What is Network Topology? Beginners Crash Course

While network geography attempts to describe the scale of a network, network topology describes the organization of how data moves from host to host.

And so, if you are maintaining or building a network, understanding network topology is a foundational skill which can help increase your demand as an IT professional.

In this article, we learn what network topology is & some common examples. If you need a refresher on network basics, make sure to read my article on important network concepts.

What is network topology?

Network topology is the organization of how data, moves from one host to another host. It is used to describe the arrangement of different devices in a network.

Network topology considerations
• Wired and wireless standards
• Total number of users
• Location of users
• Location of servers & network equipment

When we talk about network topology, we are either talking about physical or logical topology. Since there are some important differences, we will briefly discuss them.

Logical topology

A logical topology describes the how the network traffic actually flows. It is not concerned with the physical layout of the network, only with how the data flows.

• Traffic/Signal flow
• Usually associated with the Data Link layer, of OSI model

For example, in the logical diagram below, there is no reference to the actual location of any of the network components. This is because a logical topology isn’t concerned with how the network will physically look.

Physical topology

A physical topology describes how the network is actually connected. Such as the actual wires and connections of network devices. Physical topology takes into consideration the physical characteristics of the environment, as well as the network devices.

• How nodes are connected
• Location of nodes
• Physical layer of OSI model

Now that we better understand the difference between a logical & physical topology, let’s have a look at some commonly used networks.

Bus

Let’s start by learning about the bus topology. In this layout, every host is connected to a single bus. The “bus” was often just a chunk of wire that each host connected to, and was often referred to as the trunk, or backbone.

In a bus configuration such as the one depicted above, the cable was terminated at both ends to prevent interference from signals reflecting back.

• Single cable running through an area – all data transmitted thru this cable
• Devices “tap” into the cable via T-connector or vampire tap
• Single collision domain
• Single point of failure
• Older technology, not frequently used

Ring

Now, let’s have a look at the ring topology. In a ring topology, all the nodes are connected together in a physical ring, or circle. For this reason, there is no cable termination, each node re-transmits the data until it reaches the correct destination.

• Single cable running in a circle, or ring
• Data travels in a single direction
• Token Rings used to avoid collisions
• Each host is a peer, there is no need for a server
• Single point of failure
FDDI Ring

FDDI Ring, also known as Fiber Distributed Data Interface, uses two rings and as a result, provides some redundancy. Modern ring networks are usually FDDI networks.

Star

The star topology is the most popular physical LAN topology, on account of the simple design. In a star topology every device, or node, is connected to a single point. However, as a result, this central point can become a bandwidth bottleneck.

• Most popular LAN topology
• Devices connected to single point
• Single point of failure

Star bus

This topology is considered hybrid, since it combines two different topologies – the star & the bus topologies.

Mesh

When each host is interconnected, this is considered a fully-meshed topology. For that reason, this is considered the most redundant topology. As a result of each node being interconnected, the cost and complexity increases quickly as more nodes are added to the network.

In fact, you can easily calculate the number of connections using this formula:  x = n(n-1)/2

• Mostly logical topology
• Every node is connected to each other
• Highly redundant
• Critical networks may use this topology
• Impractical for very large networks

Wrap up

As we have seen, networks can be arranged in many different physical or logical ways. From highly interconnected & redundant networks like full-mesh, to basic networks such as the bus topology, networks take many different forms. Hopefully this blog post has makes it easy to understand some of the most common network topologies.

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Categorized as Beginner