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Exam N10-008 topic 1 question 13 discussion

Actual exam question from CompTIA's N10-008

Question #: 13
Topic #: 1

A technician is installing a new fiber connection to a network device in a datacenter. The connection from the device to the switch also traverses a patch panel connection. The chain of connections is in the following order:
✑ Device
✑ LC/LC patch cable
✑ Patch panel
✑ Cross-connect fiber cable
✑ Patch panel
✑ LC/LC patch cable
✑ Switch
The connection is not working. The technician has changed both patch cables with known working patch cables. The device had been tested and was working properly before being installed. Which of the following is the MOST likely cause of the issue?

A. TX/RX is reversed
B. An incorrect cable was used
C. The device failed during installation
D. Attenuation is occurring

Show Suggested Answer

Suggested Answer: A 🗳️

by geober at Jan. 20, 2022, 5:34 p.m.

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Lu5ck

Highly Voted 3 years, 4 months ago

Selected Answer: A

It is a fiber network and fiber has insane range thus it is unlikely to be attenuation. Bad device and bad cable are out because they are explicitly tested as described. Therefore TX/RX is the only reasonable option.

upvoted 21 times

StrawberryTechie

1 year, 11 months ago

it says incorrect cable, not bad cable

upvoted 2 times

8choxo

1 year, 8 months ago

Potato Potatoe

upvoted 10 times

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rodwave

Highly Voted 10 months, 2 weeks ago

Selected Answer: A

Going with A. TX/RX is reversed since it makes the sense to me given the other options: If the TX (transmit) and RX (receive) fibers are reversed in either of the LC/LC patch cables or the cross-connect fiber cable, the data will not be transmitted and received correctly, resulting in a connection failure. Also, I think the question listed the order of the connections and multiple patch panels to suggest that there was good chance of some kind of misalignment going on when the fibers were installed. --------- B. An incorrect cable was used: The question mentions that both patch cables were changed with known working cables, so I doubt that the cables are the issue here or that they would grab the same incorrect cable C. The device failed during installation: They mentioned that the device was tested before installation, so it probably didn't fail during installation either. D. Attenuation is occurring: Attenuation is the loss of signal strength as it travels through a medium. This could make sense if this was over a long distance, but it's a datacenter so the connections are made over a short distance.

upvoted 5 times

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Mehsotopes

Most Recent 10 months, 2 weeks ago

Selected Answer: A

Most fiber connections consist of two individual cables, one for transmission of data & one for receiving data. If you're connecting a switch to a workstation using a NIC that has Straight Tip (ST) connections on it, one will be Tx, & one will be Rx. You can check the NIC the ST connections are attached to, the solid orange light will indicates a good idle connection & blinking indicates the network is actively communicating through connection.

upvoted 1 times

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JakeCharles

2 years, 6 months ago

Selected Answer: A

I would go for A

upvoted 2 times

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Z_186

2 years, 9 months ago

I have a hard time believing the answer is A. An LC cable has both the TX/RX in place with one connector, it's not like an ST where the cables could be swapped. My best guess would be B then? Just because the cable is good doesn't mean it's compatible. Based on this from Meyers "Finally, different runs of fiber use different wavelength signals. You might be able to plug an LC connector into a switch just fine, for example, but if the signal starts at 1310 nm and the switch expects 1530 nm, that sort of wavelength mismatch will stop the transmission cold." Still not 100% sure though.

upvoted 3 times

CTE_Instructor

2 years, 7 months ago

LC fibers can be swapped because you can easily remove the connecting bracket.

upvoted 3 times

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Nate71290

2 years, 3 months ago

While they do have them "in place" with one connector sometimes from the factory/distributor they are crisscrossed...this has happened to me before on a job. Therefore, like CTE_Instructor mentioned you can easily remove the connecting bracket to roll the connections.

upvoted 2 times

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Kessel

2 years, 2 months ago

You mentioning the issue of wavelength signals is very interesting. However, let's remember that option B says "wrong cable", not wrong connector or wrong signal. Also even if a LC has a fixed TX/RX in place with one connector, you can still mess up with a mislabelled patch panel. I would still bet on A.

upvoted 2 times

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jr6666

3 years, 1 month ago

answer is a

upvoted 1 times

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Touch_91

3 years, 2 months ago

Answer is A

upvoted 1 times

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Stpn2me

3 years, 5 months ago

We have to understand the difference between crossover and straight through cabling..

upvoted 3 times

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itssnowyseason

3 years, 5 months ago

Answer is A?

upvoted 1 times

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geober

3 years, 6 months ago

Sorry that was not properly set up

upvoted 1 times

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geober

3 years, 6 months ago

Tx/ Rx are abbreviations for Transmit and Receive respectively so that was was properly set up

upvoted 3 times

ArchEpic

3 years, 5 months ago

Correct, but, TX/RX reverse means the ingress and egress traffic ends of, depending on the pinout configuration, and reversed or plainly wrong. Even though, no saying that, answer B also seems viable but answer A is more correct definition for the problem the technician is facing.

upvoted 3 times

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