Industrial Ethernet: managed or unmanaged switches?

Just because you can use an unmanaged switch does not mean you should use an unmanaged switch. It has been said that you will either use a managed switch or wish you had, explains Carl Henning, deputy director, PTO, Profibus and Profinet North America. See related links.

04/17/2009



PTO offers specifications, profiles, guidelines, installation information, brochures, technical write-ups, white papers, and more.

Just because you can use an unmanaged switch does not mean you should use an unmanaged switch. It has been said that you’ll either use a managed switch or wish you had, explains Carl Henning, deputy director, PTO, Profibus and Profinet North America .
Here are additional Henning Ethernet observations:

  • The logic is that an unmanaged switch has diagnostic information consisting of blinking LEDs. If your line goes down due to a switch failure and you can tolerate the downtime to go find blinking lights, an unmanaged switch might be the right choice for you.

  • If you can’t stand the downtime, then use a managed switch. Its onboard diagnostics can be read by many kinds of software from the IT world.

  • Use an SNMP (Simple Network Management Protocol) OPC Server to move diagnostic data from the switch to an HMI. Managed switches maintain a database of important switch activity.

  • The database is called an MIB (Management Information Base). For example, numerous retries on a particular switch port might indicate a network problem. Alerting maintenance through the HMI could prevent an unplanned shut down.

  • Of the three most popular Industrial Ethernet protocols, Profinet and Modbus/TCP can use either managed or unmanaged Ethernet switches; Ethernet/IP requires the use of a managed switch. Ethernet/IP needs a managed switch because it requires the IGMP (Internet Group Management Protocol) Snooping function which is not available in unmanaged switches. Ethernet/IP uses broadcasts to transmit IO data. To prevent this from overloading the network, IGMP Snooping learns where broadcasts messages are going and restricts them to only the interested nodes. This prevents the network from being overloaded with traffic.

  • Some Ethernet switches can also act as IO devices. For example, a switch that uses Profinet to access the MIB can move diagnostic data to a controller in addition to an HMI. The controller could then react and respond to the condition rather than just creating a notification on an HMI screen.

  • This ability to use information that is already there overcomes one of the major concerns of control engineers and maintenance staff: “How can I diagnose and fix network problems? Do I need special equipment? My maintenance staff doesn’t carry laptops.” Downtime can be minimized by bringing this information into systems that automation folks are already familiar with (HMIs and PLCs) and are already installed.

Also see:
-

Industrial Ethernet: Environmental conditions determine hardware selection

;
- A related white paper that helps with some of those decisions while pointing out differences between Ethernet for IT and automation domains (PDF) ; and
-

Plug into Industrial Ethernet Protocols

: Industrial Ethernet protocols can be standard and unmodified, or modified to be industrially hardened. Perspectives from some protocol proponents clarify needs for various implementations.
www.us.profinet.com
- Edited by Mark T. Hoske , editor in chief
Control Engineering News Desk
Register here to select your choice of free eNewsletters .





No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
Each year, a panel of Control Engineering editors and industry expert judges select the System Integrator of the Year Award winners.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Learn how to create value with re-use; gain productivity with lean automation and connectivity, and optimize panel design and construction.
Go deep: Automation tackles offshore oil challenges; Ethernet advice; Wireless robotics; Product exclusives; Digital edition exclusives
Lost in the gray scale? How to get effective HMIs; Best practices: Integrate old and new wireless systems; Smart software, networks; Service provider certifications
Fixing PID: Part 2: Tweaking controller strategy; Machine safety networks; Salary survey and career advice; Smart I/O architecture; Product exclusives
The Ask Control Engineering blog covers all aspects of automation, including motors, drives, sensors, motion control, machine control, and embedded systems.
Look at the basics of industrial wireless technologies, wireless concepts, wireless standards, and wireless best practices with Daniel E. Capano of Diversified Technical Services Inc.
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
This is a blog from the trenches – written by engineers who are implementing and upgrading control systems every day across every industry.
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Control Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.