In January, our experts presented Bit Error Rate Testing (BERT) at the Building Industry Consulting Service International (BICSI) Winter Conference and Exhibition 2022. BERT is a powerful testing method that proves your Ethernet network will perform for your application in its installed environment. Some important points from the presentation include the following:
- Ethernet cable certification testing and BERT testing are both suitable for your most critical networking applications.
- Certification testing checks cable specifications and is usually required by the project scope or required for cable warranty purposes.
- BERT directly tests cable performance by taking the cable for a test drive, making it the easiest and most direct way to prove the cable will meet application demands in a given environment.
- Whereas certification testing provides an instantaneous measurement of cable specifications, you can use BERT to troubleshoot or prove cable performance — over a specific time period or continuously — to check for bit errors while nearby machines are moving, stopping or starting.
- Certification testing requires high-end expensive testers and trained technicians.
- Compared to certification testing, BERT uses lower-cost testers that are easy enough to be used by anyone.
Let’s break down some of these points in more detail.
Why is BERT Important?
BERT is a data test that checks the throughput capabilities of your cable to ensure the network will perform to your application needs. It is very different from certification testing in that it sends real bits of data down the cable and then counts errors at the other end of the cable. For these reasons, BERT is a real-world test, using and sending data across a cable in the actual environment where the cable will be installed.
How Does BERT Work?
For a field BERT test, one tester sends real data Ethernet packets down the cable from one side to the other. Each packet has a checksum to indicate if all the bits arrive. The checksum is verified at the other end, and if the checksum returns zero, then all the bits have arrived. This process must also be done in reverse — from remote to the local end. If both directions have zero errors, then BERT passes.
Since BERT simply involves sending data packets through sending and receiving endpoints of the network and checking for errors, it’s an easy process to understand — whether you’re a trained technician or a less experienced customer. As an example, send 10 Gigabits per second (Gbps) of data down the cable and count the errors in the data. Then, send the data in the reverse direction and count the errors. If no errors are found, then the cable is good to go for 10 Gbps.
When Should BERT Be Performed?
Since BERT depends on successful end-to-end data transfers, it is most useful after the initial installation and certification of cables — that is, after computers, printers and cameras have been installed, for example. And, it doesn’t matter what kind of passive device is used within the network. Although cable quality and type can affect the performance of the link, BERT doesn’t care what’s in the middle; it only cares about sending bits and having zero errors. As long as the data arrives, it doesn’t matter if the device is supported by CAT 6A, CAT 5 or fiber optic cables.
BERT is the perfect tool for projects like system integrations, upgrades or additions. Its simplicity ensures that anyone can pick up a BERT field tester, connect each cable end to the tester, start the test and wait for the results.
How Does BERT Differ From Certification Testing?
Cable certification testing does not check data. Instead, it tests cable specifications to ensure they meet Telecommunications Industry Association (TIA) global standards. If the cable specifications pass, then the cable should theoretically be good to go for its intended application. The scope of a network installation often specifies if certification testing is required. It may also be required due to building codes or for warranty purposes. Here’s an overview of some of the characteristics of certification testing:
- Testing protects cable manufacturers, as they’re providing a warranty for your installation. This warranty stops with the cable. In other words, cable manufacturers aren’t concerned with the application once you connect devices to the cables or install machines around them.
- Certification testing doesn’t send data bits down the cable, and certification can’t be used continuously or for long durations to watch the effects of other machines or the environment on the cable.
- Certification testing requires the most expensive testers, the most training and the greatest understanding of test setup and configuration.
- Certification testing is perfect for new cable installations in new buildings in critical applications. It can be required by the project scope, or when the cable manufacturer is providing a cable warranty after installation.
On the other hand, BERT doesn’t test the cable specifications. Rather, it moves data bits across your cables and tests them for bit errors according to IEEE 802.3 standards, enabling you to prove the cable — and the entire link — is fit for your application. Unlike certification testing, BERT can be used continuously for long durations to prove the cable will perform in its environment without bit errors as machines are running, stopping and starting, as cables are swinging and other environmental effects. And, performing BERT is easy, requires almost no training and is much less expensive than certification testing.
BERT testing is ideal for critical applications that look more like systems integration projects, where you have cables, network devices, active machines and people, and you want to prove the cable will perform for your application in its installed environment.
What’s an Example of a BERT Application?
If certification testing isn’t required, then BERT is a powerful, yet simple way to prove cable performance. For example, imagine you have to upgrade a carwash with 4K video monitors. With BERT, you can test the cables and see if they’ll perform at 10 gigabytes per second (Gb/sec). You can also set the tester to run in continuous mode, testing BERT for the entire duration of the carwash cycle to prove there are no bit errors due to nearby machines starting, stopping or moving. If the cables pass, then your 4K cameras will have plenty of bandwidth to operate.
Compare this example to certification testing. Imagine again you need to tell the carwash owner you’re about to perform a cable test according to CAT 6A cable standards, running a frequency sweep across a frequency spectrum to 2,000 megahertz according to TIA global standards. If the test is a success, then the cable specifications should be able to support 10 Gbits/sec data rates. This testing method takes much more technical expertise to perform and understand, and it only tests one snapshot in time — not the full duration of the carwash cycle.
In this carwash example, an easier conversation with the carwash owner would look something like this: “I’m going to run a 10 Gbit/sec BERT test — or data rate test — on your cable, while the carwash runs its cycle. If I get no bit errors, then the data is arriving at the speed we need for video performance throughout the cycle of your carwash.”
What Are Some of the Benefits of BERT?
BERT offers many benefits. For example:
- It is easy to perform. BERT is like test driving a car. On the other hand, certification testing is like trying to see if the car will work for you by looking at its specifications.
- It is powerful. If there are no bit errors during the test, then your devices will work.
- It is direct. If you need 1 Gbit/sec of data for your application, then simply perform a 1 Gbit/sec BERT test. If the cable passes, then it is good to go for your application.
- It reveals environmental effects on cables. Testing a cable in its installed environment is a very powerful tool. For example, imagine the cable has been installed in a particular location for five years — all the while being bent, pulled or moved. Cable damage could result in bit errors, and BERT lets you find these.
Where Can I Learn More About BERT?
To explore BERT in greater detail, check out the following videos:
- Watch our experts use BERT to detect electromagnetic interference on Ethernet cables.
- Watch our experts run BERT tests on a fiber optic cable to 10 Gbits/sec.
- Watch our experts compare BERT and certification testing on a copper Ethernet cable.