Network Topologies

This lesson covers network topologies — the arrangement of devices and connections in a network. You need to understand star, bus, mesh, and ring topologies, as well as the distinction between physical and logical topologies for the OCR H446 specification.

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What is a Network Topology?

A topology describes how devices (nodes) in a network are arranged and connected. Topology affects the network's performance, reliability, cost, and scalability.

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Physical vs Logical Topology

Type	Description
Physical topology	The actual physical layout of cables, devices, and connections
Logical topology	The way data flows through the network, regardless of physical layout

Example: A network may be physically wired as a star (all cables go to a central switch) but logically behave as a bus (data is broadcast to all devices).

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Star Topology

In a star topology, all devices are connected to a central device (typically a switch or hub). Devices communicate by sending data through the central device.

        [A]
         |
   [B]--[Switch]--[C]
         |
        [D]

Advantages

Advantage	Explanation
Fault isolation	If one cable or device fails, only that device is affected — the rest of the network continues
Easy to add devices	New devices connect directly to the central switch
Good performance	Dedicated connection between each device and the switch reduces collisions
Easy to troubleshoot	Faults can be identified quickly by checking individual cables

Disadvantages

Disadvantage	Explanation
Central point of failure	If the central switch/hub fails, the entire network goes down
More cabling	Each device needs its own cable to the central device
Higher cost	More cables and a central device increase costs

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Bus Topology

In a bus topology, all devices are connected to a single shared cable (the backbone or bus). Terminators are placed at each end of the bus to prevent signal reflection.

  [T]---[A]---[B]---[C]---[D]---[T]
  (T = terminator)

Advantages

Advantage	Explanation
Low cost	Uses less cabling than star topology
Simple to set up	Easy to install for small networks
No central device	No switch or hub required

Disadvantages

Disadvantage	Explanation
Single point of failure	If the backbone cable fails, the entire network goes down
Collisions	Multiple devices sharing one cable leads to data collisions
Poor performance under load	Performance degrades as more devices are added
Difficult to troubleshoot	Hard to locate where a fault has occurred on the bus
Security	All data is broadcast to all devices on the bus
Limited scalability	Adding more devices reduces performance

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Mesh Topology

In a mesh topology, devices are connected to multiple other devices, providing redundant paths for data.

Full Mesh

Every device is connected directly to every other device.

  [A]---[B]
  |\   /|
  | \ / |
  | / \ |
  |/   \|
  [C]---[D]

Partial Mesh

Some devices are connected to several others, but not all devices are interconnected.

Number of Connections in Full Mesh