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I recently got a job in IT infrastructure and terminating Cat5e is something relatively new to me.

What is an acceptable bit error rate for 1 million packets?

Here is a screenshot of a test I conducted on a cable i terminated with Metal connectors. The cable was about 200ft. The test was done using Pockethernet. The cable was designed to transfer data from a Ubiquiti radio Dish down to a firewall inside an IT equipment room in the building. enter image description here

The reason I ask is because Google returns 10 to the power of 9 which is a large number and I don't know how it translates to this test.

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    If you are doing cable installation, you really need a tester (expensive) that can certify the cable by running the test suite (see this answer for the required basic tests) for the particular cable category. Simply identifying so many errors simply tells you there is a problem, but it does nothing to explain what the problem is. The cable tester will record all the tests for each cable run, and you can print a report. You need to resolve any problems with any of the tests before the cable can be certified.
    – Ron Maupin ♦
    Apr 25, 2020 at 1:02
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    We also don't know if that "error" is per bit, byte, or packet. In any case, out of 1mil full frames, there should be around 2 errored bits to meet the 1E-10 BER. You clearly have problems that your simple pocket tester will not even begin to answer.
    – Ricky
    Apr 25, 2020 at 3:34
  • Ok. it looks like im clearly not being given the proper tools for the job. Not sure if my company would be willing to spend the money on those expensive testers.
    – IzzM
    Apr 25, 2020 at 6:25
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin ♦
    Dec 17, 2020 at 17:03

4 Answers 4

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Most modern Ethernet variants are designed for a bit error ratio (BER) of 10-12 or better. Early variants only had 10-10 or better, see IEEE 802.3 for details.

In term of packets/frames, it depends on their average size. A maximum sized, untagged Ethernet frame requires 1526 bytes or 12,208 bits on the wire, so a BER of 10-12 roughly translates to a frame error ratio of 1.2×10-7. That's worst case, within specs - with decent, not maxed-out cabling, you're usually quite a bit better, like 10-9 or so. The 4.83×10-3 frame error rate you've measured is very high - depending on the exact purpose of that cable you'd have to decide whether you can live with it or not.

However: if you fabricate your own cables you need to use a tester than can certify the cable ($1000+). Effectively, that Pockethernet tester of yours can only measure the error rate for a certain protocol. It doesn't measure attenuation over the frequency range, the crosstalk varieties or the various other parameters.

It's not enough to try-and-error because you might want to run other protocols on your cables later on - a Cat-5e DIY cable that's running 1000BASE-T fine might give up on 2.5GBASE-T since that uses a larger frequency envelope. Certified cables are guaranteed to work in all specified scenarios.

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The Pocketethernet device counts the number of 1518byte packets with errors by checking the packet for CRC errors. Packets with errors are because one or more bits are altered and this measurement is the packet error ratio PER. This device technically can't measure true BER as number of bit errors per total bits because it only counts packets - it's still great for detecting errors.

To convert percent to scientific notation: 0.483% = 0.00483 = 4.83 × 10-3 which is between 10-3 and 10-4 (a calculator in scientific mode can convert and show you scientific notation).

If we assume you have a single bit error (best case) per packet, you have 4830 bit errors / (1000000 packets x 1518bytes x 8bits) = 3.16x10-7. This is should be rounded up to 10-7 BER and there's definitely an issue on your cable.

Try testing a few more cables of varying lengths to get a feel for the tester.

The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. Bit error ratio is a unitless performance measure, often expressed as a percentage. https://en.wikipedia.org/wiki/Bit_error_rate.

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  • 4.83 × 10^-3 is between 10^-2 and 10^-3...
    – Zac67 ♦
    Mar 6 at 10:56
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Pockethernet should be zero. I had one defective unit and I contacted the company and they replaced it. Also make sure you’re on the latest firmware of 33 (as of early 2021) because there was a software issue in previous versions that gave a false BER test result.

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BER contributes to Packet Loss, but they cannot be converted one to another. In principle, BER is hardware, PL is protocol. You can have BER 10E-12, and still 30% PL due to e.g., network congestion.

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  • Absolutely - however, the OP asked about BER at the frame level (see screenshot), just physical layer.
    – Zac67 ♦
    May 22 at 9:30

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