External Noise on Cabling Links

External Noise on Cabling Links
Question
========
I have tested my cabling system with a cable tester. The cable tester detected 'external noise' on some links. Are there any limits in the industry standards concerning external noise? What can be done in this situation?


Answer
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Unfortunately, there are no limits in the cabling industry standards
(TIA-568A) concerning external noise. So it is not possible to run some sort
of Autotest on cabling links that will tell if the external noise is
within or out of standard limits.

The simplest solution would be to find possible interference sources and
provide more spatial separation between them and cabling links.

One of other solutions is to try to run 'application compliancy' tests.
Application compliancy test is a test that will tell if the cabling links comply to the requirements of appropriate network protocols (10Base-T, 100Base-T etc.). This functionality is available in good cable testers (eg, Microtest Omniscanner).

The procedure looks similar to the testing for Category 5 compliancy. You plug the tester into the cabling system and select something like 'IEEE test'.

The third solution is to use a protocol analyzer (eg, software-based
Linkview http://www.linkview.com) and to check if actual bit error rate on your noisy cabling links exceeds the maximum allowed bit error rates for appropriate network applications.

If these tests are OK, then your network is OK. There may be some noise on
the links, but it is within aplications limits and is tolerated by active
devices.

If these tests are not OK, then you may try the following actions:

- increase physical separation between cabling links and interference sources.
- put noisy lines into fully enclosed, grounded metal conduit or raceway or install cabling links close to a grounded metallic surface.
- use fiber optics instead of copper cables.

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