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Flashcards in Copper Wiring Troubleshooting Facts Deck (23):
1

Electromagnetic interference (EMI) & Radio Frequency Interference (FRI)

* External signals that interfere with normal network communications

2

Common sources of EMI/RFI

* Nearby generators
* motors ( such as elevator motors)
* radio transmitters
* welders
* transformers
* fluorescent lighting

3

How to protect against EMI/FRI

* Use fiber instead of copper (fiber immune to EMI/RFI)
* Use shielded twisted pair cables (they have a metal foil that encloses all of the wires. some might include a drain wire (a bare wire in the cable that absorbs EMI/RFI)
* Avoid installing cables near EMI/RFI sources

4

Crosstalk

* interference that is caused by signals within the twisted pairs of wires.
* Ex. current flow on one wire causing a current flow on an adjacent wire

5

Crosstalk Facts

* Twisting of wires into pairs helps reduce crosstalk between wires
* Each pair of wires is twisted at a different rate to reduce crosstalk between pairs
* Crosstalk is often introduced within connectors, where the twists are removed to add the connector. Crosstalk can also occur where wires are crushed or where the plastic coating is worn

6

Name three forms of crosstalk

* Near end crosstalk (NEXT)
* Far end crosstalk (FEXT)
* Alien crosstalk

7

Near end crosstalk (NEXT)

* Is measured on the same end as the transmitter
* Ex. when a signal is sent on one wire, near end crosstalk measures the interference on an adjacent wire at the same connector end

8

Far end crosstalk (FEXT)

* Measured on the opposite end from the transmitter
* Ex. when a signal is sent on one wire, far end crosstalk measures the interference on the adjacent wire at the opposite connector end

9

Alien crosstalk

* Is introduced from adjacent, parallel cables
* Ex. a signal sent on wire causes interference on a wire that is within a separate twisted pair cable bundle

10

Attenuation

* the loss of signal strength from one end of a cable to the other. This is also know a dB loss

11

Attenuation Facts

* The longer the cable, the more attenuation. For this reason it I important never to exceed the maximum cable length defined by the networking architecture
* Cables at higher temperature experience more attenuation than cables at a lower temperature
* A repeater regenerates the signal and removes the effects of attenuation

12

Open impedance mismatch (echo)

* the measure of resistance within the transmission medium

13

Open impedance mismatch Facts

* Impedance is measured in ohms
* All cables must have the same impedance rating. The impedance rating for the cable must match the impedance of the transmitting device
* Impedance is mostly a factor in coaxial cables used for networking

14

Open impedance mismatch Facts 2

* When signals move from a cable wit one impedance rating to a cable with another rating, some of the signal is reflected back t the transmitter, distorting the signal. With video (cable TV) impedance mismatch is manifested as ghosting of the image
* Cable distance does not affect the impedance of the cable

15

Shorts

* Occurs when electrical signals take a path other than the intended path.
* In twisted pair wiring a short means that a signal sent on one wire arrives on a different wire.
* Shorts occur wen tow wires touch this can be caused by worn wire jackets, crushed wires, or a metal objects piercing two or more wires

16

Open Circuit

* When a cut in the wire prevents the original signal from reaching the end of the wire
* Open circuit different from a short in that the signal stops ( electricity cannot flow because the path is disconnected)

17

Miswired

* Caused by incorrect wire positons on both connectors

18

Wiring Problems (Miswired)

* Reverse connection
* Wiremapping
* split pair

19

Reverse connection

* when a cable is wired using on standard on one end and another standard on the other end, creating a crossover cable
* While this might be intentional, it can cause problems when a crossover cable is used instead of a straight through cable

20

Wiremapping

* Refers to the matching of a wire with a pin in one end with the same pin on the other end
* Ex and error in the wiremapping results when the wire a pin 1 connects to pin 4

21

Split pair

* condition is when a single wire in two different pairs is reversed a both ends
* Ex. if instead of he solid green wire, the solid brown wire is matched with the green/white wire in pins 1 and 2. with a split pair configuration, the cable might still work especially if it is short but it could introduce crosstalk

22

Incorrect termination

* Occurs when an incompatible or incorrect connector is used. This can result in reduced performance or complete connection lost

23

Bad connector

* is a damaged connector that is casing connectivity issues.
* Ex a broken locking ab on a RJ45 connector can cause intermittent connection problems