A Beginner's Guide to IoT Wireless Connectivity

Choosing the right IoT wireless networking solution 
There are several different wireless connectivity solutions for IoT applications???? solutions. Considering the wide range of use cases, choosing the right wireless connectivity solution??? case to meet the requirements of a given IoT application can be very challenging.
　　A variety of factors should be considered when selecting a connectivity solution? solution should consider various factors such as range, data rate, security, power consumption and scalability.
　　Network topology - how sensors, actuators and gateway nodes are arranged or interconnected - is another important factor that can affect network performance.
　　The two basic architectures for IoT wireless networks are Star and mesh connections.
　　Star Topology Advantages and Disadvantages 
Star topology is shown in Figure 1.

　　Representation of the starting terrain.

　　Figure 1: Representation of the starting terrain. Image courtesy of Texas Musical Instruments The Star network consists of a central hub to which all other nodes are connected. Nodes communicate with each other through the central hub, which in most cases is also the gateway to the Internet.
　　A home Wi-Fi network is the familiar star topology, with phones, tablets, and printers all connected to a central hub (wireless access point). This central hub serves as both a router in the local network and a gateway to the Internet.
　　Since the hub is responsible for distributing data packets along the interstellar network, it can reach its destination via a single “ HOP” (data transfer between a node and the hub) or two “ hops” (data transfer between two nodes passing between the hubs) . This feature leads to fast networks with consistent and predictable performance.
　　Another advantage is that star topology-based IoT networks can easily identify and isolate a failed node because each node has a separate connection to the hub.
　　However, with packets having to pass through the central node, the network has a single point of failure. If the central node fails, the entire network will cease to exist.
　　Another major limitation of wireless stellar connectivity is that all nodes should be within direct radio range of the central node. This limits the physical size of the network.
　　In addition, stellar networks do not have the flexibility to route around RF obstacles or environments with high RF interference.
　　This is not the case for mesh networks, which typically combine multiple routing paths between every two nodes, as we will discuss shortly. Mesh networks have a more flexible layout and are more likely to be able to route around RF obstacles.
　　Mesh Networks: complete and partial mesh topologies 
In a mesh network, a node can communicate directly with multiple other nodes.
　　There are two types of mesh networks: complete and partial meshes.
　　In a complete mesh topology, each node can communicate directly with all other nodes in the network.
　　In a partial network network, shown in Figure 2, each node can connect directly to one or more nodes in the network, but not necessarily to every other node in the network.
　　Representation of a partial network mesh.

　　Figure 2: Representation of a partial network grid. Image Provided with Texas Musical Instruments IoT applications typically use a partial mesh topology to extend the scope of the network, as described below.
　　In a network network, nodes can act as repeaters to route data through the network. As a result, there are several different paths between every two nodes. This redundancy increases the resilience of the network; if one path fails, an alternative path can be used to propagate data through the network.
　　Since nodes can act as repeaters, nodes that are not in direct radio range of each other can still communicate through router nodes. This is the main advantage of mesh networks in IoT applications as it allows users to extend the range of the network beyond the range of a single radio.
　　The downside is that the multi-hop nature of the communication can increase the delay in propagating packets throughout the network.
　　Leap points are counted and, therefore, network latency is a function of the number of routers through which data packets pass. This makes evaluating network performance more complex than for simple structures such as the star topology discussed above.
　　In this case, one might use a Quality of Service (QoS) metric: the ratio of transmitted packets that reach the final destination within a specified time duration (e.g., 300ms).
　　The routing nodes of a mesh network should implement some routing algorithms to efficiently transport packets to their destinations. To implement these routing functions, the routing nodes should have more processing power and memory, which increases the complexity and cost of these nodes.
　　Zigbee Protocol for Star, Tree and Mesh Topologies 
Zigbee is an open standard designed to meet the needs of low-cost, low-power wireless IoT networks.
　　Zigbee is based on the IEEE 802.15.4 link layer and operates in unlicensed frequency bands including 2.4 GHz, 900 MHz and 868 MHz. Zigbee supports star, tree and mesh topologies.
　　A typical Zigbee network network is shown in Figure 3.
　　Zigbee network network.

　　Figure 3: An example of a Zigbee network network. Image courtesy of SM song WJ Yao The radios in a Zigbee network network play different roles. Nodes can be coordinators, routers, or endpoint devices. The coordinator sets up the network and allows routers and end devices to join the network. In addition to creating the network, the coordinator also manages the security of the network.
　　Router nodes are always listening to the information received by routing through the network. These nodes are usually mains powered.