Network Topology: Types, Diagrams, and Definition

What is a Network Topology?

A network topology describes how nodes and links are arranged. Physical topology maps actual devices and media. Logical topology describes how data flows, which may differ from the physical connections. The concept applies to computer networks, radio systems and industrial field buses.

Types of Network Topology

There four main types of network topologies:

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

Point-to-point, tree, line and hybrid arrangements are also common. A hybrid combines topology patterns, so its actual structure must be shown rather than inferred from the label.

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

Select topology by node count and distance, media, capacity, delay, redundancy, failure domains, security, management, expansion and cost. Physical and logical topology should be assessed separately.

The following sections describe common patterns and their conditional advantages and disadvantages.

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.

In a physical bus, nodes share one backbone medium. Signals may propagate along the bus in both directions even when a particular access protocol controls transmission order or data flow.

A diagram of a bus network has been shown below:

On a shared-medium bus, every attached interface may observe a transmitted frame, while addressing identifies the intended recipient. Cable, connector, impedance and termination depend on the network standard; RJ45 and coaxial cable are not interchangeable choices based only on the node.

Bus capacity and supported node count depend on the protocol, cable and segment limits. A break, poor termination or connector fault can disrupt part or all of a shared segment.

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:

• Shared medium can create contention and fault propagation
• 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 connects to a central hub through a point-to-point connection. Common in home networks, this setup typically uses twisted cables, but fiber optic cables or coaxial cables can also be used.

A diagram of a star network has been shown below:

Traffic between edge nodes passes through the central device. An Ethernet hub repeats signals, while a switch forwards frames selectively. Neither device guarantees zero data loss.

Advantages of Star Topology

The advantages of a star topology are:

• Easy to install and modify
• One edge link can often change without interrupting other edge links
• Dedicated links make faults easier to isolate
• 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
• Central-device capacity, configuration and availability limit the network
  

Mesh Network Topology

A mesh topology can be further broken down into:

• Full Mesh Topology
• Partial Mesh Topology

A full mesh maximises direct point-to-point links. A partial mesh uses fewer links and may retain alternate paths for selected nodes.

Two mechanisms often discussed with routed mesh networks are:

1. Routing
2. Flooding

Full Mesh Topology

A fully connected mesh network is defined as a network where each node has a point-to-point connection with every other node. This non-hierarchical setup ensures direct communication between all nodes.
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.

A full mesh provides a direct link for every node pair, so one link failure does not remove all connectivity between that pair when another route is usable. It can still use packet switching, routing and control-message flooding.

A full mesh with n nodes needs n(n – 1) / 2 undirected links. Cabling, interfaces, routing state and control traffic therefore grow quickly as nodes are added.

Partial Mesh Topology

In a partial mesh, some node pairs have direct links and others communicate through intermediate nodes. No rule requires any node to have exactly one neighbour.

This can provide alternate paths where they matter without the link count of a full mesh. Resilience depends on the chosen paths and routing behaviour.

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

Routing

Routing selects a path from source to destination using topology information, metrics and policy. A routing protocol can update paths after a link failure, but convergence is not instantaneous and the chosen path is not always the physically shortest.

Flooding

Flooding forwards a packet or control update across multiple links so reachable nodes receive it. Implementations need duplicate suppression, scope or other controls. Flooding does not prevent loss, and redundant transmission increases bandwidth and processing load.

Advantages of Mesh Topology

The advantages of a mesh topology are:

• High level of redundancy (robust)
• Can provide alternate paths between selected nodes
• 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

In a simple physical ring, each node connects to two neighbours and the links form a closed loop. A protocol may send traffic in one direction, both directions or over a protected counter-rotating path.

A diagram of a ring network has been shown below:

Traffic follows the ring between source and destination, passing intermediate nodes or switching equipment as the implementation requires. Regeneration, reach and node limits come from the network standard, not from ring shape alone.

A single break can interrupt an unprotected ring. Dual rings, bypass mechanisms or rapid protection switching can restore a path. Token Ring and FDDI are historical examples, while optical transport systems still use ring protection.

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:

• Some ring implementations interrupt service when nodes are added, removed or reconfigured
• 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

Troubleshooting a hybrid requires an accurate diagram of physical links, logical paths, addressing and failure domains. Concentration points can simplify isolation, but they can also create bottlenecks or shared failure points.

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 disadvantages of hybrid topology are:

• Difficult to design and maintain
• Costly