Telecommunication

Network Topology

What is Network Topology?

A network topology is defined as the layout or arrangement of elements (usually nodes or links) in a communication network. Network topologies are used to define or describe the arrangement of various types of telecommunication networks – such as computer networks, command and control radio networks, and industrial field busses.

Types of Network Topology

There four main types of network topologies:

• Bus topology
• Star topology
• Mesh topology
• Ring topology

There are also hybrid network topologies, which are a combination of two or more topologies. As they are a combination of other topologies, there is a large variation in what a hybrid can look like.

The different types of network topologies are shown in the diagram below:

Selecting the right network topology depends on many factors, including the distance between each node, operational flexibility, redundancy, and the number of nodes that need to be connected to the network.

Let’s review the main types of network topologies – looking at examples and the advantages and disadvantages of each type.

Bus Network Topology

A bus topology is defined as a network that has a common backbone to connect all devices. A single cable (the backbone) works as a shared medium that devices tap or attach into via an interface connector.

Usually, bus topologies consist of two signals and ends that travel from one end to another. Bus topology is unidirectional data that are transferred from one end to another in one direction.

A diagram of a bus network has been shown below:

A device that wants to communicate with another device sends a broadcast to the wire for the other devices to see. Only the intended recipient actually processes and accepts the message. Depending on what node that needs to be connected, an RJ45 or a coaxial cable is used to connect these devices.

However, a bus network is better suited for a limited number of devices. If more than a few dozen computers are connected, the performance will drop as a result. Also, if the backbone cable fails, then the entire network becomes unstable.

Advantages of Bus Topology

The advantages of a bus topology are:

• Good for small network setups
• Less cable needed to connect the required nodes
• Gives enough flexibility to expand or reduce a network
• Cost Effective
• Easy to Understand

Disadvantages of Bus Topology

The disadvantages of bus topology are:

• Unidirectional
• If the primary cable fails, the entire network fails
• Ideal for only small networks

Star Network Topology

A star topology is defined as a network where each device is connected to a central hub via a point-to-point connection. Most home networks use this topology. This network configuration uses twisted cable; however, it can be used with fiber optic cable or coaxial cable.

A diagram of a star network has been shown below:

All data that flows through the star topology goes through a central hub before it reaches its destination. The central hub acts as a repeater to ensure that there’s zero or minimal data loss during the transmission.

Advantages of Star Topology

The advantages of a star topology are:

• Easy to install and modify
• Devices can be added, removed, or modified without slowing down the central hub.
• Less cabling needed to configure the topology
• Easy to troubleshoot
• Easy to remove parts and detect faults

Disadvantages of Star Topology

The disadvantages of a star topology are:

• If the central hub fails, all of the connected nodes are disabled
• Needs more cable length than linear topologies
• Performance is based on the hub’s efficiency, power, and configuration

Mesh Network Topology

A mesh topology can be further broken down into:

• Full Mesh Topology
• Partial Mesh Topology

Both offer an increased level of redundancy by minimizing the number of point-to-point connections between each node.

Data transmission in a mesh network is divided into two core techniques:

1. Routing
2. Flooding

Full Mesh Topology

A fully connected mesh network is defined as a network that has a point-to-point connection for every node within that network. Every device or node within a mesh network connects to other nodes in a non-hierarchical and direct manner.

A diagram of a fully connected mesh network has been shown below:

In mesh networks, the network isn’t focused on one central hub like star topology, and each node plays an active role in relaying information.

As all nodes are interconnected, this offers the maximum amount of redundancy in the case of a fault. A fully connected network also doesn’t need to use packet switching or broadcasting since there is a direct connection between every node in the network.

However, since the number of connections grows quadratically with the number of nodes, this type of setup is costly and impractical for large networks.

Partial Mesh Topology

In a partially connected network, certain nodes are connected to exactly one other node while other nodes are connected to two or more other nodes.

This makes takes advantage of some of the redundancy of a full mesh topology without the added expense and complexity required for a connection between every node in the network.

A diagram of a partial connected mesh network has been shown below:

Routing

Every node within a mesh network can have a transmission of data and routing logic for information that’s passed through the routing logic. The routing logic is used to find the shortest distance to deliver information from sender to receiver or the routing logic can be used to stop using broken lines for data transmission.

Flooding

With flooding, the same data packet is transferred to each node on the network. Therefore, no routing logic is needed in case of flooding the network. Data loss is unlikely as each node will the same data in them. This makes it fault-tolerant and robust. But, this also increases the load on the network.

Advantages of Mesh Topology

The advantages of a mesh topology are:

• High level of redundancy (robust)
• Provides privacy and security
• Fault detection and isolation are easy
• Fewer collisions and load to dedicated lines

Disadvantages of Mesh Topology

The disadvantages of a mesh topology are:

• Cost of cabling and installment are high
• Reconfiguring or installation is a long task

Ring Network Topology

A ring topology is defined as a network where every device has two neighbors for communication purposes. Every message and data package travels through a ring in a clockwise or counterclockwise direction.

A diagram of a ring network has been shown below:

In-ring topologies, all of the devices are connected in a closed loop configuration. For one data node to reach another, they have to traverse through all of the intermediate nodes. For larger networks with multiple nodes connected to a ring, repeaters are then used to stop data loss in these transmissions.

One failed device or cable destroys the loop and can break down the entire network. To make a ring network, one usually uses Token Ring, SONET, or FDDI technology. Ring topologies are usually found on school campuses or office buildings.

Advantages of Ring Topology

The advantages of ring topology are:

• Inexpensive to implement
• Better performance than bus topology and works under heavy loads
• Orderly network flow
• Makes it easier to detect faults and misconfiguration

Disadvantages of Ring Topology

The disadvantages of ring topology are:

• Adding, removing, or configuring nodes requires the network to be shut down
• One faulty node can destroy the entire network
• Transmission line failure can disrupt the network

Hybrid Network Topology

A hybrid topology (or hybrid network) is defined as two or more topologies integrated together. Hybrid technologies can be configured based on your requirements.

Hybrid topologies add more complexity, but also more flexibility to your network. Properly configured hybrid topologies are often easier to expand and scale.

Some hybrid networks include:

• Star-bus network
• Hierarchical star network
• Star-ring network
• Hybrid mesh network

Problems found in hybrid networks are easier to diagnose because the network hubs or concentration points are small and size compared to the total size of the network. The concentrated point or the hub can be fixed separately if it’s not working properly.

Hybrid networks provide increased flexibility as newer basic topologies can be added while existing ones removed. However, they will need more operational costs or higher costs to configure and maintain.

Advantages of Hybrid Topology

The advantages of hybrid topology are:

• Flexibility in design
• Potentially easier to manage
• Potentially easier to add or remove nodes
• Suitable for larger networks

Disadvantages of Hybrid Topology

The disadvantage of hybrid topology are:

• Difficult to design and maintain
• Costly