Endpoints and Media Types · Topic 1 of 5
Network Cables and Connectors
Identify copper, twisted pair, coaxial and fiber optic cables, the RJ-45, RJ-11, coax and fiber connectors, and which cable fits which job on a LAN.
- 4 min
- Twisted pair, coax and fiber are the three main cable types.
- UTP is unshielded. STP has a shield for noisy places.
- Ethernet over twisted pair reaches 100 metres in one run.
What it is
A network cable is the physical medium that carries data between devices, and a connector is the plug at its end.
Most cables are copper or fiber. Copper carries electrical signals and fiber carries pulses of light.
Choosing the right cable and connector depends on the speed you need, the distance, and the surroundings. This page lists the ones you are expected to recognise.
How it works
Each cable type has its own construction, its own connector and its own limits.
Twisted pair copper
Twisted pair cable holds four pairs of copper wires. The wires in each pair are twisted around each other, which cancels out much of the electrical noise.
There are two main kinds. UTP (unshielded twisted pair) is the common type in offices and homes. STP (shielded twisted pair) has a metal shield that gives extra protection in electrically noisy places.
Twisted pair is graded in categories.
| Category | Typical use |
|---|---|
| Cat 5e | Up to 1 Gbps |
| Cat 6 | 1 Gbps, and 10 Gbps over short runs |
| Cat 6a | 10 Gbps over the full distance |
For Ethernet over twisted pair, the maximum length of one cable run is 100 metres. A straight through cable connects unlike devices, such as a PC to a switch. A crossover cable connects like devices, such as switch to switch, though most modern ports sort this out automatically.
Coaxial cable
Coaxial cable, or coax, has a centre copper wire surrounded by insulation, a metal shield and an outer jacket. It is used for cable television and for broadband delivered by a cable operator.
Its usual connector is the screw on F connector. Older networks also used the BNC connector for coax, but it is rare today.
Fiber optic cable
Fiber cable carries light through a thin strand of glass. It is not affected by electrical interference, it reaches far, and it supports very high speeds.
There are two types.
| Type | Core | Light source | Distance |
|---|---|---|---|
| Single mode | Very thin | Laser | Long, many kilometres |
| Multimode | Thicker | LED or similar | Shorter, inside a building or campus |
Fiber is more costly to fit than copper, and the glass can be damaged if it is bent too sharply.
Connectors
| Connector | Used for | Notes |
|---|---|---|
| RJ-45 | Ethernet over twisted pair | Eight pins, wider than a phone plug |
| RJ-11 | Telephone lines and DSL | Smaller than RJ-45 |
| F connector | Coax | Screws on |
| LC | Fiber | Small and square, held by a clip |
| SC | Fiber | Square, push in and pull out |
| ST | Fiber | Round, twist on |
A fiber link needs two strands, one for each direction. A fiber patch cable therefore usually has two connectors at each end.
Most home and office LAN ports are RJ-45. If a device has a smaller socket for a phone line, it is RJ-11.
What to remember for the exam
Seven facts cover most questions on this topic.
- Twisted pair, coax and fiber are the three main cable types.
- UTP is unshielded. STP has a shield for noisy places.
- Ethernet over twisted pair reaches 100 metres in one run.
- RJ-45 is the Ethernet connector. RJ-11 is the telephone connector.
- Coax uses the F connector, and the cable is used for cable television and cable broadband.
- Single mode fiber uses a laser and reaches long distances. Multimode fiber is for shorter runs.
- LC, SC and ST are common fiber connectors.
Count the pins. A wide plug with eight contacts is RJ-45, and a narrow plug is RJ-11.
Common mistakes
These four errors appear again and again.
Mixing up RJ-45 and RJ-11. The RJ-45 is wider and is used for Ethernet. The RJ-11 is narrower and is used for telephones.
Running a copper cable too far. A twisted pair run beyond 100 metres may cause errors, so use fiber or add a device in between.
Using multimode fiber for a long link. Multimode is for shorter distances, and single mode is the choice for long ones.
Thinking fiber carries electricity. It carries light, which is why it is not affected by electrical noise.
Do not bend fiber into a tight loop. A sharp bend can damage the glass or weaken the signal.
Check yourself
Work through these three questions.
What is the maximum length of one Ethernet twisted pair cable run?
The maximum is 100 metres.
Which connector is used for Ethernet and which for a telephone line?
RJ-45 is used for Ethernet and RJ-11 is used for a telephone line.
Why would you choose fiber over copper in an electrically noisy factory?
Fiber carries light, so electrical interference does not affect it.
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