You could, perhaps, be forgiven for characterizing the situation with IoT protocols as semi-chaotic, with competing systems jostling for market share. In a way, it’s reminiscent of the Fieldbus wars, which went on from the late 1980s to about 2000.
Like any communication system, IoT is organized in layers, with (often several competing) protocols/standards at each layer. The model most people know best may be the seven-layer Open Systems Interconnect (OSI) model. Starting at the bottom, it comprises Physical (PHY), Datalink, Network, Session, Presentation and Application layers.
The TCP/IP model has just four layers, several of them subsuming multiple OSI layers. The TCP/IP stack consists of the network access layer, which combines the OSI PHY and Datalink layers; the Internet layer, corresponding to the OSI Network layer; the Transport layer, corresponding to the OSI Transport layer; and the Application layer, which combines the OSI Session, Presentation, and Application layers.
This article will take a look at some of the competing wireless protocols used in putting together IoT systems.
Network topologies
Star networks
A star network uses a central hub that communicates with other satellite nodes; all communications pass through the hub, which controls all network functions and acts as a repeater. A star network can be wired (Ethernet is an example) or wireless (e.g., Wi-Fi)
Mesh networks
In a mesh network, each node is connected to its nearest neighbors; messages between two widely-separated nodes are passed from node to node until they reach their destination. A mesh is self-organizing and self-configured, which makes installation simple, and are self-healing, which makes them robust. If one node goes down the traffic that would have gone through it is automatically re-routed through other nodes.
Datalink layer — wireless
Let’s look at some standards that extend down to the Datalink layer (including the PHY and MAC layers in the OSI model). Remember that most of them also define higher layers to form a complete system. Both short-range and long-range systems are available.
Fair warning: while information on maximum data rate is published, it’s important to remember that such a number may have been measured under ideal conditions. As commercials say, “Your results may vary.”
Short range, low data rate
We’ll begin with low data rate (≤1 Mbps) wireless systems, although some versions of what were originally low data-rate protocols have considerably great capabilities; Bluetooth 3.0 + HS is an example. Most of these are battery-operated, with years of battery life.
One of the best-known is ZigBee, which can be configured in star, mesh and hybrid topologies. Its data rate is given as 250 kbps, although this may not always be the case. There are several variations and spin-offs of ZigBee. ZigBee IP is similar to regular ZigBee, but uses Internet Protocol version 6 (IPv6) technology for mesh networks, and offers scalable architecture and improved security. It’s aimed at remote control and sensing applications. ZigBee Pro adds enhancements like the ability to accommodate larger networks and network hops as well as improved routing. ZigBee Smart Energy v2.0 is a version of ZigBee with enhancements (especially regarding the ZigBee IP network layer) and is intended for household energy and water management applications.
Bluetooth is also ubiquitous, perhaps most frequently for linking cell phones to headsets. Available in several classes with differing power levels, it uses a master-slave architecture. Range, depending on class, is from 0.5 to about 100 meters. Bluetooth is available in a range of profiles; here are some of the best known.
Bluetooth 1.2 has a data rate of up to 721 kbps. Bluetooth 2.0 +EDR and Bluetooth 2.1 +EDR (enhanced data rate) have a maximum data rate of 2.1 to 3 Mbps. Bluetooth 3.0 +HS (High Speed) has a theoretical maximum data rate of up to 24 Mbps, using a separate Wi-Fi (802.11) link. Bluetooth 4.0 +LE (Bluetooth Low Energy, BLE or Bluetooth Smart) uses a client/server architecture and has a range of up to 100 m and an over-the-air data throughput of 125 kbps, 1 Mbps or 2 Mbps. Bluetooth 4.2, aimed specifically at IoT applications, has a data rate of about 1 Mbps. Bluetooth 5.0 offers better battery life than 4.2 and can reach up to 200 or 400 m (outdoors) with a data rate of up to 2 Mbps. It also has better security control.
Z-Wave, aimed primarily at home automation, uses mesh topology with a gateway that acts as a network controller and connection to the outside world. The data rate is 9.4 or 60 kbps, and point-to-point range is up to 30 m (line-of-sight), less in buildings. Since it uses a mesh topology, a working network can be considerably more spread out.
Thread, which was created specifically for IoT in the home, uses 6LoWPAN and mesh-based 802.15.4 PHY. It can handle 250 to 300 devices and stated data rate is 250 kbps.
Short range, higher data rate (>1 Mbps)
Probably the best-known of the short-range high data rate protocols is Wi-Fi (aka Wireless Ethernet or 802.11), which has a range of about 50 m, uses a star topology and offers typical data rates of 150 to 200 Mbps. Newer versions, based on 802.11-ac, may reach 500 Mbps to 1 Gbps.
Long range, low power, low data rate (LPWAN)
Long-range, low-power, low-data-rate, ultra narrowband protocols with ranges up to several km include Sigfox, LoRaWAN, Telsensa, Nwave, Weightless and NB-Fi. We will discuss only the first two.
Sigfox has a range of 30 to 50 km in open areas and 3 to 10 km in congested ones. The data rate is 10 to 1000 bps.
LoRaWAN bears many similarities to the preceding, but is not strictly ultra narrow band, because it uses chirp spread spectrum technology, as do Haystack Technologies and Symphony Link. The data rate is 300 bps to 50 kbps, and the range is up to 15 km in open areas and 2 to 5 km in built-up areas.
WANs: Long range, high speed, more power
Cellular technology has, in theory, unlimited range, as it connects to the worldwide telephone system; in reality, practical range is up to 200 km. It requires too much power for use in remote battery-operated devices. Depending on the technology used, data rates range from less than 199 kbps to 10 Mbps.
WiMAX, which stands for Worldwide Interoperability for Microwave Access, is defined by IEEE 802.16. Originally intended by the WiMAX Forum to be used for “the delivery of last mile wireless broadband access as an alternative to cable and DSL,” it lost one of its primary markets when major carriers adopted LTE but it is finding increasing use in IoT applications. The latest version claims a maximum data rate of 1 Gbps, 70 Mbps — or in some cases 30 to 40 Mbps — at 35 to 50 km (yes, that kilometers). The current version is WiMAX 2.0, and an LTE-compatible version called WiMAX Advanced is in the works.
