Copper cables

What does NEXT stand for in network cables?

• Near End CrossTalk

• Refers to interference between wire pairs in cable

  • measured at the TX end

What does PSNEXT stand for in network cables?

• Power Sum Near End Crosstalk

• Cumulative interference effect from multiple wire pairs in twisted pair Ethernet cable

• Combines NEXT values from all pairs to evaluate overall crosstalk

How can the next value of a pair in a network cable be calculated?

-20 \cdot \text{log}_{10} \frac{V_{next}}{V_{in}}

How can the PSNEXT value of a network cable be calculated?

• Convert NEXT values of individual pairs to absolute values (10^)

• Sum individual NEXT values up

-10 * \text{log}_{10} (10^{-\frac{NEXT_{n}}{10}} + ...)

What is the attenuation crosstalk ratio?

• Tells you how much data you can actually send

• ACR = NEXT - Attenuation

• PSACR = PSNEXT - Attenuation

Example:

we send 1 V, due to attenuation, 0,1 V arrive. If there's another wire where the recipient sends 1 V, this 1 V might change the received 0,1 V to e.g. 0V -> crosstalk so high, we can't read the sent signal anymore.

What is the signal to noise ratio in the context of copper cables in networking?

• "Distance" between signal level and noise level

• Important information for transmission quality (dB)

• Similar to ACR

SNR = 20 \cdot \text{log}_{10} \frac{V_{Signal}}{V_{Noise}}

What is referred to by the term "Alien Crosstalk"?

• Crosstalk between adjacent cables

• Additionally takes into account other influences like EMI and Radio Frequency Interference

• Becomes especially important at 10 gigabits

What are the different shielding types for copper cables in networking?

• UTP or U/UTP: Unshielded Twisted Pair -> no shielding

• STP or S/UTP: Screened Unshielded Twisted Pair

  • Also called "fully shielded twisted pair" or "foiled twisted pair"

  • Common braiding sheathing of all wire pairs together

• STP or U/FTP: Shielded Twisted Pair

  • Foil sheathing for each individual wire pair; no outher shielding

• STP or F/FTP: Screened (fully) Shielded Twisted Pair

  • Shielding like U/FTP and S/UTP together

What does Unshielded TP shield against in the context of copper cables in networking?

• Nothing, insulation only

What does Shielded TP shield against in the context of copper cables in networking?

• PS-Crosstalk

• Alien-Crosstalk

What does Screened Unshielded TP shield against in the context of copper cables in networking?

• Alien Crosstalk

What does Fully Shielded TP shield against in the context of copper cables in networking?

• PS-Crosstalk

• Alien-Crosstalk

How can the shielding of a copper cable be abbreviated?

• In the form of xx/xxx

• First part -> overall screen

  • F = foil screened

  • S = braid screened

  • SF = braid and foil screened

• Second part -> element screen

  • U = unscreened

  • F = foil screened