Network Cabling and Connectors Explained (Network+)
What you’ll know
Which copper category carries which speed and how far, when fiber is the answer, how to tell connectors apart, how much power PoE delivers, and which tool finds which cable fault. Then read your own link speed.
Why it matters. Layer 1 is the first place the troubleshooting method looks, and “the network is slow on one desk” is often a cable that negotiated 100 Mbps instead of 1 Gbps. The exam expects you to match cables, speeds and connectors from memory.
Copper: twisted pair
| Category | Speed | Max distance |
|---|---|---|
| Cat5e | 1 Gbps | 100 m |
| Cat6 | 1 Gbps (10 Gbps up to about 55 m) | 100 m |
| Cat6a | 10 Gbps | 100 m |
| Cat8 | 25–40 Gbps | 30 m (data centers) |
- UTP vs STP: unshielded is normal; shielded resists electrical noise (EMI) near motors and power lines.
- Plenum vs PVC jacket: plenum-rated cable gives off less toxic smoke and is required in air-handling spaces such as drop ceilings.
- T568A and T568B are the two wiring orders. Same standard on both ends = straight-through (normal). A on one end and B on the other = crossover, which modern ports rarely need because auto-MDIX sorts it out.
- Coax (RG-6, RG-59) carries cable TV and cable internet; twinax is the short copper “direct attach” cable between data-center switches.
Fiber
| Type | Distance | Light source | Typical jacket |
|---|---|---|---|
| Single-mode (SMF) | Kilometres | Laser | Yellow |
| Multimode (MMF) | Hundreds of metres | LED or VCSEL | Aqua or orange |
Fiber ignores electrical noise and can’t be tapped by induction. Ethernet names tell you the medium: 1000BASE-T and 10GBASE-T are copper; SR (short reach) runs on multimode; LR (long reach) on single-mode.
Connectors and modules
| Connector | Used for | How to spot it |
|---|---|---|
| RJ45 | Copper Ethernet | The familiar 8-pin plug |
| RJ11 | Phone lines | Smaller, 4–6 positions |
| LC | Fiber (most common today) | Small, push-pull latch, usually in pairs |
| SC | Fiber | Square, push-pull |
| ST | Fiber (older) | Round bayonet, twist to lock |
| MPO | Many fibers at once | Wide, rectangular, for 40/100 Gbps |
| SFP / SFP+ / QSFP | Plug-in transceivers in switch ports | Slot modules that take fiber or copper |
UPC vs APC fiber ends: APC is polished at an angle and usually green. Never mate APC with UPC; the angled face won’t meet the flat one and the link suffers.
Power over Ethernet
| Standard | Name | Power at the switch port |
|---|---|---|
| 802.3af | PoE | 15.4 W |
| 802.3at | PoE+ | 30 W |
| 802.3bt | PoE++ | 60 W (Type 3) or 90 W (Type 4) |
PoE powers phones, cameras and access points through the data cable. If a camera reboots at night when its infrared lights switch on, check whether the port’s power budget is enough.
Finding cable faults
| Symptom | Likely cause | Tool |
|---|---|---|
| No link light | Broken or unplugged cable, wrong pinout | Cable tester |
| Which cable in the bundle? | Unlabelled run | Toner and probe |
| Errors, slow, drops | Crosstalk, damage, EMI, too long | Certifier, TDR (copper), OTDR (fiber) |
| Fiber link dark or weak | Dirty connector, sharp bend | Light meter, fiber inspection scope |
| Port or NIC suspect | Hardware fault | Loopback plug |
A cable that’s 105 metres long works fine. Mostly. On Tuesdays. Then it doesn’t. Stick to 100. — Nyx
Read your own link
$ ethtool eth0 | grep -E "Speed|Duplex|Link detected" PS> Get-NetAdapter | Select-Object Name, LinkSpeed, MediaConnectionState
Replace eth0 with your interface name (ip -br link lists them). A wired link showing 100 Mbps or Half duplex on gigabit gear points at the cable or a damaged pair. In a VM, these show the virtual adapter, not your real cable.
Practise it
These topics are in the Network+ practice test, scored by exam domain.
NextCloud networking and SDN explained→
Go deeper
- Troubleshooting capstone — Ticket 1 is a dead link
- Your first Wireshark capture — see what actually crosses the wire
Explainer, written by StashGrid with AI help and checked against the CompTIA Network+ N10-009 objectives and the published standards (IEEE 802.11 and 802.3, TIA-568) before publishing. Speeds and distances are the standard ratings; real-world results are lower. StashGrid isn’t affiliated with CompTIA. Spotted an error? Tell us.