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What is Excessive Read Rate, and How Do You Solve It?

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As part of our series on BACnet best practices, we’re highlighting some of the most common diagnostic issues you’re likely to encounter. This week, we’re focusing on a common BACnet issue, excessive read rate. Let’s look at what it is, why it’s not necessarily a bad thing, and how to identify misconfigured devices to keep your OT network traffic optimized.

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What is Read Rate?

Falling under the umbrella of “data polling” attributes, “BACnet excessive read rate” is the frequency at which a device on your network is requesting data from another device. In the case of, say, a temperature sensor, the read rate would be how often a device is polling that sensor to provide an updated measurement.

What Makes It Excessive?

While polling and reads are normal functions of your system, it’s not uncommon to have these requests become overwhelming. Think of our temperature sensor above. If that device is being constantly polled for updates, it’s generating data on the network, and consuming CPU cycles. Now assume you have hundreds of similar sensors all generating a constant stream of data across a network with limited bandwidth. The traffic adds up fast.

OptigoVM Diagnostic showing the results of a free scan, indicating excessive read rate errors
OptigoVM's diagnostic suite indicates excessive read rates. Free version results shown.

Excessive read rates can negatively affect the performance of your network, leading to an increase in response times, decreased resources, and instabilities across your system.

In OptigoVN, Excessive Read Rate warnings are displayed in the expanded list under Rate and Frequency of Object Reads, Writes, and COVs>Excessive Read Rate. Our diagnostic threshold returns a warning when a read property request for the same point occurs more than once within a five-minute span. 

Not all High Read Rates are “Excessive”

It’s important to note that high read rates aren’t always a bad thing. There are certainly situations where precise data is a requirement. Back to our temperature sensor. If that sensor is located in a highly sensitive area, like a data center where temperatures can rise 3.5 degrees for every minute the cooling system is offline, you may want frequent readings to maintain a very precise temperature. But a sensor monitoring the temperature outside the building? Those readings aren’t going to fluctuate often, so constantly polling for updates won’t provide more value.

In our experience, excessive read rates are often the result of programmers creating blanket polling policies for all object types across all devices. In a large system, this has the potential to trigger a flood of unnecessary data traffic.

How To Fix Excessive Read Rates

In this case, the “fix” is a simple matter of tuning the frequency of read rates to help optimize your overall network performance. OptigoVN’s Site Scopes can help you dig into your diagnostic test results to identify the culprit devices that are triggering a failed diagnostic result by exceeding our threshold.

OptigoVN’s Site Scopes show users a detailed view of devices returning an excessive read rate.
OptigoVN’s Site Scopes show users a detailed view of devices returning an excessive read rate.

We’ve also created a handy cheat sheet of Object reference descriptions to help you understand what value is being read. 

With this information, you can now tune your devices to a more appropriate polling rate if needed. Some common ways to consider tuning include: 

  • Configuration Review: Review and verify configuration settings for data polling rates to ensure they align with the intended requirements.
  • Reduce Poll Rates: Set appropriate polling frequencies based on the importance of the data, the rate of change, and the system’s operational needs.
  • Optimize Control Programming: Optimize control programs and scripts to avoid unnecessary or redundant data polling.
  • Convert Reads into Change-of-Value: Instead of polling the value, use a Change-of-Value “push” notification when the value changes.

Continuous Network Monitoring: Monitor network traffic and resource usage to identify patterns of excessive read rates.

Don’t Forget to Check Your Work!

Once you’ve completed your tuning, we recommend OptigoVN users upload new PCAP files (or set up continuous monitoring with our BACnet Capture Tool) to confirm improvements to your network health. 

Simply click back into the “Excessive Read Rate” results, search for a destination device, and confirm that the average gap between reads has increased, or disappeared, which means the average gap is now >300s.

Ready to help quiet the noise and bottlenecks BACnet excessive read rate can cause across your OT networks? OptigoVN offers free monitoring and diagnostic tools for your BAS and OT networks. Sign up for free today.

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