Network Cabling - Study Notes

Chapter Summary

This chapter is about the physical cables that connect computers in a network. It describes coaxial cable, twisted pair cable (UTP and STP), fibre optic cable, USB cable, and serial and parallel cables. Wired connections are generally faster and more secure than wireless ones. The chapter then explains the parts of an Ethernet cable, the T568A and T568B wiring standards, the crimping tool and the different registered jacks.

Learning Objectives

• Explain why cabling matters in a computer network.
• Identify and compare the different types of network cable.
• Name the components used to make an Ethernet cable.
• Tell apart the registered jack types and what each is used for.
• Apply the standard wiring schemes and colour codes.

Key Concepts and Definitions

• Node: Any device connected to a network, identified by its IP address.
• Coaxial Cable: A cable with a central copper conductor surrounded by insulation, a metal shield and an outer cover. It is mainly used for cable television.
• Twisted Pair Cable: A cable in which insulated copper wires are twisted together in pairs. The twisting reduces interference from outside electrical noise.
• Fiber Optic Cable: A cable made of thin glass or plastic fibres that carries data as pulses of light. It suits fast connections over long distances.
• RJ45 Connector: The eight-pin plastic connector fitted at the ends of an Ethernet cable.
• Crimping: Pressing a connector onto the wires with a crimping tool so that the two are firmly joined.

Worked Methods

Ethernet Cable Fabrication (Crimping Process)

These are the steps to make an Ethernet cable with a crimping tool:

1. Cut the twisted pair cable to the length you need.
2. Strip about 1 inch of the outer jacket from both ends so the twisted pairs are visible.
3. Untwist the small wires and arrange them in the correct colour order. T568B is the order most commonly used.
4. Hold the wires flat together and trim them evenly to about half an inch.
5. Push all eight coloured wires into the eight slots of the RJ45 connector, so that the outer jacket also goes a little way inside the connector.
6. Squeeze the crimping tool firmly. The connector should stay fixed when you pull the cable by hand.
7. If needed, check the finished cable with a cable tester.

Wiring Standard Selection

The type of cable depends on which devices you are connecting:

• Straight-Through: Both ends use the same colour order. Use it to connect different kinds of devices, such as a computer to a hub or switch.
• Crossover: The transmit and receive pairs are swapped, so pin 1 at one end goes to pin 3 at the other and pin 2 goes to pin 6. Use it to connect two similar devices directly, such as one PC to another, without a hub.
• Rollover: The pin order at one end is the complete reverse of the other (pin 1 to pin 8, pin 2 to pin 7, and so on). It is used as a console cable to configure a router or switch.

Common Exam Traps

• RJ11 vs. RJ45: RJ11 is the smaller connector with six pins, used for telephone lines. RJ45 is wider, has eight pins and is used for Ethernet LAN cables.
• Wrong crossover mapping: A crossover cable does not reverse every wire. Only the transmit and receive pairs (the orange and green pairs) change places: pins 1 and 2 swap with pins 3 and 6.
• Ignoring shielding: In places with heavy electrical interference, such as factories, shielded twisted pair (STP) is needed. Unshielded twisted pair (UTP) picks up too much noise there.

Exam Tips

• In 10 and 100 Mbps Ethernet only the orange and green pairs carry data; the blue and brown pairs are unused. Gigabit Ethernet uses all four pairs.
• RJ21 is known as the champ connector and has 50 pins. It is used where many telephone lines are brought together.
• On a network port, a blinking light (orange on many cards) shows that data is being sent or received over the link.
• Make sure the outer jacket is gripped inside the connector when you crimp, so a pull on the cable does not strain the thin wires.