Noise is unwanted electrical signals that find their way onto the wire. If the noise is low then it will not interfere with the communication. If the noise is too high then it will begin to interfere with the signal. Noise can come from other cables in the circuit or from external sources. To overcome problems with noise shielded cable can be used.
Many outside factors can contribute to interference on the networking media.
Some examples of sources that can produce outside signals that can impose themselves on wire pairs in UTP cable include:
- Fluorescent lights
- Air cleaners
- Motion sensors
- Electronic devices of all kinds
Fortunately, signals produced by these outside sources often occupy specific frequencies. This enables an electrical noise level test to not only detect such outside interferences, but to narrow the range of possible sources that produced them.
Skew is a problem related to timing in parallel cables. If data is carried over multiple lines (parallel) it is possible that the data may arrive at different times at the receiver
Note: Skew is not possible in serial communications.