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When it comes to selecting the right mesh network protocols for an IoT application, one size does not fit all.
That's the reason so many protocols exist, said André Francisco, CTO and co-founder of Hype Labs, developer of a cloud-based SDK for network connectivity in Porto, Portugal.
Zigbee, Thread, Bluetooth mesh, Z-Wave -- each is a mesh networking protocol and each has unique characteristics and benefits, depending on the application and use case. But before trying to understand the protocols, it's important to consider that mesh networking is a different model of the way IoT devices connect.
"The traditional paradigm is that devices connect to a central access point, satellite or cell tower somewhere. This relies on expensive infrastructure," Francisco said. "In mesh networking, the devices, or nodes, connect directly to each other."
Therefore, instead of having an IoT node connect directly to a cell tower, which is expensive, it connects to all the other nodes on the same network. Then, when the IoT node sends content, the data hops from node to node until it either reaches the intended destination or it can find an internet exit point, Francisco said.
A mesh network topology, which can be either full or partial, increases network resilience in case of node or connection failure and generally costs less to set up than other networks, particularly over large areas.
IoT mesh network protocol options
Zigbee is a standards-based wireless technology developed to enable low-cost, low-power wireless machine-to-machine and IoT networks. Silicon Laboratories Inc. acquired Ember, one of the key contributors to the Zigbee specification, in 2012. Zigbee offers mature application layer support for home automation, lighting and metering, said Matt Maupin, senior product manager of wireless embedded systems at Silicon Labs.
The Thread protocol is a home automation wireless communication method developed, updated and managed by the Thread Group, which as hundreds of members. With Thread, IoT devices can communicate via power lines, radio frequencies or a combination of the two. Thread is the only mesh technology based on IPv6, Maupin said, which enables end-to-end routing and addressability on the same network or across networks; companies don't have to implement any additional translation layers.
Bluetooth mesh, introduced in July 2017, was designed to address the specific requirements of home, commercial and industrial networks. Bluetooth mesh devices that support Bluetooth Low Energy can provide connectivity to the cloud via a tablet or smartphone.
"This, of course, is a temporary connection, as the devices would not be able to connect to the cloud to send or receive information if the phone or tablet isn't present, requiring a gateway for an always connected experience," Maupin said.
Zigbee requires a gateway to convert and encapsulate data into IP packets, while Thread needs a border gateway because of its already existing IP-based connectivity.
Z-Wave is a mesh protocol focused on command and control in the smart home, said Johan Pedersen, product marketing manager of Z-Wave IoT at Silicon Labs, which acquired Sigma Designs' Z-Wave business in April 2018. The protocol has its own consortium, the Z-Wave Alliance, made up of 700 companies that create products and services powered by the Z-Wave technology. All the products these companies release are Z-Wave-certified.
Z-Wave is a sub-1 GHz wireless mesh network specifically developed for smart home products, such as lights, door locks, security systems and heating control.
"Sub-1 GHz means that it runs in a different frequency than Bluetooth, Wi-Fi and Zigbee," Pedersen said. "Sub-1 GHz has a longer range throughout the home than the higher-frequency ones that are typically at 2.4 GHz."
Operating in the sub-1 GHz band also helps prevent interference, he said. The 2.4 GHz band is a crowded space. With fewer devices and products on sub-1 GHz, you're less prone to wireless interference.
"You do have other technologies in sub-1 GHz," Pedersen said. "For example, Zigbee has a version that is sub-1 GHz, but there are very few products actually using it. There are tons of proprietary wireless protocols on sub-1 GHz, but not really mesh."
In the market since the early 2000s, Z-Wave is interoperable, meaning all Z-Wave devices can speak to and understand each other.
"Interoperability and backward compatibility are two key features of the Z-Wave technology," Pedersen said.
So, what about Wi-Fi? Gartner analyst Mark Hung said that very early on, Wi-Fi supported mesh networking with 802.11s; however, because there was never a certification program for it from the Wi-Fi Alliance, it was not widely implemented or adopted. But there has been a renewed effort to allow Wi-Fi to implement mesh networking, but it's not quite ready yet.
"It's even less mature than Bluetooth 5," Hung said. "I would say, though, it's early stages. Don't count Wi-Fi out just because of its install base."
How IoT mesh network protocols compare
Deciding which IoT mesh network protocols to implement depends on an enterprise's specific application or ecosystem. The size of the network, latency needed, desired throughput and overall reliability will ultimately determine which mesh networking protocol an organization selects.
From a mesh topology perspective, the protocols largely operate the same way, Hung said. Even the physical layer protocol for Zigbee and Thread is the same -- each uses the IEEE standard 802.15.4 for low-rate, wireless personal area networks. Higher in the networking stack, Hung said, is where the protocols differ, namely in how each performs in the key areas of security, throughput, power consumption, latency, scalability and IP connectivity.
However, the way Zigbee, Thread and Bluetooth mesh networks are implemented can have an effect on system performance.
"These are all designed to have low-power radios, so I can run battery-type devices, but then cover large areas through them talking to other nodes," Silicon Labs' Maupin said.
In April 2018, Silicon Labs released benchmarks for Bluetooth, Thread and Zigbee IoT mesh networks, comparing how each performed in different test conditions and network configurations. According to the benchmarks:
- In small networks under small payloads, the performance of Thread, Zigbee and Bluetooth mesh is pretty much the same.
- When payload and throughput needs increase, Thread and Zigbee outperform Bluetooth mesh. However, after it's installed, the performance of Bluetooth mesh can improve if the installer optimizes the network by manually disabling some routing nodes.
- As the size of the network increases, latency increases for all three protocols, with Bluetooth mesh experiencing the greatest increase.
- For large Bluetooth mesh networks, relay optimization can be used to optimize performance.
- Bluetooth mesh is best for short messages -- 11 bytes or less. This is especially true for multicast messages.
- Each mesh network provides standards-based support for different applications and devices.