5.2 Given a scenario, troubleshoot common cabling and physical interface issues
Cable Issues
📘CompTIA Network+ (N10-009)
Cabling is the foundation of any network. Using the wrong cable can cause network problems like slow connections, no connection, or frequent disconnections. In troubleshooting, understanding cable types is key.
We can divide cable issues into types of fiber and types of copper cabling.
1. Fiber Optic Cables: Single-mode vs Multimode
Fiber cables use light to transmit data instead of electricity. They are commonly used in data centers, enterprise networks, and connections between buildings.
Single-mode fiber (SMF)
- Core size: Very small (about 9 microns in diameter)
- Distance: Can transmit data over long distances (up to 40 km or more)
- Light source: Uses a laser
- Use case: Connecting two buildings in a campus network or long-haul internet connections
- Problem if used incorrectly:
- If you use single-mode fiber where multimode is required, the laser may not work properly, leading to signal loss or no connection.
Multimode fiber (MMF)
- Core size: Larger (about 50–62.5 microns)
- Distance: Shorter distances (up to 550 meters)
- Light source: Uses LED light
- Use case: Internal building networks, data center connections between switches and servers
- Problem if used incorrectly:
- Using multimode fiber for long-distance single-mode applications will cause high attenuation (signal loss) and connection failure.
Key point for the exam: Don’t mix single-mode and multimode fibers. Always check the type before connecting devices.
2. Copper Cables: Cat5, Cat5e, Cat6, Cat6a, Cat7, Cat8
Copper cables transmit data using electricity. These are commonly used for LANs, desktop connections, and switches.
| Cable Type | Max Speed | Max Distance | Shielding | Common Use |
|---|---|---|---|---|
| Cat5 | 100 Mbps | 100 m | UTP | Older networks, low-speed |
| Cat5e | 1 Gbps | 100 m | UTP | Standard for modern networks |
| Cat6 | 1 Gbps / 10 Gbps* | 100 m / 55 m for 10G | UTP/STP | Faster networks, small office |
| Cat6a | 10 Gbps | 100 m | STP | High-speed LANs |
| Cat7 | 10 Gbps | 100 m | Shielded (S/FTP) | Data centers, high interference areas |
| Cat8 | 25–40 Gbps | 30 m | Shielded | Server racks, high-speed short links |
Key troubleshooting points:
- Using Cat5 in a network that needs 10 Gbps won’t work. Devices may auto-negotiate to a slower speed or fail to connect.
- Using unshielded cables (UTP) in an area with high electromagnetic interference (near motors, fluorescent lights, or servers) can cause errors. Shielded cables (STP) may be required.
- Always check the cable type before troubleshooting speed or connectivity issues.
3. Shielded vs Unshielded (STP vs UTP)
UTP (Unshielded Twisted Pair)
- Common in offices and homes
- Less expensive, easier to install
- Susceptible to electromagnetic interference (EMI)
STP (Shielded Twisted Pair)
- Has extra shielding around the wires
- Reduces EMI, ideal for industrial environments or data centers
- Must be grounded properly; otherwise, it can cause more problems
Problem if used incorrectly:
- Using UTP in an area with lots of EMI → network errors, dropped packets
- Using STP but not grounding it → can create short circuits or interference
4. Exam Tips and Key Points
When troubleshooting cable issues:
- Check the cable type:
- Fiber: single-mode vs multimode
- Copper: Cat5e, Cat6, Cat6a, etc.
- Check the cable use case:
- High-speed network? Need Cat6a+
- Long-distance fiber? Use single-mode
- Check shielding:
- High interference? Use STP
- Look for physical issues:
- Wrong connectors (RJ45 vs LC/SC for fiber)
- Crimped incorrectly
- Check device compatibility:
- Devices may not support the cable speed/type
✅ Summary for the exam
- Using the wrong type of cable can cause network failures, slow speeds, or no connection.
- Always know fiber vs copper, single-mode vs multimode, cable categories, and shielding types.
- Proper selection and verification of cables is a core troubleshooting step
