CompTIA Network+ Preparation · lesson 28 of 30 · 25 min
Copper Cabling
Copper cabling transmits data as electrical signals. The most common type in LANs is twisted-pair Ethernet cable.
UTP (Unshielded Twisted Pair) — most common LAN cable. Pairs of wires twisted together to reduce crosstalk and EMI. No shielding.
STP (Shielded Twisted Pair) — has metallic shielding around pairs or the entire cable. Better EMI protection. Used in industrial environments.
Coaxial cable — central conductor surrounded by insulation, shielding, and outer jacket. Used for cable TV, older Ethernet (10BASE2, 10BASE5), and cable broadband.
Fiber Optic Cabling
Fiber optic cables transmit data as light pulses. Immune to EMI, supports much longer distances and higher speeds than copper.
SMF (Single-Mode Fiber) — small core (8–10 µm). Single light path. Long distances (up to 100 km). Used for WAN and campus backbones. Requires laser light source. More expensive.
MMF (Multi-Mode Fiber) — larger core (50–62.5 µm). Multiple light paths. Shorter distances (up to 2 km). Used for building/campus LANs. Uses LED or VCSEL light source. Less expensive.
Fiber connectors: LC (small form factor, most common in data centers), SC (square connector, push-pull), ST (bayonet twist-lock, older), MPO/MTP (multi-fiber, high-density).
Transceivers: SFP (1 Gbps), SFP+ (10 Gbps), QSFP (40 Gbps), QSFP28 (100 Gbps). Hot-swappable modules that convert between electrical and optical signals.
Exam Tip
SMF = single-mode = long distance (yellow jacket). MMF = multi-mode = shorter distance (orange or aqua jacket). Cat 6a supports 10 Gbps at full 100m. LC connectors are most common in modern data centers.
Cable Issues and Tools
Crosstalk — interference between adjacent wire pairs. NEXT (Near-End Crosstalk), FEXT (Far-End). Twisting reduces crosstalk.
Attenuation — signal loss over distance. All cables have a maximum distance specification.
Cable tester — verifies continuity and correct wiring. Identifies opens, shorts, and miswires.
TDR (Time Domain Reflectometer) — sends a pulse and measures reflections to locate cable faults (breaks, shorts) and measure cable length.
OTDR (Optical TDR) — same concept for fiber optic cables.
Straight-through cable — same pinout on both ends (T568A-T568A or T568B-T568B). Used to connect different device types (PC to switch).
Crossover cable — T568A on one end, T568B on the other. Used to connect same device types (switch to switch, PC to PC). Modern switches use Auto-MDIX to detect and adjust automatically.
Key Terms
Key Terms
Knowledge Check — 10 Questions
Network+ — Cabling and Physical Layer
Which cable category supports 10 Gbps at the full 100m distance?
- Cat 5e
- Cat 6
- Cat 6a
- Cat 7
Answer: Cat 6a
Cat 6a (Augmented) supports 10 Gbps at 100m. Cat 6 supports 10G only up to 55m. Cat 5e supports 1 Gbps.
Single-Mode Fiber (SMF) is used for:
- Short building runs
- Long-distance WAN and campus backbones
- Wireless connections
- Copper replacement in desktops
- Answer: Long-distance WAN and campus backbones
SMF has a small core and uses laser light — supports distances up to 100 km. Used for WAN links and long campus runs. A TDR is used to:
- Test wireless signal strength
- Locate cable faults and measure cable length
- Verify IP connectivity
- Measure fiber light levels
- Answer: Locate cable faults and measure cable length
TDR sends a pulse and measures reflections — can pinpoint breaks, shorts, and impedance mismatches, and measure cable length.
Multi-Mode Fiber (MMF) uses which light source?
- Laser only
- LED or VCSEL
- Infrared only
- Visible light only
Answer: LED or VCSEL
MMF uses LED or VCSEL (Vertical-Cavity Surface-Emitting Laser) light sources. SMF uses laser. MMF is less expensive.
Crosstalk in copper cabling is reduced by:
- Adding shielding only
- Twisting the wire pairs
- Using larger conductors
- Reducing cable length
- Answer: Twisting the wire pairs
Twisting pairs causes interference from adjacent pairs to cancel out — the fundamental principle of twisted-pair cabling. Auto-MDIX eliminates the need for:
- Cable testers
- Crossover cables between same-type devices
- Fiber transceivers
- VLAN configuration
- Answer: Crossover cables between same-type devices
Auto-MDIX automatically detects the cable type and adjusts — you can use a straight-through cable between two switches. LC connectors are most commonly used in:
- Legacy coaxial networks
- Modern data center fiber connections
- Cat 5e patch panels
- Telephone wiring
- Answer: Modern data center fiber connections
LC (Lucent Connector) is small form factor — the dominant fiber connector in modern data centers and SFP transceivers. SFP+ transceivers support:
- 1 Gbps
- 10 Gbps
- 40 Gbps
- 100 Gbps
- Answer: 10 Gbps
SFP = 1 Gbps. SFP+ = 10 Gbps. QSFP = 40 Gbps. QSFP28 = 100 Gbps. These are hot-swappable fiber/copper modules. A straight-through cable connects:
- Switch to switch
- PC to PC
- PC to switch (different device types)
- Router to router
- Answer: PC to switch (different device types)
Straight-through cables connect different device types (PC to switch, switch to router). Crossover connects same types (switch to switch).
SMF fiber typically has a yellow jacket; MMF typically has an _____ or aqua jacket.
Answer: orange
Color convention: SMF = yellow jacket. MMF = orange (OM1/OM2) or aqua (OM3/OM4). Helps identify fiber type in the field.
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