Network Cabling and Signal Integrity

Signal Degradation

• Signal degrades over longer distances, known as attenuation.
• Attenuation affects both electrical signals over copper and light over fiber.
• Excessive attenuation results in signal loss that the receiver cannot interpret.

Measuring Signal Strength

• Signal strength is measured in Decibels (dB), 1/10 of a Bell, named after Alexander Graham Bell.
• Logarithmic scale:
  • 3 dB = 2x signal
  • 10 dB = 10x signal
  • 20 dB = 100x signal
  • 30 dB = 1,000x signal.
• Signal loss: losing half the signal equates to a 3 dB loss.

Troubleshooting Signal Issues

• Complete signal loss results in 0 dB signal.
• Intermittent signal can be observed through link lights but poor data transfer.
• CRC (Cyclic Redundancy Check) errors indicate data corruption.
• Use measurement tools for precise signal loss determination.

Electromagnetic Interference (EMI)

• EMI can affect signal integrity, caused by power cords, fluorescent lights, etc.

Cable Installation Best Practices

• Ensure cables are not damaged, twisted, pulled, or stretched.
• Follow manufacturer’s bend radius specifications.
• Use cable ties or Velcro instead of staples.

Connectors and Pin-Outs

• Correct pin-outs are crucial; use testing devices to verify.
• Straight-through cables connect pin 1 to pin 1, pin 2 to pin 2, etc.
• Incorrect pin-outs cause performance or connectivity issues.
• Specialists are recommended for accurate cabling.

Interface and Configuration Errors

• Hardware failure can cause interface errors.
• Verify speed, duplex, and VLAN configurations on switches and workstations.
• Auto vs manual configuration preferences.

Common Cable Issues

• Short Circuit: Internal insulators wear away, causing wires to touch.
• Open Circuit: Complete disconnection of the wire, requiring repair.
• Use TDR to diagnose issues within walls or ceilings.
• Replace damaged patch cables quickly.

Fiber-Optic Considerations

• Transceivers must match the type of fiber and wavelength (e.g., single mode, 850 nm).
• Mismatched transceivers lead to dropped frames and signal loss.
• Clean fiber connectors before use to prevent attenuation.

Auto-MDIX and Crossed Pairs

• Some ethernet devices can auto-correct crossed pairs using Auto-MDIX.
• Ensure end-to-end pin connections are accurate to avoid signal issues.