5.2 Given a scenario, troubleshoot common cabling and physical interface issues
Cable Issues
📘CompTIA Network+ (N10-009)
Signal degradation happens when the quality of the data signal traveling over a network cable decreases. This can cause slower speeds, errors, or complete network failures. In the Network+ exam, you need to understand the main causes of signal degradation, which are crosstalk, interference, and attenuation.
1. Crosstalk
Definition:
Crosstalk happens when signals from one cable or wire interfere with signals in another cable or wire. Think of it as “signal leakage” from one wire to another.
Why it matters:
- Crosstalk can corrupt data, leading to errors and retransmissions.
- It is most common in twisted pair cables like Cat5e, Cat6, and Cat6a.
Types of Crosstalk:
- Near-End Crosstalk (NEXT): Interference detected at the same end of the cable where the signal is sent.
- Far-End Crosstalk (FEXT): Interference detected at the opposite end of the cable.
IT Example:
- If you have multiple network cables running through the same patch panel or conduit, the data on one cable can interfere with another.
- High-speed networks like 10GBASE-T are more sensitive to crosstalk, so proper cable selection and installation matter.
How to reduce it:
- Use shielded twisted pair (STP) instead of unshielded (UTP) if interference is high.
- Ensure proper twisting of wires inside the cable.
- Avoid running network cables parallel to electrical cables.
2. Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI)
Definition:
Interference happens when external sources affect the signal on the cable.
- EMI: Comes from electrical devices (motors, fluorescent lights, microwaves).
- RFI: Comes from wireless signals or radio transmissions.
Why it matters:
- Interference causes data errors, packet loss, and network performance issues.
IT Example:
- Running Ethernet cables close to a large server power supply or near Wi-Fi antennas may cause interference.
- A network switch might see errors on ports because the signal is being disturbed by nearby devices.
How to reduce it:
- Use STP or fiber optic cables (fiber is immune to EMI/RFI).
- Keep network cables away from high-power devices.
- Properly ground cables in STP installations.
3. Attenuation
Definition:
Attenuation is the weakening of a signal as it travels along a cable. The longer the cable, the more the signal weakens.
Why it matters:
- When the signal is too weak, devices cannot communicate correctly.
- Attenuation depends on cable type, length, and quality.
IT Example:
- A Cat5e cable has a maximum length of 100 meters. If you exceed this, the network signal may degrade, causing slow speeds or disconnections.
- Fiber optic cables can travel much farther, but even they experience some attenuation over very long distances.
How to reduce it:
- Keep cable lengths within the standard limits (e.g., 100m for Cat5e/Cat6, depends on fiber type).
- Use repeaters, switches, or signal boosters if longer distances are needed.
- Choose higher-quality cables with lower attenuation ratings for critical connections.
Quick Summary Table for Exam
| Term | Definition | Cause / Example in IT | How to Fix / Prevent |
|---|---|---|---|
| Crosstalk | Signal interference between wires | Multiple cables close together | STP cables, proper twisting, avoid parallel runs |
| Interference | External signals affecting network signals | Electrical motors, fluorescent lights | Use STP or fiber, proper grounding, cable routing |
| Attenuation | Weakening of the signal over distance | Cable longer than max spec | Keep cables within limits, use repeaters, higher-quality cables |
Key Exam Tips:
- Know the difference between crosstalk, interference, and attenuation.
- Remember STP vs UTP and fiber advantages in reducing degradation.
- Be able to identify the cause based on the scenario: e.g., EMI near fluorescent lights → interference; very long cable → attenuation; multiple close cables → crosstalk.
