Cable Troubleshooting

Question 1

What is throughput?

Answer 1

the amount of data transferred in a given timeframe.
How much water is flowing through the pipe.

Question 2

What is bandwidth?

Answer 2

that amount of data that can be transmitted (theoretical)
The size of the pipe

Question 3

What is attenuation?

Answer 3

The loss of signal strength.
expressed in decibels. (dB)

Question 4

What is interference?

Answer 4

Anything that gets transmitted within or close to the channel that isn’t the intended signal.
Expressed in signal to noise ratio. (SNR)

Question 5

What must you do when troubleshooting a permanent link?

Answer 5

Verify the cable type is appropriate to the application.
Verify unsheileded hasnt been installed where sheilded or screen would work better.
Using a incorrect cable.

Question 6

What does a cable tester do?

Answer 6

Reports detailed information on the physical and electrical properties of a cable.
Can be used for troubleshooting and verification.
Fully featured cable testers/certifiers are expensive.

Question 7

What can a wire map tester do?

Answer 7

Detects improper termination issues, identifies issues like:
Continuity- cant form a circuit cause of cable damage or improper wiring.
Open- a break in the wire
Short- two wires that are touching each other
Incorrect pin-out/incorrect termination/mismatched standards- conductors incorrectly wired into the terminals
-Reversed pair–pairs are wired to the the wrong terminals
-Crossed pair- pairs are wired to the wrong pins
-Split pairs- one wire going to the wrong port, causes cross talk

Question 8

What does a toner generator (or toner) do?

Answer 8

used to trace a cable from one end to the other so you can properly identify that same cable in a bundle or duct.

Question 9

What is interference from nearby data cables called?

Answer 9

alien crosstalk

Question 10

What does a visual fault locator do?

Answer 10

identifies the location of a break, excessive bend or improper splicing in a fiber cable by shining visible light down a cable.

Question 11

What happens if your optical cables are dirty?

Answer 11

The transmission path will be greatly reduced.
Normally occurs at a connector so cover them with dust caps when not in use.

Question 12

What is ORL?

Answer 12

Optical return loss
light that is reflected directly back down the cable toward the source.
Ultra Physical Contact (UPC) and Angled Physical Contact (APC) polishing reduce ORL reflections

Question 13

What steps are taken to troubleshoot cable issues?

Answer 13

1. Physical inspection
2. Reseat the cable
3. Verify Drivers

Question 14

What is a optical link budget?

Answer 14

The calculation of total loss in signal strength that occurs in all components in a fiber optic transmission path.

Question 15

What is Near End (NEXT) crosstalk?

Answer 15

Measures crosstalk on the receive pair at the TRANSMITTER end.
Usually caused by excessive untwisting of pairs, or faulty bonding of shielded elements.

Question 16

What is Attenuation to Crosstalk ratio, Near end (ACRN)?

Answer 16

Difference between insertion loss and NEXT
ACR is equivalent to SNR (signal to noise ratio)
high value = signal is stronger than noise
value closer to 0 = link is likely subject to high error rates.

Question 17

What is Attenuation to Crosstalk Ratio, Far End (ACRF)?

Answer 17

measured on the receive pairs at the RECIPIENT end.
the difference between insertion loss and FEXT= ACRF
measures cable performance regardless of the actual link length.

Question 18

What is power sum crosstalk?

Answer 18

Gigabit and 10 GbE Ethernet use all 4 pairs.
Power sum calculations confirm that a cable is suitable for this kind of application.
measured by energizing 3 of 4 pairs in turn.