Understanding the device connection capabilities and scalability of IoT gateways is essential. This article aims to provide comprehensive answers to these common questions, enabling informed decisions for IoT projects.
When creating IoT solutions for home automation using IoT, IoT retail solutions, Industry 4.0 solutions, etc., it is necessary to understand how many devices a smart gateway can connect to ensure a reliable network and provide the required performance.
This data is crucial for budgeting and cost accounting in IoT projects, as setups with multiple endpoints may require more IoT gateways, leading to higher deployment costs. Therefore, understanding the limitations of each gateway is very important. Before answering this question, let’s first take a look at the architecture of IoT networks.
Basic IoT Network Architecture Composed of Gateway Hubs and Sub-devices
When answering the question, “How many sub-devices can a gateway connect?” it is best to first focus on the connection between perception layer devices (sub-devices) and the gateway’s central processing/edge processing functions through wireless network layer protocols.
Sensor Layer
This layer is responsible for collecting data from the environment, providing a certain level of user interaction, and implementing feedback from users or higher levels. It includes all sub-devices, such as smart sensors, smart plugs, BLE beacons, access control panels, etc. These sub-devices are usually low-power, powered by button batteries to reduce costs and simplify maintenance.
Network Layer
Sensor layer devices or IoT devices communicate wirelessly with the hub, and these wireless communication protocols constitute the network layer.
The most commonly used wireless communication protocols for interacting with endpoints are BLE, Zigbee, LoRaWAN, and Z-Wave. These low-power IoT wireless technologies save energy but have slower data transmission speeds. These speeds are acceptable for most IoT applications, such as smart homes, offices, and buildings, as sensor layer devices send data at determined time intervals rather than continuously.
However, faster wireless communication protocols like Wi-Fi are needed to connect sub-devices that require higher transmission speeds to smart hub gateways, such as cameras.
Once connected, these devices exchange data using messaging protocols such as MQTT, CoAP, and HTTP.
Data Processing Layer
This layer can be divided into two parts.
IoT Hub/Edge Processing
The gateway is the central communication device that processes endpoints in the IoT network and bridges them to the cloud in external networks (WAN). This device is responsible for edge processing and analysis and can also integrate AI processing.
The purpose is to filter out irrelevant or unavailable data before forwarding it to the cloud for analytical processing. After programming and calibration, edge computing gateways can also provide automation functions.
Cloud Analysis
With more powerful processing capabilities than gateways, the cloud can extract meaningful information from incoming sensor data, providing valuable insights to aid decision-making.
Application Layer
The application layer is the layer that interacts with users, providing a user-friendly interface to present cloud analysis and control functions that send instructions to sub-devices.
What Factors Affect the Number of Devices an IoT Gateway Can Handle?
All smart gateways can handle different numbers of sub-devices depending on the following factors.
Network Capacity and Bandwidth
Network capacity and bandwidth are closely related. Capacity refers to the speed at which data moves through the network. On the other hand, bandwidth refers to the maximum amount of data the network can handle.
IoT sub-devices with local controllers process most data locally, meaning they reduce the percentage of bandwidth consumed in the network. Therefore, gateways in such networks can handle more endpoints compared to those lacking microcontrollers.
This factor introduces another variable called throughput, which defines how much data can be successfully transmitted through the network. Therefore, if endpoints frequently send large amounts of data packets, the gateway can only process a few of these packets and confirm them.
IoT gateways have a function called channels, which refers to the communication path for transmitting data to sub-devices.
Assuming there is an 8-channel LoRaWAN gateway that can handle 1.5 million data packets per day. If each endpoint sends and receives 100 data packets per hour, the gateway can handle 1.5 million/(100×24), which equals 625 devices.
With local processing, devices may only send and receive 10 data packets per hour, allowing the gateway to handle 6250 devices.
Moreover, if the data packets or payloads are too large, the gateway must be able to create a higher bandwidth network to accommodate these devices. The more packets sent per second or minute, the higher the capacity or speed required by the network. Otherwise, the network will experience delays.
Communication Protocols
As mentioned earlier, sub-devices and gateways communicate through protocols such as ZigBee, BLE, Z-Wave, and LoRaWAN.
ZigBee is the most popular protocol for home automation, smart retail, and other similar IoT solutions, as these gateways can handle up to 65535 devices in a mesh topology. However, this protocol can only handle 21 devices in a star network and 421 devices in a tree topology.
On the other hand, a single BLE gateway can only handle 10-100 devices, but this number increases to about 320,000 devices in a mesh, which is still less than half of what ZigBee can accommodate.
Z-Wave is proprietary technology, so it is not as widespread as the other two technologies. Additionally, unlike the other two technologies, this protocol operates in a frequency band below 1GHz. These bands vary by region, ranging from 856-921MHz, and this protocol can handle a maximum of 232 devices in a small mesh network.
Although LoRaWAN is a low-power communication protocol, it allows long-distance communication, with ranges of 3 miles in urban areas and 10 miles in rural areas.
With LoRaWAN, there is no specific limit to the number of sub-devices a gateway can connect. This number depends on network capacity, bandwidth, and the processing capabilities of the network server and gateway. Some existing LoRaWAN IoT networks have tens of thousands of sub-devices connected to one gateway.
LoRaWAN uses a Time-Division Multiple Access (TDMA) scheme to manage devices, allowing efficient sharing of gateway resources among linked devices. This protocol also categorizes devices into different classes (A, B, and C), each with different requirements and modes.
Therefore, with careful planning and optimization, a large LoRaWAN network with thousands of sub-devices can be built.
Gateway and Network Server Processing Capabilities
Smarter and more powerful gateways with features like AI processing can handle more sub-devices because their bandwidth, speed, and throughput are effectively higher.
The processing capacity of the network server also determines the number of connected sub-devices. For example, the LoRaWAN network server manages the connections and registrations of sub-devices. It also ensures that endpoints effectively utilize gateway resources by scheduling data transmission time slots and distributing downlink messages to each device.
Thus, the higher the processing capabilities of these two devices, the greater the network efficiency and the more sub-devices that can be handled.
External Factors
Physical obstacles such as buildings, environmental factors like humidity and temperature, and interference from other wireless devices like Wi-Fi routers can all affect signal propagation in IoT networks. These factors can negatively impact the capacity of gateways, meaning the number of sub-devices they can connect may decrease.
Gateway Software and Firmware
Software and firmware updates make gateways operate more efficiently, meaning they can handle more devices.
Is It Better for a Gateway to Handle More Connected Devices?
We rarely find sub-devices reaching or approaching the maximum limits of a gateway in IoT networks, as these performance data are theoretical. Ideal situations do not occur in the real world due to issues like losses.
For example, LoRaWAN networks only achieve 18% efficiency when fully utilized. This means that up to 82% of the packets transmitted may be lost, or 82 out of every 100 packets may be lost. If the system includes message confirmations for endpoints, the efficiency is even lower.
On ZigBee and BLE, both operate in the crowded 2.4GHz band, and using Wi-Fi in the same space exacerbates loss issues.
Therefore, it is best to keep the number of connected devices below the maximum number a gateway can handle to maintain network performance and reliable data/packet transmission from sensors to the cloud/network server and back.
Another critical issue to consider is battery life, especially the battery life of the gateway. The more devices a gateway connects and communicates with, even using low-power protocols like ZigBee, the higher the power consumption.
Mesh networks can help shorten data paths and improve communication efficiency, but remember that all communications ultimately pass through the gateway to the cloud and back. Introducing more gateways to alleviate inbound and outbound loads is the best solution.
Conclusion
When determining the maximum number of devices assigned to a gateway, we should not consider ideal or theoretical values but look at the actual values produced due to transmission losses.
The goal is to ensure that smart IoT solutions perform better with a high level of reliability, which may involve testing each solution to determine the maximum limits that provide the best value for customers.
Source: Qianjia Network.
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