Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define and differentiate between various network topologies.
• Describe different communication media like cables and wireless.
• Select appropriate technologies for a given scenario.
• Explain factors that affect network performance.
• Troubleshoot basic network connectivity issues.

Lesson summary

In today's interconnected world, understanding computer networks is no longer a luxury, but a necessity. From accessing educational resources online to connecting with family and friends across South Africa (and the globe), networks play a crucial role in our daily lives. Whether it's using Wi-Fi in a local internet cafe in Soweto, accessing online banking from your phone in Durban, or participating in online learning from a rural school in Limpopo, networks are the unseen infrastructure that makes it all possible.

Lesson notes

Network Topologies A network topology defines the physical or logical arrangement of devices in a network. Different topologies offer different advantages and disadvantages in terms of cost, reliability, scalability, and performance.

Bus Topology: In a bus topology, all devices are connected to a single cable, called the backbone or bus.

Advantages: Simple and inexpensive to implement for small networks.

Disadvantages: If the backbone cable fails, the entire network goes down. Performance degrades as more devices are added due to collisions (multiple devices trying to transmit data simultaneously). Difficult to troubleshoot.

Example: Imagine a single electrical cable running through a small office, with each computer plugged into it. While cheap to set up initially, if someone accidentally cuts the cable, everyone loses their connection.

Star Topology: In a star topology, all devices are connected to a central hub or switch.

Advantages: Relatively easy to install and troubleshoot. If one device fails, it doesn't affect the rest of the network. Easy to add or remove devices.

Disadvantages: If the central hub or switch fails, the entire network goes down. Requires more cable than a bus topology.

Example: Think of a school computer lab where all the computers are connected to a central switch. If one student's computer malfunctions, it won't affect the other students' ability to work.

Ring Topology: In a ring topology, each device is connected to two other devices, forming a closed loop. Data travels in one direction around the ring.

Advantages: Relatively simple to implement. Data can be transmitted efficiently if well-managed.

Disadvantages: If one device or cable fails, the entire network can go down. Difficult to troubleshoot. Adding or removing devices can disrupt the network.

Example: Picture a small security system where each sensor is connected to the next in a circular fashion. If one sensor fails, the whole system might be compromised.

Mesh Topology: In a mesh topology, each device is connected to many or all other devices.

Advantages: Highly reliable. If one connection fails, data can be rerouted through other connections.

Disadvantages: Very expensive and complex to implement, especially for large networks. Requires a lot of cabling.

Example: Consider a network of radio towers in a remote area. Each tower is connected to multiple other towers, ensuring that communication can continue even if one tower fails. This provides redundancy, crucial for emergency services.

Tree Topology: A tree topology combines features of bus and star topologies. Multiple star networks are connected to a bus backbone.

Advantages: Scalable and flexible. Easier to manage than a large bus network.

Disadvantages: If the backbone cable fails, entire segments of the network are affected. More complex to configure and troubleshoot than star or bus topologies.

Example: Imagine a university campus where each department has its own star network, and all the department networks are connected to a central backbone network. This allows for decentralized management while still providing overall connectivity. Communication Media Communication media are the physical channels through which data is transmitted in a network. The choice of medium depends on factors such as distance, bandwidth requirements, cost, and security.

Twisted-Pair Cable: Consists of pairs of wires twisted together to reduce interference.

UTP (Unshielded Twisted Pair): Commonly used for Ethernet networks. Relatively inexpensive and easy to install. Susceptible to interference.

Example: The standard network cable you use to connect your computer to the school network or your home router.

STP (Shielded Twisted Pair): Contains a foil or braid shield to further reduce interference. More expensive than UT

P. Example: Used in environments with high levels of electromagnetic interference, such as factories or near power lines.

Coaxial Cable: Consists of a central conductor surrounded by insulation and a metallic shield. Offers better resistance to interference than UT

P. Example: Traditionally used for cable TV connections. Still used in some older network installations.

Fiber Optic Cable: Transmits data as pulses of light through glass or plastic fibers. Offers very high bandwidth and is immune to electromagnetic interference. More expensive than copper cables.

Example: Used for long-distance communication, such as connecting different cities or continents. Also used in data centers where high bandwidth is critical. Imagine the undersea cables connecting South Africa to Europe, transmitting vast amounts of data every second.

Wireless Technologies: Transmit data through the air using radio waves.

Wi-Fi (Wireless Fidelity): Most common wireless technology used in homes, offices, and public hotspots. Provides relatively high bandwidth over short distances.

Example: Connecting your smartphone or laptop to the internet at a coffee shop in Cape Town.