Bluetooth Mesh - What's that noise about? (MAGAZINE)


Coming Bluetooth extensions will make the wireless technology a better fit for smart lighting, explains MAREK WIERZBICKI, while mesh extensions will retain the low power, ease of use, and reliability of the proven radio technology.


Smart lighting might be the biggest revolution the lighting industry has seen in decades, but the multitude of available wireless communication technologies can cause a real headache for manufacturers willing to delve into this new, exciting market. Bluetooth is the latest talk of the town with its mesh networking support to be adopted later this year. We at Silvair have been deeply involved in the Bluetooth Smart Mesh Working Group's efforts aimed at standardizing a Bluetooth-based mesh architecture, and this examination of the basic concepts behind one approach to a Bluetooth Mesh implementation will give you an idea as to what Bluetooth Smart mesh networking is all about.

Interested in more articles & announcements on smart lighting?

Lighting standards we've all known for years are now being challenged by the next generation of lighting systems that promise to deliver so much more than just a well-lit space. The transition toward digital lighting is happening right in front of our eyes, and while a couple of months ago many had doubts as to whether smart lighting could be a real deal, it now seems that there is no turning back. Over the last 12 months, we've seen multiple heavyweight lighting manufacturers spinning off big chunks of their traditional businesses to put more focus on connected technologies (See LEDs Magazinecoverage of Osram). Smart lighting promises new business models with a steady stream of revenue from value-added features and services, which is exactly what lighting companies need to overcome the challenges resulting from the impressive longevity of LEDs and razor-thin margins in the LED market.


Bluetooth Mesh Shows Wireless Connectivity in a Whole New Light

Many of today’s wireless platforms—especially those supported by a Bluetooth® mesh network—ensure greater flexibility and extensibility at a much lower cost than a wired system can provide.

FIG. 1. There were a number of Bluetooth-based, mesh-enabled lighting products at the Consumer Electronics Show (CES) in 2016 including a lamp from Girard Sudron and a switch from NodOn.

FIG. 1. There were a number of Bluetooth-based, mesh-enabled lighting products at the Consumer Electronics Show (CES) in 2016 including a lamp from Girard Sudron and a switch from NodOn.

Moving to networks

It is therefore not surprising that virtually every week we are hearing news about lighting manufacturers entering into agreements with companies that can relatively swiftly implement smart technologies into their products, or even straightforwardly acquiring providers of wireless connectivity, cloud services, or advanced data analytics. Things have gone so far that we've already seen Goldman Sachs downgrading its rating on one of the leading lighting manufacturers, citing concerns over the company's deteriorating earnings and emphasizing its low exposure to connected technologies. The trend is clear: Lighting systems are becoming digital, and a wide variety of smart lighting products (Fig. 1) presented at CES (Consumer Electronics Show) 2016 only confirms this.

That said, there is still no consensus regarding the wireless communication protocol that could be the go-to technology for lighting applications, let alone the entire Internet of Things (IoT). Countless times has it been said that the lack of interoperability is a major obstacle to mass adoption of connected solutions, but instead of some sort of standardization, we're only seeing things getting more and more fragmented. New technologies keep emerging, each claiming to have exactly what it takes to enable seamless, robust, and secure connectivity in the Internet of Things (IoT).

In the meantime, the more mature communication standards keep evolving to address the dynamically changing customer needs, as many of them were introduced to the market when expectations and hype surrounding the IoT and connected spaces were nowhere near as big as they are today. What's more, certain product categories did not even exist back then, with smart lighting being a perfect example of a segment that has come a long way from nonexistence to being one of the hottest smart building automation segments over just a couple of years.

One of those mature standards is Bluetooth, a wireless communication protocol that seems to have been around forever and thus enjoys unmatched brand recognition. However, for certain very specific reasons, it is currently not being considered a viable option for advanced building automation solutions. The Bluetooth Special Interest Group (SIG), a 28,000-member strong body that oversees the development of Bluetooth standards, claims this is about to change once the mesh networking support is introduced into the protocol's core specification. We are only a couple of months away from this release, so let's see what's coming.

Bluetooth Classic versus Bluetooth Smart

All that noise surrounding Bluetooth might be somewhat confusing for those not too familiar with the recent developments in the wireless communication landscape. After all, the protocol was first developed before the term "Internet of Things" was even coined. But what many are still not aware of is that the Bluetooth of today is something completely different than Bluetooth of the past.

FIG. 2. Legacy Bluetooth has relied on a hub-and-spoke topology while commercial smart lighting will require a mesh network for communications.

FIG. 2. Legacy Bluetooth has relied on a hub-and-spoke topology while commercial smart lighting will require a mesh network for communications.

The original Bluetooth, known as Bluetooth Classic, was designed as a short-range, cable-replacement technology for point-topoint communications. Initially, the main goal was to synchronize data between mobile phones, but the standard quickly became the default technology for wireless data exchange between personal computing equipment (mobile phones, PCs, PDAs) and peripherals (headsets, cordless keyboards and mice, printers, and such). Devices could form a tiny personal area network (PAN) called a piconet, whereby a single central device would coordinate the activity of up to seven active peripherals.

Fast-forward to 2010, the Bluetooth Core Specification version 4.0 is released, introducing Bluetooth Low Energy (BLE), more commonly known as Bluetooth Smart. This is where the story of Bluetooth in the IoT really begins. Bluetooth Smart was designed specifically to address the needs of a new generation of smart devices, many of which are battery-powered and therefore require fast connection times and efficient power management to reduce unnecessary energy consumption.

The new specification extended Bluetooth's usefulness to a whole new range of products, ultimately making it a default technology for all kinds of wearable devices. But despite some really outstanding features of the Bluetooth Smart radio, the protocol didn't make any significant impact in the building automation segment. Smart homes were dominated by other low-power technologies, mainly ZigBee and Z-Wave, and wireless communication never really took off in commercial spaces. Due to certain important drawbacks of the available low-power communication standards, building managers preferred to stick to wired solutions, considering them way more reliable.

The reason why Bluetooth Smart was never considered a serious contender for building automation purposes is because it was designed to support relatively simple hub-and-spoke networks (Fig. 2). Applications like smart lighting require much more than that. Peer-to-peer communication and extended range are among the must-have features enabling a robust network consisting of multiple smart bulbs, and the core specification of Bluetooth Smart simply didn't provide such capability. Its hub-and-spoke model couldn't match with the mesh topology of ZigBee or Z-Wave networks, and for this reason Bluetooth could never really compete with the two in the applications they were intended for.

Is this meshable?

Even though the support for mesh networking wasn't included in the core specification of Bluetooth Smart, several companies noticed that building a mesh network based on this particular communication standard might not be such a bad idea. In 2014, Silvair (operating as Seed Labs back then) started building a mesh architecture based on Bluetooth Smart. Transforming the protocol's single-hop topology into a robust multi-hop, peer-to-peer network was quite a challenge, but the potential reward was enormous.

A mesh network based on Bluetooth Smart also turned out to offer outstanding performance and the core features of the Bluetooth radio allowed us to overcome many of the challenges that other communication protocols have a hard time dealing with. Obviously, the technology developed by Silvair was proprietary, although we did manage to maintain compliance with Bluetooth Smart's core specification.

Having received a fair amount of input from Silvair and other companies working on their proprietary mesh solutions, the Bluetooth Special Interest Group realized that such an opportunity cannot be wasted. In February 2015, it announced the formation of the Bluetooth Smart Mesh Working Group. Its goal was to standardize mesh networking support and incorporate it into the protocol's core specification. Competing companies sat down to share their experiences and find the best way to implement the mesh architecture into Bluetooth Smart. Near the end of 2015, the SIG officially confirmed that it's on track with the development of the Bluetooth Mesh, and that the standard would be adopted at some point in 2016. Moreover, some major improvements with regard to both the data rate and range of Bluetooth Smart will be included in the new standard.

The standardized mesh architecture based on Bluetooth Smart is shaping up to be a powerful framework enabling robust and scalable implementations in some of the most challenging applications. Being part of that development process and seeing many of our concepts being incorporated into the global standard is a great feeling. We are currently among the leading contributors to the Bluetooth Smart Mesh Working Group. The details about the upcoming mesh standard remain strictly confidential until some official announcements are made by the SIG itself, but we can provide you with a sneak peek into the basic concepts behind our Silvair Mesh technology, which might give you a good idea of what Bluetooth-based mesh networking is all about.

Meet a mesh

Silvair Mesh has been developed to allow users to build their smart mesh networks in which one or more mobile devices (smartphones/tablets) can control one or more mesh-enabled peripheral devices (e.g., lamps, sensors, dimmers, switches, etc.). When equipped with the mesh software stack, essentially an enhanced Bluetooth Smart stack, these devices can communicate with each other and the central controller via the Bluetooth Smart radio using the protocol's standard mechanisms called GATT (Generic Attribute Profile). This means that all mesh-enabled peripherals can create their own autonomous mesh network that does not require any central device to operate.

FIG. 3. Smart mesh capabilities are added to Bluetooth devices in the network, transport, and application layers in software and don't impact the physical and link layers that are captured in radio ICs and modules.

FIG. 3. Smart mesh capabilities are added to Bluetooth devices in the network, transport, and application layers in software and don't impact the physical and link layers that are captured in radio ICs and modules.

The decision to base Silvair Mesh on Bluetooth Smart was intentional, as it meant that the ecosystem would be compatible with all existing Bluetooth Smart devices and chipsets. However, a mesh stack also requires numerous additional features to standard Bluetooth Smart. For instance, the Silvair Mesh includes a high-performance Bluetooth controller and a new Network Security Manager, as well as the secure OverThe-Air Update functionality, which means that a device can be upgraded to the newest version of the firmware at any time.

Such a carefully crafted mesh software stack can be installed on any compatible Bluetooth chip. Silvair also developed a reference design for modules to provide the best possible solution for large installations such as those found in commercial buildings. These modules consist of standard Texas Instruments CC254x Bluetooth modules with upgraded firmware, an amplifier, and an antenna. Operating at +10-dBm Tx (transmit) power and with -98-dBm Rx (receive) sensitivity, the modules provide a 108-dB link budget that translates to a range of 1500 ft (about 500m) in the open air. Inside buildings, this value will obviously be much lower and dependent on numerous factors, yet it still remains impressive.

An important thing to realize is that mesh is a purely software solution. This means that Bluetooth Smart chipsets found in today's smartphones can control devices employing proprietary technologies such as Silvair Mesh, and will remain perfectly suitable for controlling and managing mesh networks once the standard is adopted by the SIG. The aforementioned software stack is applied to the networking and application layers of the standard Bluetooth Smart protocol stack as shown in Fig. 3.

How the mesh works

Now let's consider how the mesh extension works. There are two types of communication within a Silvair Mesh network: central to peripheral and peripheral to peripheral. Once the mesh network is commissioned, there is no need for further central-peripheral communication.

Central devices are usually smartphones and tablets. Such devices would typically run some type of control software. In the Silvair case, we developed an app for iOS and Android devices. The central devices are used to configure and manage the network but can also perform a software update of peripheral devices. Central devices connect to peripherals using Bluetooth Smart's standard GATT services. While this type of connection is fully compatible with Bluetooth 4.0, it employs certain proprietary techniques to allow many smartphones to be used simultaneously to control more than eight peripheral devices with eight being the limit in standard Bluetooth 4.0.

Peripheral devices are the nodes of a mesh network. A robust mesh implementation must allow peripherals to talk to each other and act as relays that pass messages through the mesh. This is a radical departure from the original architecture of Bluetooth Smart, and it allows for controlling entire groups of devices using multicast (one to many) communications - e.g., dimming a group of ceiling lights in a hallway. The Silvair Mesh implementation allows a maximum of 63 hops, which enables it to cover very extensive areas out of the box, in contrast to other technologies that require setting up more complicated or more expensive networks.

One of the most significant concepts introduced in the Silvair implementation is connectionless communication, which means that every peripheral can advertise its status in the network. As a result, lights, fans, shades, and any other mesh-enabled device are displayed automatically in the app on the central device, not only as a simple list of available devices, but with very specific parameters that can be controlled by the user - e.g., on/off, color, temperature, fan speed, or shade position. Every status change made by the user is immediately advertised to the network, and every controlling device in the mesh is updated instantly with the new status.

Network setup

As will be required in commercial applications, the Silvair Mesh software allows networks of any size to be set up, but the way in which large and small networks are commissioned, is different. Small networks of up to about 30 devices can be commissioned and managed using just the app on a smartphone or a tablet. The plug-and-play nature of Bluetooth, and the fact that the protocol is natively supported by virtually all smartphones and tablets on the market, makes the entire process extremely simple and intuitive. The app detects and displays mesh devices in its vicinity. The user creates a mesh network by selecting which devices should be added, and by giving the network a name. Once added to the network, associations and relationships can be set up between the devices as desired. The smartphone can then be switched off and these connections will remain in place (Fig. 4).

FIG. 4. Silvair Mesh supports both smaller mesh networks controlled by a single smartphone and complex networks with dedicated cloud-connected servers.

FIG. 4. Silvair Mesh supports both smaller mesh networks controlled by a single smartphone and complex networks with dedicated cloud-connected servers.

Networks of over about 30 devices, or the ones requiring more sophisticated associations, scenarios, and network monitoring services, are best set up using some type of server or management appliance. In the case of Silvair, an embedded server called Silvair Logic hosts all the logic that controls the entire network, checks the status of all peripherals, and reports any issues and unusual events via a browser-based interface.

Other mesh needs

There are a few other key elements of a Bluetooth Mesh implementation that we will mention briefly here. There needs to be a concept of permissions for control devices that ensures proper management of devices in the network. The Silvair software stack implements four levels of permissions: 1) Administrator - can operate all devices within the network, as well as configure them and manage other users' permissions; 2) Family - can operate all devices within the network, but cannot configure or manage them; 3) Guest - has limited permission to operate selected devices within the network; 4) and AdHoc - can operate public devices only on a one-to-one basis (no access to the mesh network).

Likewise, the network nodes or peripherals require the ability to provide information on their operational status and programmability. The Silvair software stack defines three Peripheral Device States: 1) Factory Default - the device leaves the factory in this state and is ready for commissioning; 2) Private - all communication is encrypted, so only users with matching keys can decrypt the state information and control the device; and 3) Public - state information, as well as selected control functions, are not encrypted and can be accessed by anyone.

The Bluetooth difference

The question one might ask at this point is why the Bluetooth Smart mesh would be any better than other mesh protocols available on the market? Simply put, it's all about the radio. Out of all low-power, low-bandwidth communication standards, none is even close to having such impressive qualities as Bluetooth Smart. This allows the protocol to address some of the most difficult issues in such challenging applications as smart lighting, where multicast, synchronous operation and responsiveness are among the must-have features.

We've tested many other technologies inside out, and we know exactly why the existing mesh protocols have failed to deliver the smart lighting experience to environments where reliability and scalability are top priorities. And we firmly believe that this year's adoption of the Bluetooth Smart mesh standard might finally open the door for smart lighting networks to become widely deployed in professional applications.

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Bluetooth mesh networking, conceived in 2015,[1] adopted on July 13, 2017[2] is a protocol based upon Bluetooth Low Energy that allows for many-to-many communication over Bluetooth radio.

It has been defined in Mesh Profile Specification[3] and Mesh Model Specification.[4]


Communication is carried in the messages that may be up to 384 bytes long, when using Segmentation and Reassembly (SAR) mechanism, but most of the messages fit in one segment, that is 11 bytes. Each message starts with an opcode, which may be a single byte (for special messages), 2 bytes (for standard messages), or 3 bytes (for vendor-specific messages).

Every message has a source and a destination address, determining which devices process messages. Devices publish messages to destinations which can be single things / groups of things / everything.

Each message has a sequence number that protects the network against replay attacks.

Each message is encrypted and authenticated. Two keys are used to secure messages: (1) network keys – allocated to a single mesh network, (2) application keys – specific for a given application functionality, e.g. turning the light on vs reconfiguring the light.

Messages have a time to live (TTL). Each time message is received and retransmitted, TTL is decremented which limits the number of "hops", eliminating endless loops.

Bluetooth Mesh is a flood network. It's based on the nodes relaying the messages: every relay node that receives a network packet that authenticates against a known network key that is not in message cache, that has a TTL ≥ 2 can be retransmitted with TTL = TTL - 1. Message cache used to prevent relaying messages recently seen.

Bluetooth Mesh has a layered architecture, with multiple layers as below.

Model LayerIt defines a standard way to exchange application specific messages. For example, a Light Lightness Model defines an interoperable way to control lightness. There are mandatory models, called Foundation Models, defining states and messages needed to manage a mesh network.
Access LayerIt defines mechanism to ensure that data is transmitted and received in the right context of a model and its associated application keys.
Upper Transport LayerIt defines authenticated encryption of access layer packets using an application (or device specific key). It also defines some control messages to manage Friendship or to notify the behavior of node using Heartbeat messages.
Lower Transport LayerThis layer defines a reliable (through a Block Acknowledgement) Segmented transmission upper layer packets, when a complete upper layer packet can't be carried in a single network layer packet. It also defines a mechanism to reassemble segments on the receiver.
Network LayerThis layer defines how transport packets are addressed over network to one or more nodes. It defines relay functionality for forwarding messages by a relay node to extended the range. It handles the network layer authenticated encryption using network key.
Bearer LayerIt defines how the network packets are exchanged between nodes. Mesh Profile Specification defines BLE advert bearer and BLE GATT bearer. Mesh Profile defines Proxy Protocol, through which mesh packets can be exchanged via other bearers like TCP/IP.

Theoretical limits[edit]

It's yet to be determined what are the practical limits of Bluetooth Mesh technology. There are some limits that are built into the specification, though:

Limit for a networkValueRemarks
Maximum number of nodes32 767The limit is 32768 addresses and while a node may occupy more than one address, practical limit is most likely lower
Maximum number of groups16 384

Number of virtual groups is 2128.

Maximum number of scenes65 535
Maximum number of subnets4 096
Maximum TTL127

Mesh models[edit]

As of version 1.0 of Bluetooth Mesh specification, the following standard models and model groups have been defined:

Foundation models[edit]

Foundation models have been defined in the core specification. Two of them are mandatory for all mesh nodes.

  • Configuration Server (mandatory)
  • Configuration Client
  • Health Server (mandatory)
  • Health Client

Generic models[edit]

  • Generic OnOff Server, used to represent devices that do not fit any of the model descriptions defined but support the generic properties of On/Off
  • Generic Level Server, keeping the state of an element in a 16-bit signed integer
  • Generic Default Transition Time Server, used to represent a default transition time for a variety of devices
  • Generic Power OnOff Server & Generic Power OnOff Setup Server, used to represent devices that do not fit any of the model descriptions but support the generic properties of On/Off
  • Generic Power Level Server & Generic Power Level Setup Server, including a Generic Power Actual state, a Generic Power Last state, a Generic Power Default state and a Generic Power Range state
  • Generic Battery Server, representing a set of four values representing the state of a battery
  • Generic Location Server & Generic Location Setup Server, representing location information of an element, either global (Lat/Lon) or local
  • Generic User/Admin/Manufacturer/Client Property Server, representing any value to be stored by an element
  • Generic OnOff Client & Generic Level Client
  • Generic Default Transition Time Client
  • Generic Power OnOff Client & Generic Power Level Client
  • Generic Battery Client
  • Generic Location Client
  • Generic Property Client


  • Sensor Server & Sensor Setup Server, representing a sensor device. Sensor device may be configured to return a measured value periodically or on request; measurement period (cadence) may be configured to be fixed or to change, so that more important value range is being reported faster.
  • Sensor Client

Time and scenes[edit]

  • Time Server & Time Setup Server, allowing for time synchronization in mesh network
  • Scene Server & Scene Setup Server, allowing for up to 65535 scenes to be configured and recalled when needed.
  • Scheduler Server & Scheduler Setup Server
  • Time Client, Scene Client & Scheduler Client


  • Light Lightness Server & Light Lightness Setup Server, representing a dimmable light source
  • Light CTL Server, Light CTL Temperature Server & Light CTL Setup Server, representing a CCT or "tunable white" light source
  • Light HSL Server, Light HSL Hue Server, Light HSL Saturation Server & Light HSL Setup Server, representing a light source based on Hue, Saturation, Lightness color representation
  • Light xyL Server & Light xyL Setup Server, representing a light source based on modified CIE xyY color space.
  • Light LC (Lightness Control) Server & Light LC Setup Server, representing a light control device, able to control Light Lightness model using an occupancy sensor and ambient light sensor. It may be used for light control scenarios like Auto-On, Auto-Off and/or Daylight Harvesting.
  • Light Lightness Client, Light CTL Client, Light HSL Client, Light xyL Client & Light LC Client


Provisioning is a process of installing the device into a network. It is a mandatory step to build a Bluetooth Mesh network.

In the provisioning process, a provisioner securely distributes a network key and a unique address space for a device. Provisioning protocol uses P256 Elliptic Curve Diffie-HellmanKey Exchange to create a temporary key to encrypt network key and other information. This provides security from a passive eavesdropper. It also provides various authentication mechanisms to protect network information, from an active eavesdropper who uses Man-In-The-Middle attack, during provisioning process.

A key unique to a device known as "Device Key" is derived from elliptic curve shared secret on provisioner and device during the provisioning process. This device key is used by the provisioner to encrypt messages for that specific device.

Terminology used in Bluetooth mesh networking specification[edit]

  • Destination: The address to which a message is sent.
  • Element: An addressable entity within a device.
  • Model: Standardized operation of typical user scenarios.
  • Node: A provisioned device.
  • Provisioner: A node that can add a device to a mesh network.
  • Relay: A node able to retransmit messages.
  • Source: The address from which a message is sent.

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