====== IoT Network Topologies ======
IoT networks are structured networks in which nodes are organised according to a defined hierarchy. An IoT network topology is a given arrangement or configuration of IoT devices to form an IoT network. 
IoT network topology refers to the structural layout of devices (nodes) in an IoT network, shaping how devices communicate and how data flows between them. The choice of topology significantly impacts the network’s performance, reliability, scalability, and cost. Below is an expanded discussion of fundamental IoT network topologies, their attributes, advantages, challenges, and use cases.

**1. Star Topology**
<figure netstar>
{{ :en:iot-reloaded:network_topologies-star.png?300 |Star Topology}}
<caption>Star Topology</caption>
</figure>

In a star topology (figure {{ref>netstar}}), all devices are connected directly to a central hub or gateway, the network’s communication and coordination point. The nodes are within the radio propagation of the gateway. Thus, they can communicate directly with the gateway, but if a node is out of the propagation or coverage range of the gateway, it is cut off from the network. 

**Advantages**

  * Simplicity: Straightforward design makes implementation and maintenance easier.
  * Failure Isolation: If a device fails, it does not affect other devices in the network.
  * Ease of Management: Centralised communication simplifies monitoring and troubleshooting.
  * Low Latency: Direct communication with the hub reduces delays in data transmission.

**Disadvantages**

  * Single Point of Failure: The entire network is disrupted if the central hub fails.
  * Scalability Limits: The central hub can become a bottleneck as the number of devices increases.
  * Distance Constraints: Communication is limited by the maximum range between devices and the hub.

**Use Cases**

  * Home Automation: Smart lighting, thermostats, and security cameras communicating with a central hub.
  * Agricultural Monitoring: Sensors reporting soil and weather conditions to a centralised gateway.

**2. Tree Topology**
<figure nettree>
{{ :en:iot-reloaded:network_topologies-tree.png?400 | Tree Topology}}
<caption>Tree Topology</caption>
</figure>
Tree topology (figure {{ref>nettree}}) organises devices hierarchically, with a root node at the top and subsequent devices forming branches at multiple levels. It is a structured extension of the star topology. In this type of topology, some nodes operate as relays for others. If one of the relays fails (crashes or experiences poor link quality), all the descendant nodes that depend on it will be disconnected from the network. \\
There is a particular case of the tree-of-trees topology available (among others in Bluetooth) called Scatternet.

**Advantages**

  * Scalability: Devices can be added at any level of the hierarchy, making it suitable for large networks.
  * Organised Data Flow: Hierarchical design facilitates efficient routing and data aggregation. 
  * Distributed Processing: Intermediate nodes can process data locally, reducing load on the root node.

**Disadvantages**

  * Higher-level Dependency: Failure at higher levels can disconnect entire branches of the network.
  * Complex Setup: Requires careful planning and configuration to optimise performance.
  * Maintenance Challenges: Troubleshooting issues in large tree networks can be time-consuming.

**Use Cases**

  * Smart Cities: Streetlights and traffic systems are organised hierarchically.
  * Industrial IoT: Layered monitoring systems for production lines or warehouses.

**3. Mesh Topology**
<figure netmesh>
{{ :en:iot-reloaded:network_topologies-mesh.png?400 |Mesh Topology}}
<caption>Mesh Topology</caption>
</figure>
In a mesh topology (figure {{ref>netmesh}}), each device is interconnected with one or more devices, creating multiple communication paths. Mesh networks can be partial (some nodes connected) or full (all nodes interconnected). It extends the tree topology by adding redundant paths. Each node in the network has at least two neighbours to which the packet can be transmitted. Therefore, if some nodes fail, the multi-hop networks or the traffic flow will not be interrupted. 

**Advantages**

  * High Reliability: Multiple paths ensure communication continues even if some nodes fail.
  * Self-healing: Dynamic rerouting of data enhances robustness and fault tolerance.
  * Scalability: New devices can be added without significant reconfiguration.
  * Optimal Coverage: Mesh topology can extend communication over large areas.

**Disadvantages**

  * High Complexity: Implementation and management are challenging, especially in entire mesh networks.
  * Energy-intensive: Devices in the network require more power for constant communication and data forwarding.
  * Higher Costs: Increased hardware requirements for maintaining multiple connections.

**Use Cases**

  * Smart Grids: Power distribution systems with redundancy.
  * Disaster Recovery: Emergency communication networks in affected areas.
  * Industrial IoT: Critical systems requiring fail-safe communication.

**4. Linear Topologies**
<figure netlinear>
{{ :en:iot-reloaded:network_topologies-linear.png?400 |Linear Topology}}
<caption>Linear Topology</caption>
</figure>
Linear topology (figure {{ref>netlinear}}) connects devices sequentially, with each node linked to its immediate neighbour.

**Advantages**

  * Simplicity: Straightforward and cost-effective to set up.
  * Geographic Suitability: Ideal for applications aligned linearly, such as pipelines or conveyor belts.
  * Ease of Expansion: New devices can be added to the ends without disrupting the network.

**Disadvantages**

  * Single Point of Failure: Failure of any device or connection affects all downstream nodes.
  * Latency: Data travels through intermediate nodes, increasing transmission times.
  * Limited Scalability: Long networks can experience signal degradation.

**Use Cases**

  * Infrastructure Monitoring: Pipeline integrity, railway tracks, or highways.
  * Agriculture: Sequential monitoring of irrigation systems or crop fields.

**5. Bus Topology**
<figure netbus>
{{ :en:iot-reloaded:network_topologies-bus.png?400 |Bus Topology}}
<caption>Bus Topology</caption>
</figure>
In a bus topology (figure {{ref>netbus}}), all devices share a common communication backbone, and data is broadcast across the bus.

**Advantages**

  * Cost-effectiveness: Minimal cabling requirements reduce deployment costs.
  * Easy Implementation: Straightforward setup and operation.
  * Low Data Collision: Suitable for small networks with limited activity.

**Disadvantages**

  * Backbone Dependency: Failure of the main communication bus disrupts the network.
  * Performance Limitations: Adding more devices increases collision risk and reduces efficiency.
  * Troubleshooting Challenges: Identifying and resolving faults in the backbone can be difficult.

**Use Cases**

  * Temporary Monitoring Systems: Event monitoring or short-term projects.
  * Small IoT Deployments: Basic automation in homes or small businesses.

**6. Ring Topology**
<figure netring>
{{ :en:iot-reloaded:network_topologies-ring.png?320 |Ring Topology}}
<caption>Ring Topology</caption>
</figure>
Ring topology (figure {{ref>netring}}) arranges devices in a closed loop, where data travels around the ring in one or both directions.

**Advantages**

  * Consistent Performance: Equal access to the network ensures reliable data transmission.
  * Fault Tolerance: Bidirectional communication prevents disruption in case of a single failure.
  * Predictable Data Flow: Ensures orderly and systematic communication.

**Disadvantages**

  * Failure Sensitivity: A single point of failure can disrupt unidirectional rings.
  * Latency: Larger rings result in longer transmission times.
  * Inflexibility: Adding or removing nodes requires reconfiguration.

**Use Cases**

  * Industrial Automation: Networks in factories or assembly lines.
  * Sensor Arrays: Environmental monitoring in circular layouts like greenhouses.

**7. Hybrid Topology**
<figure nethybrid>
{{ :en:iot-reloaded:network_topologies-hybrid.png?400 |Hybrid Topology}}
<caption>Hybrid Topology</caption>
</figure>
Hybrid topology (figure {{ref>nethybrid}}) combines elements of multiple topologies to create a customised network that leverages their strengths and minimises weaknesses.

**Advantages**

  * Flexibility: Adaptable to a wide range of applications and environments.
  * Scalability: Supports growth by integrating different topologies as needed.
  * Resilience: Combines the reliability of mesh or tree structures with the simplicity of star or bus designs.

**Disadvantages**

  * Complexity: Design and configuration are challenging due to heterogeneous components.
  * High Costs: Increased hardware and implementation expenses.
  * Integration Issues: Ensuring smooth communication between different topologies can be difficult.

**Use Cases**

  * Smart Cities: Integrating smart homes, traffic systems, and utility monitoring into a unified network.
  * Industrial IoT: Complex systems requiring multiple topology types for optimal performance.

Choosing the proper IoT network topology requires carefully evaluating the application’s needs, including reliability, scalability, cost, and energy efficiency. Often, IoT deployments use a combination of topologies to optimise performance across diverse requirements. Understanding each topology’s strengths and limitations is essential for designing effective IoT networks.