What Are Permanent and Channel Link Tests?

Last modified: June 26, 2019
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Permanent Link Test

The tester main and remote have adapters with integrated cords of known performance. The device can, therefore, remove the loss of the cord from the total measurement, providing the performance of the link.

Patch Panel + Cable + Outlet (see diagram below):
Two Connector Permanent Link Test Diagram
Source: Fluke Networks

Why test an incomplete system without the cords?

By testing the permanent link, information is provided about the permanently fixed part of the cabling. A “pass” for this test ensures that the system is always functioning.

Channel Link Test

The main and remote testing units have adapters with RJ45 ports. These adapters connect to the cabling with standard patch cords. The test is, therefore, covering the complete channel

Cord + Patch Panel + Cable + Outlet + Cord (see diagram below):
Two Connector Channel Link Test Diagram
Source: Fluke Networks

This test has the advantage of covering the complete cabling between a switch and a computer, therefore ensuring that the application can function properly. However, the test is only valid as long as the patch cords remain in place. If one cord is replaced, then the test is no longer valid.

A good example of this would be when a device is not connecting to the network. Testing the channel can then give two answers:

Pass: The passive infrastructure is good, and the problem comes from the active devices.

Fail: Since the permanent link should have already been certified, this indicates that one or both of the patch cords are likely defective. In this case, a permanent link test should be repeated on the permanent cabling to confirm that the infrastructure has not been damaged or tampered with after it was last certified. Modular jacks with blank patch panels can replace patch panel for Permanent Link and Channel testings.  This set up is very common in data center environment.  Data modules in RESI enclosures can also replace patch panel in a residential environment for Permanent Link and Channel testings.

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