Critical Skills for Novice Network Engineers: Go beyond CCNA theory and learn the practical day-to-day skills you need as you start your networking career. by Andy Kelsall

Author:Andy Kelsall [Kelsall, Andy]
Language: eng
Format: azw3, epub
Publisher: Andy Kelsall
Published: 2020-06-18T16:00:00+00:00

A problem with the service provider’s network (meaning Networks-R-Us network).

A defective router interface.

A cable has become unplugged

Troubleshooting the Circuit

You now know for certain that you have a layer 1 issue. What is your next step? Access a test point within your company’s network and begin troubleshooting. A test point allows you to remotely “break into” a circuit and isolate where the problem is located. You isolate the problem by seeing where you have lost continuity on the circuit by checking to see if you can send and receive a test pattern to a smartjack loop, a CSU loop, or by testing “head-to-head” with a field tech. You will typically use a GUI (Graphical User Interface) to access a test point, and for any given circuit, you will have at least one test point.

The two scenarios outlined below will help explain the troubleshooting process in more detail. As you read each scenario (and when you are on the job), always be aware of the direction you are testing towards (meaning, are you testing towards the CE router or the PE router?). If you fail to notice which direction you are testing towards, you could easily end up wasting valuable time trying to a fix a problem that isn’t there. For example, let’s say you cannot loop up the smartjack, and you “think” you are testing towards the CE router (but in reality, you were testing towards the PE router). You proceed to open up a ticket with the LEC on the CE side, when you should have opened a ticket up with the LEC on the PE side. You have just wasted not only your time and the LECs time, but more importantly, you have also extended the customer’s outage.

As you read through the upcoming scenarios, refer to the simplified network diagrams below. In the second diagram, the shaded area represents the circuit itself. You will always have a least one test point that allows you to break into a circuit and perform testing. Here, I show two test points (TP1 and TP2). If a circuit doesn’t pass through a test point, you have no way to remotely break into the circuit and test it.

When we access a test point and open up a circuit, that’s known as “splitting the circuit.” Once you have split the circuit, you can test in either direction and isolate where the problem is on a circuit. As shown by the green dashed lines, you can test in both directions from TP1. You can do the same from TP2 (although I only show testing in one direction from TP2). Also note that you can loop up the smartjack and CSU from either test point.

Note: The green and red dashed lines represent the direction of the test signal as well as which device can be looped up for testing.

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