Industrial Ethernet physical layer design: Questions and answers

Additional answers about an industrial Ethernet network case study and about industrial network design are provided below, after the archived, 1-hour webcast: “A Network Foundation – Applied Case Study in Deploying a Reliable Physical Infrastructure for Process.” A link to the Ethernet network design webcast presentation is provided.

By Mark T. Hoske August 19, 2014

Answers to additional questions about an Ethernet case study and network design are provided below, after the archived, 1-hour webcast, "A Network Foundation – Applied Case Study in Deploying a Reliable Physical Infrastructure for Process." Some audience questions were answered after the presentation and remain part of the archive presentation online. These additional questions and answers wouldn’t fit into the 60-minute time period and are answered below. Link to the webcast is provided, if you haven’t seen it.

Questions covered the networking case study, safety, security, network assessments, cost savings, standards, and IT versus operations, among others. Providing answers to the questions below were the webcast presenters, Alan McFarland, Panduit professional services solutions architect, and James Neawedde, Jr., Panduit professional services industrial automation solutions architect.

Question: With the metal industry industrial network case study, was there anything unusual that governed network design?

Answer: In the case study, the customer’s original network infrastructure was insufficient to meet the DMZ (demilitarized zone: a protective buffer area) and corporate security mandates, particularly those pertaining to the process control network. The new mandates required a "greenfield" approach [new installation] applied to a brownfield [existing or retrofit] environment. Planning for a number of undetermined future expansion needs required additional fiber capacity and bandwidth.

Question: How might safety integrity level 2 (SIL2) and SIL3 requirements figure into industrial network design?

Answer: In general, the recent updates to the safety standards such as IEC 61508 allow safety systems and devices (using CIP Safety*) to coexist and interoperate with standard plant floor devices on the same CIP network, such as EtherNet/IP. So, it is feasible to have CIP safety sensors operating alongside variable frequency drives (VFDs), safety, and standard controllers-while using standard Ethernet and IP network switching infrastructure. However, Panduit network designs do not address the logical design aspects of either control or safety systems, nor do we currently perform risk assessments, failure analysis, etc., that are involved with determining a systems SIL. [*The ODVA organization offers CIP Safety as a component to its industrial network family, which includes the EtherNet/IP industrial Ethernet protocol.]

Question: When starting with a network design, what generally is the sequence of considerations or questions during an assessment? Does it matter? (See slide 14 in the presentation.)

Answer: The exact sequence of questions during an assessment is not as important as making sure that all the stakeholders’ needs and requirements are captured and that confidence is imbued. Furthermore, it is critical that all parties reach a common understanding of the customer’s needs and expectations; this often necessitates multiple iterations of the requirements document.

Question: Can you give an example of how catching a design issue early saved money and the resulting cost savings?

Answer: An example of catching a design issue early, resulting in customer cost savings, follows. A customer who is building out a small section of the facility might develop a plan to meet only the minimum cabling and capacity requirements for that specific area. Given this scenario, a holistic approach that examines the entire facility may determine that the location being built out is in fact a prime aggregation area, which will require different cabling density or patching, etc. By identifying the prime aggregation locations early in the design phase, it is more cost effective to "upsize" the cable and include extra strand counts for future use, as opposed to adding additional capacity later.

Question: Do standards for network ever conflict? If so, how do you resolve the conflict? Do you have any examples to offer?

Answer: There are some differences among applicable standards. It is important for a designer to know which standards apply to a specific situation and which do not. Many times there are multiple approaches that meet the standards, but may not be ideal for service-ability and long term extensibility. These are two of the many considerations that can be used for resolving design conflicts. A comprehensive understanding of the appropriate standards applicable in a given situation is critical when developing the optimal solution. Recommendations may include such variables as physical media type and product set, etc.

Question: Do network design considerations vary by industry? If so, how? (Or are they more application-need dependent?)

Answer: Applications and networking needs can vary across industries. However, when migrating to Ethernet there are some common practices that should be followed regardless of industry. Some of these common practices include some common building blocks, tools, reference architectures, etc., that can be leveraged in almost all industries [as mentioned in the webcast resource slide during the Q&A].

Question: Do you have an example of operations versus IT language translation challenges or differences?

Answer: IT is less inclined to understand the environmental considerations in a manufacturing plant than operations. Operations is less inclined to understand network performance characteristics or the advantages of a structured cabling approach when migrating to an Ethernet platform. IT and operations tend to have different nomenclature. Some of the terms that can be confusing are IDF (intermediate distribution frame) versus zone enclosure, or TO (telecommunications outlet) versus industrial computer (human-machine interface [HMI] or man-machine interface [MMI]), programmable automation controller (PAC), or intelligent process devices. It is important to bridge these gaps and provide understanding to both parties. The networking requirements of an industrial automation and control system often differ from a typical IT network.

Question: What were the most important (or perhaps overlooked) aspects of network design as it related to the metals industry case study mentioned in the webcast?

Answer: The customer’s initial plans were not suitable for long-term sustainability and growth. Over time this ad-hoc approach would have required additional cable runs and increased maintenance costs. Providing an installation specification that was written in terminology clearly understood by most network cabling installers reduced the risk for ambiguity in the installation spec. As a result, this improved installation efficiency and quality.

Question: If the stop-gap measure described was used (just running fiber across existing connections), what would have been the limitations and when?

Answer: Had the stop-gap measure been employed in the case study, there would have been an increased cost for adding cabling as needed. Inevitably, more cable would have been required. More line loss would have been introduced. Network testing and certification would have been more challenging, tedious, and costly. The network switch deployment would have been less than optimal, creating a more fragile network, with potential for unbalanced network traffic, and performance issues with the production data display monitors and video surveillance. Performing moves, adds, and changes (MAC) would have been much more difficult, and the customer would not have reaped the benefits provided by a robust, highly available cabling infrastructure.

– Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering,


Register for and view the archived webcast and Q&A, with additional help with network design, including more details about the metals industry case study:

A Network Foundation — Applied Case Study in Deploying a Reliable Physical Infrastructure for Process. 

See a related article on these topics, based on webcast content.

Deploying a reliable physical infrastructure for process 

Author Bio: Mark Hoske has been Control Engineering editor/content manager since 1994 and in a leadership role since 1999, covering all major areas: control systems, networking and information systems, control equipment and energy, and system integration, everything that comprises or facilitates the control loop. He has been writing about technology since 1987, writing professionally since 1982, and has a Bachelor of Science in Journalism degree from UW-Madison.