1.5 Network Topology

Network topology refers to the physical or logical arrangement of nodes (computers, devices) and the connections (links) between them in a network. The choice of topology directly affects a network's scalability (ability to grow) and reliability (ability to continue functioning when components fail).

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Types of Network Topology

1. Bus Topology

In a Bus topology, all nodes are connected to a single central cable called the backbone.

• Data travels along the backbone in both directions.
• Terminators are placed at both ends of the cable to absorb signals and prevent signal reflection (bounce).
• If the backbone cable fails, the entire network goes down.

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2. Star Topology

In a Star topology, all nodes are connected to a central device (Hub or Switch).

• All data passes through the central device.
• If the central device fails, the entire network goes down.
• If a single node fails, the rest of the network is unaffected.
• New nodes can be added easily without disrupting the network.

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3. Ring Topology

In a Ring topology, each node is connected to exactly two other nodes, forming a closed loop.

• Data travels in one direction (unidirectional) or both directions (bidirectional/dual ring).
• Each node acts as a repeater, boosting the signal.
• In a unidirectional ring, if one node or link fails, the entire network is disrupted.
• A dual ring provides an alternate path, improving reliability.

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4. Mesh Topology

In a Mesh topology, every node is connected to every other node via dedicated point-to-point links.

Number of Links Formula

For a fully connected Mesh network with $n$ nodes, the number of physical links required is:

$\text{Number of Links}=\frac{n(n-1)}{2}$

Example: For $n=10$ nodes: $\frac{10\times 9}{2}=45\text{ links}$

• Multiple paths exist for data — if one link fails, data is automatically rerouted.
• This makes Mesh the most reliable topology.
• However, the large number of cables makes it the most expensive and difficult to scale.

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5. Hybrid Topology

A Hybrid topology combines two or more different topologies (e.g., Star-Bus, Star-Ring, Star-Mesh).

• Used in large networks (e.g., enterprise networks, the internet) to leverage the advantages of multiple topologies.
• Example: A Star-Bus hybrid uses Star topology within each department and Bus topology to connect departments.

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Comparison Summary