Troubleshooting cabling and interfaces 5.2

Question 1

Fiber mismatch

Answer 1

Use correct fiber cable type (multimode vs single mode) Should be written on outside

Question 2

Copper mismatch

Answer 2

May need to use one type vs another due to speed or distance reasons. Test cable with cable tester.

Question 3

Shielded vs unshielded twisted pair

Answer 3

Shielded can protect against interference but needs to be grounded. Unshielded can be cheaper and doesn’t need grounding but can have crosstalk

Question 4

Crosstalk types

Answer 4

Near end crosstalk (NEXT) Interference near transmitting end
Far end crosstalk (FEXT) Interference away from transmitting end
Alien crosstalk (AXT) Interference from other cables
Attenuation to Crosstalk Ratio (ACR) Difference between insertion loss and NEXT. Signal-to-noise ratio (SNR)

Question 5

Troubleshooting crosstalk

Answer 5

Mainly wiring, crimps could be bad. Maintain twist to minimize crosstalk. Test cable.

Question 6

Electromagnetic interference

Answer 6

Don’t twist cables, bend too much (bend radius), don’t use staples. Put cables away from poewr cords, flouresent lights, electrical systems, fire prevention components.

Question 7

Attenuation

Answer 7

Signal becomes weaker over distance.

Question 8

Termination troubleshooting

Answer 8

Use correct cable termination, test cable before use. Check if pairs are correct

Question 9

Interface monitoring

Answer 9

Use SNMP, check utilization, check errors and rate and use bandwidth test

Question 10

CRC error

Answer 10

Cyclic redundancy check. Checksum doesn’t match, possible corruption.

Question 11

Runts

Answer 11

Frame too small less than 64 bytes, sign of collision

Question 12

Giants

Answer 12

Frame larger than 1518 bytes or more than max frame size

Question 13

Drops

Answer 13

Frame not delivered due to contention

Question 14

Error disabled

Answer 14

Device disabled by interface due to error detected

Question 15

Administratively down

Answer 15

Device disabled by admin, usually due to error

Question 16

Suspended

Answer 16

Configuration not compatible, similar to error disabled

Question 17

Power budget exceeded

Answer 17

PoE switch may not have enough power

Question 18

Incorrect standard

Answer 18

PoE specification may require too much power (PoE can’t power PoE+)

Question 19

Fiber transceivers

Answer 19

Must be same wavelength, must be single or multimode

Question 20

Transceiver strength

Answer 20

Must have enough signal. Check power budget, distance, connectors, splices, check sensitivity level