Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define and describe common network topologies.
• Explain different types of communication media.
• Compare communication media based on bandwidth, cost, and security.
• Identify factors for selecting appropriate technologies.
• Create simple network diagrams.

Lesson summary

This week, we delve into the fascinating world of network topologies and communication media. Understanding how networks are structured and the technologies used to transmit data is crucial in our increasingly connected society. From accessing online learning resources to conducting business or simply staying in touch with family and friends, networks are fundamental to our modern lives, especially in South Africa where reliable connectivity is essential for bridging the digital divide and promoting economic growth. Imagine the impact of fast and reliable internet access in rural Limpopo, enabling students to access online learning platforms or small businesses to reach customers nationwide.

Lesson notes

2.1 Network Topologies A network topology refers to the physical or logical arrangement of devices (nodes) and connections (links) in a network. It essentially describes how different devices are interconnected.

Bus Topology: In a bus topology, all devices are connected to a single cable called the "backbone" or "bus." Advantages: Simple to implement and relatively inexpensive, requiring less cabling compared to other topologies.

Disadvantages: A break in the bus cable disrupts the entire network. Difficult to troubleshoot. Low security due to all data traversing the same cable. Not scalable. Performance degrades as more devices are added.

Example: Older Ethernet networks sometimes used bus topologies. Imagine a small spaza shop setting up a basic network for its point-of-sale system – a bus topology could be used if only a few devices were involved but it's not recommended for reliability.

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

Advantages: Easy to troubleshoot. A failure in one device or cable does not affect the entire network. Relatively easy to add or remove devices. High scalability.

Disadvantages: Requires more cabling than a bus topology. The central hub or switch is a single point of failure. Dependent on the central hub to function, if it fails, the whole network fails.

Example: This is the most common topology used in homes and small businesses today. Consider a cyber cafe in Johannesburg with multiple computers connected to a central switch – this is a star topology.

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

Advantages: Relatively simple to implement. Can be highly efficient if properly managed.

Disadvantages: A break in the ring cable disrupts the entire network. Difficult to troubleshoot. Adding or removing devices can disrupt the network. Relies on each node to pass the data further around the ring.

Example: Older token ring networks used this topology. While less common now, it provides a useful example of how networks used to function.

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

Advantages: Highly resilient. Redundancy ensures that data can still be transmitted even if some connections fail. Excellent fault tolerance.

Disadvantages: Very expensive to implement due to the high amount of cabling required. Difficult to manage.

Example: Used in critical infrastructure where reliability is paramount, such as connecting core routers in the Internet backbone or in military communications networks. Imagine the communications network used by Eskom to monitor and control the national power grid - a mesh topology could ensure resilience.

Tree Topology: A tree topology combines characteristics of the bus and star topologies. It has a hierarchical structure with a root node and branches.

Advantages: Scalable. Easy to manage. A failure in one branch does not affect the entire network.

Disadvantages: A failure in the root node disrupts the entire network. More complex to configure than a star or bus topology.

Example: Often used in larger organizations with multiple departments, where each department has its own star network, and these networks are connected to a central "backbone" network. Consider a University with different departments connected using separate star topologies, which are then connected to a central server using a tree topology.

Hybrid Topology: A hybrid topology combines two or more different topologies.

Advantages: Flexible and adaptable to different network requirements. Can be optimized for specific needs.

Disadvantages: Can be complex to manage and troubleshoot.

Example: A large company might use a combination of star and mesh topologies to connect different departments and ensure high availability. For example, a bank with its headquarters (using a star topology) connected to regional branches (also using star topologies) via a mesh network to ensure continuous communication even if some links fail. 2.2 Communication Media Communication media are the physical pathways through which data is transmitted in a network.

Twisted-Pair Cable: Consists of two insulated wires twisted together to reduce electromagnetic interference.

Types: Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP).

Advantages: Relatively inexpensive and easy to install.

Disadvantages: Limited distance (typically up to 100 meters). Susceptible to interference. Lower bandwidth compared to other media.

Example: Commonly used for connecting computers to a local area network (LAN) in offices and homes. Think of the Ethernet cable connecting your computer to your home router.

Coaxial Cable: Consists of a central copper conductor surrounded by insulation, a braided metal shield, and an outer jacket.

Advantages: Higher bandwidth than twisted-pair cable. Less susceptible to interference.