities of control networks. For example, there has been a significant amount of
recent work on networked control systems (NCSs) [,]. Despite this rich body of work, one impor-
tant aspect of control networks remains relatively untouched in the research community: the speed of
the devices on the network. Practical application of control networks often reveals that device speeds
dominate in determining the system performance to the point that the speed and determinism (net-
work QoS parameters) of the network protocol are irrelevant [,,]. Unfortunately, the academic
focus on networks in the analysis of control network systems, often with assumptions of zero delay
of devices, has served to further hide the fact that device speed is often the determining factor in
assessing the NCS performance.
In light of the strong and diverse academic and industry focus on networks as well as the myriad
of network technologies, the prospect of choosing a “best” network technology for a particular envi-
ronment is ominous. he choice should be governed by a number of factors that balance upfront and
recurring costs and performance to an objective function that best fits the particular environment.
Thus, the best solution is necessarily application dependent []. A methodology is needed that sup-
ports the application of theory, experimental results, and analytics to a particular application domain
so that the trade-offs can be quantified and a best solution determined [].
This chapter explores the application of NCSs in the domains of control, diagnostics, and safety in
manufacturing []. Specifically, Section . explores the parameterization of networks with respect
to balancing QoS capabilities. his parameterization provides a basis for diferentiating industrial net-
work types. Section . introduces common network protocol approaches and differentiates them
with respect to functional characteristics. The importance of device performance is also explored.
Section . presents a method for NCS evaluation that includes theoretical, experimental, and
analytical components. In Section ., network applications within the domain of manufacturing
are explored; these include application sub-domains of control, diagnostics and safety, as well as
