Webcast questions and answers on reliable fiber optic networks: design and deployment best practices

Fiber optic network tutorial: Questions and answers follow about how to avoid electromagnetic interference (EMI) and achieve longer distances and higher performance using fiber optics for EtherNet/IP networks across manufacturing zones and devices. Panduit Corp. answers audience questions from an archived webcast on physical layer best practices and understanding proper fiber media selection for each physical layer in the EtherNet/IP network, along with design recommendations.


Additional answers are provided below about how to avoid electromagnetic interference (EMI) and achieve longer distances and higher performance using fiber optics for EtherNet/IP networks across manufacturing zones and devices. Robert Elliot, business development manager, Panduit Corp., answers audience questions from an archived April webcast that provides instruction regarding physical layer best practices and understanding of proper fiber media selection for each physical layer in the EtherNet/IP network, along with design recommendations.

Answers provided below offer a fiber optic communications tutorial in response to additional audience questions that wouldn't fit into the scheduled one-hour timeframe for the webcast. The webcast, which originally aired Thursday, April 23, 2015, is available for viewing after registration. Please link to the webcast at the bottom of this file.

Q1: How do you enforce separation between information technology (IT) and manufacturing networks?

A: IT and manufacturing networks need to be separated by an effective firewall system. This is outlined in the Cisco — Rockwell Automation "Converged Plantwide Ethernet Design and Implementation Guide": 

Q2: What cabling issues are you seeing with 100 Mbps Ethernet over fiber/copper?

A: One of the issues we're seeing with 100 Mbps Ethernet over fiber and copper is right in the automation island, where the prevailing practice is to field terminate with copper cabling and not measure the performance of the permanent link. At lower data rates, this practice may not reveal any type of problem. As data rates increase, any performance shortfalls will show up in the loss of data integrity.

Q3: What are some ways that safety and security can be addressed?

A: Use of virtual local area networks (VLANs) to segment network traffic and the use of an effective firewall system as outlined in the Cisco — Rockwell Automation "Converged Plantwide Ethernet Design and Implementation Guide" provide a very secure operating network. Additional physical security components such as jack block-outs, keyed connectivity, and plug lockins deter accidental insertion or removal of connectivity components.

Q4: 1) What is the best way to manage conducting components of fiber cables to avoid EMI and grounding issues, such as metallic shields, armor, tracer wires, etc.? 2) What are recommendations for depth of burial (land location issues) to avoid excavation damage, particularly in service areas?

A: Conventional armored fiber usually uses a flexible metallic external sheath to provide protection. This metallic armoring has to be effectively grounded at both ends of the cable run. One issue we have seen is that in brown field sites, the utility feed may not be from the same point, so there may be a significant potential difference, such as greater than 1 V RMS [root mean square], between the two end points. In that case, the use of a potential equalizing conductor may be required to connect the two end points and eliminate the ground potential difference.

On the subject of burial depth, some guidance for North America is given in the BiCSi "Telecommunications Distribution Methods Manual" (TDMM) and also the National Electric Code, Article 300.5.

Q5: Please comment on installation practices, security, and future bandwidth.

MICE criteria (Mechanical, Ingress, Climatic/Chemical, and Electromagnetic), which are categories of environmental conditions from the Telecommunications Industry Association (TIA), can enhance industrial network reliability when appropriately applied. CoA: With respect to installation practices, Panduit would recommend starting with a standards-based network design, such as TIA-568 and TIA-1005 standards for North America and then using best practice installation methods described in BiCSi standards, such as the "Telecommunications Distribution Methods Manual" (TDMM) from BiCSi. Security is achieved by means of a combination of approaches, logical (such as VLAN, firewalls) and physical (such as keyed connectivity, lockable enclosures, etc.).

Use of standards-based approaches for the design and installation of network cabling will focus on the use of the permanent link which is tested after installation. This provides assurance that present day and future performance requirements are met, thereby accommodating future network data needs.

Q6: What are the best practices to ensure 100% reliability and 100% on-stream time?

A: Best practices to achieve high reliability are described in the Cisco — Rockwell Automation "Converged Plantwide Ethernet Design and Implementation Guide." In addition, use of a fiber-ring topology using Resilient Ethernet Protocol (REP) is recommended for high availability networks.

On the physical layer side, some of the key steps to be followed are summarized from the webinar: 1) Adopt converged plantwide Ethernet topology; 2) Use standards-based designs; 3) Use zone topology; 4) Identify target uses for optical fiber, select the right fiber, and know the equipment and network you're connecting to the distance requirements, as well as bandwidth and fiber counts; 5) Understand the application environment, using MICE criteria [See table on Mechanical, Ingress, Climatic/Chemical, and Electromagnetic conditions in webcast]; and 6) Measure the permanent link performance.

Q7: With fiber optic networks, how do you test for reliability during commissioning?

A: A standards-based design approach focuses on the use of a testable permanent link as part of the overall channel. Validation of the link performance through testing ensures reliable data throughput. Additional fiber installation and handling best practices are given at: http://www.flukenetworks.com/content/fiber-testing-best-practices-pocket-guide-google

Q8. Can fiber optics that are used for communications also be used for lighting?

A: No, this is a safety hazard. Optical fiber used for communications cannot be used to provide lighting. Wavelengths of the signals used in optical fiber transmission of Ethernet described in the webinar lie in the infrared part of the spectrum and are not visible. IMPORTANT SAFETY HAZARD: A user of an energized optical fiber must never look into an exposed end of the fiber for risk of serious eye injury.

Q9: What's the cost of fiber optic communications versus wireless?

A: This is a tough question to answer, because it really depends upon what you want the media to do. Optical fiber will offer the ability to support high data rate traffic, over distances of hundreds of meters (multimode) to tens of kilometers (single-mode) in a secure way. A wireless deployment will offer the ability to support mobile users and can be used in areas where access for installation of cable is not easy. The wireless deployment, depending on type used, may be capable of being powered by Power over Ethernet (PoE) so that a utility power source is not required.

Q10: What's the future of EtherNet/IP?

A: One point we're pretty sure of is that with time, data rates will rise. Fiber cabling and connectivity are specified in the EtherNet/IP Ethernet protocol standard from ODVA for up to 1 Gigabit per second (Gbps), but as yet there is little discussion for 10 Gbps. On the other hand, copper channels are only specified for 10 / 100 Mbps and it is expected that will rise to 1 Gbps in the future.

Q11: What are the types of fiber?

A: The key choice facing designers is whether to use multimode or single-mode fiber. The choice can be summarized as follows:

Multimode fiber — consider for use over distances of up to 550 meters at 1 Gbps or 2 km at 100 Mbps, uses lower cost transceivers, connectors, and installation.

Single-mode fiber — consider for use for longer distances of up to 40 kilometers, high bandwidth requirements, and uses high cost transceivers.

Occasionally, reference will be made to Plastic Optical Fiber (POF). This type of fiber is very easy to install and involves the use of a much larger diameter polymer fiber. It supports low data rates, and the maximum reach of the POF channel is only a few tens of meters and so is not widely used for Ethernet applications.

Q12: Which are the best fiber cables? What is the next step for fiber optics?

A: The choice for optimum fiber types is given in the response to question 11, above. In terms of what's next, I think there are two areas where we see for the use of optical fiber in the industrial environment. The first is for use of dielectric conduited fiber (DCF), where a rugged crush-resistant polymer conduit surrounds the optical fiber, offering an alternative to armored fiber that is lighter, more compact, and does not require attention of grounding and bonding. The second is for use of polymer clad fiber (PCF), where the glass core and cladding is of a larger diameter than used in single-mode or multimode fiber, offering a very electrician-type, installer-friendly means for termination.

Q13: Please compare fiber optic connector types and benefits of each.

A: There are many fiber connector types in existence, maybe as many as 20 or so, though many of these are no longer in use. With time, we're seeing a focus on the use of the Lucent Connector (LC), which offers a very small form factor useful for high density applications seen mainly in data centers. We're seeing industrial automation network switch manufacturers also focus on this connector type. This connector snaps into the mating adapter. We see the Square, or Subscriber, Connector (SC), which also has a snap coupling, and the Straight Tip Connector (ST), which has a bayonet style coupling for use closer to the node or end point.

Q14: How should network redundancy be used for critical applications like process industries?

A: The Cisco — Rockwell Automation "Converged Plantwide Ethernet Design and Implementation Guide" describes design principles used to assure highest network reliability. Networking topologies, such as Resilient Ethernet Protocol (REP) and the use of a fiber-ring approach to connect Layer 2 switching, give a rapidly convergent redundant networking approach. Closer to the node, Device Level Ring (DLR) can be used with a fiber or copper ring architecture. In more traditional star networks we have seen the use of dual uplinks from network switches (main and redundant). In some cases these cables are routed on physically separated pathways.

Robert Elliot, business development manager, Panduit Corp., answers audience questions from an archived April webcast, “Reliable Fiber Optic Networks: Design and Deployment Best Practices.” Courtesy: Panduit Corp.Q15: After installation, what are the types of test methods, the most common installation errors, and the most common design errors?

A: Key to the testing performed is the measurement of the performance of the permanent link. This qualification involves the use of a light source at one end and receiving equipment at the other end of the link. The equipment will validate against TIA-568-C.3 performance limits. The equipment will guide troubleshooting and identifies connectors with high loss as well as high reflectance. Single-mode installations are more difficult to carry out because of the smaller core diameter. These systems also are not tolerant of poor reflectance. The key design step is to ensure that the power loss budget calculation described in the webinar is carried out.

- Robert Elliot is business development manager, Panduit Corp.; edited by Mark T. Hoske, content manager, Control Engineering, mhoske@cfemedia.com

ONLINE extra

View the related webcast - A PDF of the slides is available for download.

Panduit Corp. "Reliable Fiber Optic Networks: Design and Deployment Best Practices." 

Cisco — Rockwell Automation. "Converged Plantwide Ethernet Design and Implementation Guide." Updated September 9, 2011. 

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