Network diagnostic tools aided by intelligent design, maintenance

Network diagnostics is really one of three phases involved in successful deployment of industrial networks. The first phase is proper design and installation, including appropriate diagnostic capabilities. The second is network operations, which includes periodic check-ups and proactive maintenance to ensure network health.

12/01/2002


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SIDEBAR: Balance alleviates network demons

Network diagnostics is really one of three phases involved in successful deployment of industrial networks. The first phase is proper design and installation, including appropriate diagnostic capabilities. The second is network operations, which includes periodic check-ups and proactive maintenance to ensure network health. The third phase is post-failure repair, which is when most traditional diagnostics are performed.

Maintenance and post-failure diagnostic tools include handheld meters, in-line devices, laptop PC-based components, monitoring software and other more application-specific accessories.

Handhelds, other tools

Though they appear to have evolved from traditional voltmeters and multi-meters, handheld network diagnostic tools have more in common with advanced test equipment. They still gather electrical signals, but, rather than requiring an operator to interpret a signal based on experience, these newer devices extract key voltage measurements from the complex network activity. This advanced capability is often accomplished by combining a protocol analyzer and an electrical signal analyzer in one handheld tool.

The IT world has its own array of specialized tools. Network sniffers are devices that are permanently connected to networks to monitor them and provide diagnostic data. They too monitor a network's wires; examine the protocols that are running; and help determine if the network is healthy.

Another tool familiar to IT professionals is the time domain reflectometer (TDR). TDRs send pulses over network media and measuring media and measure reflections to pinpoint any problems, such as shorts, opens, mis-wired connectors, excessive cable lengths or incorrect cable types. It is very common requirement for new Ethernet media installations to be 100% tested and certified by the installer using a TDR. Media testers are also available for industrial control networks and have significant value when used during installation to verify correct installation. The downside is that active testers such as these must be used on an inactive network, often with nodes disconnected.

Besides the usual handheld devices, network diagnostics can also be done with PCs and laptop computers combined with network interface cards (NICs) featuring built-in diagnostic capabilities and related software.

Because different diagnostic tools measure different phenomena, engineers often have to use more than one. For example, using a TDR on cables before powering up can help confirm the physical layer. Next, protocol and electrical analyzers can check the network's electrical characteristics and performance, which includes network error rates and bandwidth utilization.


Author Information

Nick Jones, staff researcher, Woodhead Connectivity (Waterloo, Ontario, Canada) and chief technical officer,


Balance alleviates network demons

Networks specifications generally strike a balance among several competing requirements, including data rate, distance and noise immunity. Improving one characteristic of a network often results in degradation of another.

Other network features, such as media access method-deciding who gets to talk next on shared media-and integrated power supply in the cable, can have side effects. These also have to be considered when defining physical-layer specifications and guidelines.

Proper installation strikes the right balance in a network deployment to combat potentially demonic problems from hampering network performance. These include:

Bus errors, often intermittent and usually caused by physical- layer problems, can be tracked down using diagnostic tools to check error rates for each node.

Marginal media, also includes a range of obvious and subtle problems, such as loose, corroded or improperly installed connections or cables; faulty device circuitry; and topology-related problems.

Noise, or signal interference caused by external influences, which are either electric, electromagnetic or magnetic.

Source: Control Engineering with data from 'DeviceNet Physical Layer: An Insider's View' and 'Three Hidden Demons in Your Network' by Nick Jones, staff researcher, Woodhead Connectivity (Waterloo, Ontario, Canada), and available at and



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