In Wireless Personal Area Networks, there are multiple topology options for forming a network of wireless nodes. The most dominant topology currently found is a star network and lately, mesh network has been gaining popularity due to multiple well defined standards coming up in the market. In this blog, we discuss about these two network topologies, their advantages and disadvantages and suitable applications for them.Star network
A star network is formed by having one central coordinator node and several peripheral nodes. All peripheral nodes can interact with the central node only and not with each other. The central node can interact with any of the peripheral nodes. The figure below shows the arrangement of a star network.
Advantages and Suitable applications
- Simple set up and configuration - the complexity of maintaining a network is pushed to the central node while other peripheral nodes only have to worry about interacting with the desired central node. This makes setting up and maintaining the network very easy.
- Power and resource efficient - In this topology, the central node is responsible for coming up with an efficient way to interact with all the peripheral nodes, thus enabling the peripheral nodes to be power and resource efficient. This allows the wireless device to have a long life even with small size. The central peripheral usually have access to large power supply and processing power, so they will be able to handle the maintenance of the network.
The simplicity of this topology has enabled it to gain popularity in lot of wireless technologies. We can see lot of star networks in our daily life. A smart phone connecting to multiple devices via Bluetooth acts as a central coordinator while other devices act as peripherals. A WiFi router in a room can be considered as central coordinator and the devices in a room connecting to the router acts as peripherals i.e. all the WiFi interactions of those devices happen with the router. This topology is perfect for following types of applications:
- Wearables and Medical devices – Theses devices usually have to interact short range with only one device – mobile or tablet. Multiple wearables have to function at the same time and have to be connected to a particular mobile/tablet. So star network becomes ideal here. This is applicable for medical devices as well which often have to monitor and report conditions of the body to a central device.
- Standalone wireless devices – These devices also need to connect to only one device usually either for some setting configuration or streaming data continuously. Example of this can be some consumer electronics like wireless speakers, camera etc. The central entity here again becomes a laptop or mobile which are power and resource abundant and can simultaneously maintain interactions with multiple devices.
While this topology is currently dominant in usage, there are certain drawbacks which make it an inefficient solution for some IoT challenges. They are:
- Short range - The biggest drawback is that the peripheral node always needs a central coordinator in the vicinity if it has to send any message. In some IoT applications, peripheral nodes are usually scattered over a large area and having a common central coordinator within range for all the peripheral nodes becomes difficult. For example, a typical Bluetooth Low Energy (BLE) device can offer range of around 10 meters in an indoor environment. If we have peripheral nodes scattered over an area of 50 square meters, then it would not be possible to have a single coordinator for all of them.
- Single point of failure - Another disadvantage is the single point of failure for the network i.e if the central coordinator goes down then the whole network becomes obsolete. This becomes a huge risk in applications where reliability has to be high.
A mesh network is formed by a group of nodes, all of which can communicate with each other irrespective of whether they are in the wireless range or not. If they are in range, they can communicate with each other directly otherwise the message can still be forwarded by the intermediate nodes from the source node to destination node. As long as each node is close to at least two other nodes, any node in the mesh can reach any other node in the mesh. The figure below show the arrangement of a mesh network.
Advantages and Suitable applications
The advantages of a mesh network are:
- Long range - messages can travel much larger distances compared to a star network. Nodes deployed over a large area can still maintain end to end communication with mesh networks as all nodes can now participate in forwarding the message. As long as each node is close to at least two other nodes, any node in the mesh can reach any other node in the mesh.
- Reliability – In mesh networks, messages can travel by multiple paths from source to destination. This makes the probability of message reaching the end point high. Thus making the network more reliable.
- Robustness - All nodes share responsibility for keeping the network alive rather than just one node taking the burden. So the network now becomes robust and has less chances of failure
With mesh networks, it is possible to implement robust wireless communication over large areas. Mesh networks are increasingly gaining importance in following applications:
- Building monitoring and control - Let’s consider we have a large room with lot of bulbs and we want to control all the bulbs wirelessly through a single switch. This can be implemented by forming a mesh network amongst all the bulbs and the switch. Upon turning on or off, the switch would transmit the message to nearby bulbs and these bulbs would again relay that message to other bulbs and then eventually all the bulbs in the room would receive the concerned message. This can be extended to any other functionality required in a large building such as heating, temperature monitoring etc. In fact, mesh networks find their usefulness in monitoring and controlling any type of assets over a large area.
- Industrial monitoring - In various industries, assets are spread over huge areas and often their functioning has to be monitored and controlled. Sensors can be deployed over a large area and mesh network can be implemented to collect and report data about the condition of assets. Covering a railway network with a mesh network to find any abnormalities in the track is a good example of this.
- Environmental monitoring – Mesh networks can be used for environmental monitoring as well. Similar to industrial environments, environmental scenarios can include forests, ponds, lakes or even agriculture fields. It is often important to monitor the health of these areas continuously. Detecting any abnormalities can avert big disasters and loss of natural resources.
Mesh networks with its advantages also brings in a complex set of challenges. They are:
- Synchronization of nodes - To ensure the messages travel instantly, all nodes in the network should have an efficient scheme of transmission and reception. Failure to do this would result in huge amounts of power wastage and since most wireless nodes are resource and power constraint, this becomes critical in the functioning of the network.
- Routing - Another challenge is designing a solution for routing the message from source to destination. The routing solution should be simple enough not to over burden the resource constraint nodes and efficient enough to keep the power consumption low. The routing solution should also take into account the maintenance of the network. It should be possible to add or remove a node without extra effort and without disturbing the functioning of the network.
Both star networks and mesh networks offer their own set of advantages along with some drawbacks. Depending on the application, usually one form of topology is more suitable than the other. Star networks are fairly simple in their topology and are useful in low power devices which have to interact with only one device in short range. Mesh networks have complex challenges and implementations compared to star networks but they offer immense advantages in applications which require monitoring assets over a large area.
In the past few years, some technologies like Thread, BLE Mesh, Zigbee have come up which address the challenges of a mesh topology. In our next blog, we will take a detailed look into mesh networking and the architecture offered by the above technologies.
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