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

Trends and Challenges for Industrial Communication Systems 67-3
scalability, or low costs. “Universal” networks that can satisfy every possible connectivity need do not
exist, but hybrid networks are getting close.
A hybrid network consists of more than one communication channel, ideally of very diverse
channels. An example is a mobile device with GPRS and GPS. It combines a bidirectional best-effort
channel with a unidirectional information source. Similar thoughts are behind energy management
nodes that use Internet and electricity grid frequency as information sources [FK07].
Another possibility to move toward universal networks is newer developments where features of
several domains were combined. Most notably, this happened on the media access control layer in the
case of networks like IEEE 1394 or IEC 61580. Typically, one part of the bandwidth is reserved for deterministic
traffic (i.e., isochronous slots), while the rest of it can be arbitrated in a CSMA way as many
other networks do. With this hybrid design, two very different network qualities can be achieved: Easy
scalability for non-real-time services and guaranteed service for real-time applications.
An important factor for hybrid designs is how quality of services (QoS) is implemented. As surely, the
IP suite will play a continuously important role in ICS, it is good to know that version 6 of IP addresses
QoS. Although one (especially an ICS) can still feel v4’s problems in v6, it has at least (beside its oftenmentioned
better scalability) flow labeling, better priorities, and is prepared for extended headers that
might contain additional QoS information. Surely, the designers of IPv6 QoS had multimedia services
in mind, but ICS are also sensitive to (all four aspects of) QoS:
• Bandwidth
• Latency (packet delay)
• Latency variation (jitter)
• Packet loss
Bandwidth might be the least important aspect in 80% of all industrial communication (especially
automation) cases, but robot vision and image processing is on the rise at the shop floor. Also, the size
of installations and the number of nodes is dramatically increasing, so bandwidth will play a larger role
than up to now where an IP network over 100 Mb Ethernet will practically never experience a bandwidth
problem in an automation environment. Latency and jitter are most important for network-based
control where guaranteed timely behavior is required. Especially, time synchronization—a very important
service in distributed systems (think of system diagnostics in process control or multimedia)—
needs accurately defined upper boundaries for latency. Packet loss is no problem for media streams but
counted quantities during production or emergency shutdown messages demand high availability and
reliability of the ICS. It is to be expected that QoS will play a more prominent and visible role in the
future of ICS. The existing proposals and implementation of IPv6 QoS is certainly not sufficient for ICS
and we have to work on suitable extensions, probably via its flexible header.
67.5 M2M Communication
Machines are—and will increasingly be—used to act on behalf of humans. In the past, this meant physical
labor; nowadays, it is more and more decision making and “softer” tasks. Computer programs that
act on behalf of certain individuals or roles are commonly called software agents. Just like humans, software
agents need to communicate with other agents, the environment, and humans to be able to fulfill
their tasks. Unlike humans, however, they are not legal and physical person with an associated identity
and trust. This is a very important distinction when it comes to information security.
Most existing security measures rely on cryptographic methods to satisfy security needs like authenticity
or confidentiality. The security problem is boiled down to protecting a certain cryptographic key
during setup and operation. If the end points of the respective communication relation are humans,
this key—which provides identity and confidentiality—might be protected with personal identification
numbers (PINs) or other “side channels,” which can only be provided by the intended person.
Transferring these established procedures to M2M communication is not trivial. The only affordable
© 2011 by Taylor and Francis Group, LLC