The Limitations of Bluetooth Mesh

Earlier this year, we made the decision to retire SensorMesh™, a product that was built on top of the standard Bluetooth mesh framework. At first glance, Bluetooth mesh appeared to be a promising technology—serverless, open, adaptable and with an extended range compared to standard Bluetooth LE. However, as we got into its implementation and use, we found that the limitations outweighed the benefits.

Our SensorMesh™ was designed to be a versatile solution for various applications. It provided a new Bluetooth Mesh model that allowed the participation of any Bluetooth beacons or other devices without them requiring firmware updates. The system also allowed for payload filtering and time-based control to manage throughput. It was capable of transmitting data from a variety of sensors, such as location, movement, button press, temperature, humidity, air pressure, light level, open/closed status, and proximity, over the mesh network:

One of the first issues we encountered was the complicated provisioning and setup process. Unlike turnkey solutions, Bluetooth mesh required a provisioner, usually an app on a smartphone, to store encryption keys. This made the initial setup far from straightforward and ongoing management difficult.

Another significant limitation was the very low throughput, which was in the order of a few thousand bits (yes bits!) per second. For most applications, especially those requiring IoT data transmission, this was not sufficient. In many cases, using gateways proved to be a more effective solution.

The Bluetooth SIG’s chosen flooding architecture, while excellent for low latency, consumed too much power for battery-operated devices. As a result, we had to resort to installing firmware on USB dongle -style devices, which were permanently powered. This was inconvenient for many applications we saw from potential clients where mesh networks would have been ideal, such as in mines, hospitals, factories, farms and even battlefields where existing networks are already congested or non-existent.

We also found that Bluetooth GATT clients at the edge of the mesh, responsible for relaying the mesh data somewhere else, easily became congested despite the low throughput. Our workaround involved using USB dongle with mesh firmware and a COM port rather than GATT.

Bluetooth mesh offered no way to trade latency for less power consumption. Its throughput was too limited for most uses, a problem inherent to the technology. Since its announcement in 2017, Bluetooth mesh hasn’t seen many implementations outside the lighting industry. We believe this is because it was driven, designed and optimised for lighting scenarios, which require low latency and permanent power but can tolerate low throughput. Sadly, enhancements recently provided by Mesh 1.1, such as directed forwarding, device firmware update, remote provisioning and subnet bridging have come about mainly to solve problems found in Network Lighting Control (NLC).

In the end, we retired SensorMesh™ because it didn’t have a good product-market fit. The underlying characteristics of Bluetooth mesh were too limiting to make it a useful solution for the applications our customers envisioned. While Bluetooth mesh may have its niche uses, we believe its limitations make it currently unsuitable for broader applications.

Understanding Bluetooth LE Reliability

We have previously written about Bluetooth LE on the Factory Floor and Why Bluetooth LE Scanning Doesn’t Always See Devices (the First Time).

There’s a new informative paper by Martin Woolley of the Bluetooth SIG on How Bluetooth® Technology Makes Wireless Communication Reliable. It describes in detail how radio collisions, multi-path propagation, time-dispersion, transmitter-receiver synchronisation, signal strength, receiver sensitivity and buffer overflow can collude to make radio communications unreliable.

The paper explains how Bluetooth modulation schemes, CRC checks, multiple channels, coded PHY, adaptive frequency hopping, flow control and the ATT protocol work to make Bluetooth LE reliable.

The paper also takes a look how Bluetooth Mesh has been designed to achieve reliable communication.

Advanced Bluetooth on Android

Martin Woolley of the Bluetooth SIG was a recent speaker at Droidcon EMEA where he spoke about Advanced Bluetooth for Android Developers (slides).

Android Bluetooth LE Stack

Martin covered scanning, GATT, how to maximise data rates, speed vs reliability and using different PHY for enhanced range or data rates. The second part of the talk covers Bluetooth Mesh and proxy nodes.

One thing not mentioned in the slides, to be careful of, is that connection via a proxy node is relatively slow because it’s limited by the GATT connection. Proxy nodes are good for controlling (sending small amounts of data into) a Bluetooth Mesh but poor if you want to use the connected Android device as a gateway for all outgoing data.

Martin also has a blog where you can also learn about his past talks and he will be part of the new Bluetooth Developer Meetup.

Read about Beacons and the Bluetooth Mesh

Bluetooth Developer Meetup

There’s a new (virtual) Bluetooth Developer Meetup group.

Developers will share their knowledge and tell their stories of working with everybody’s favourite low power wireless communication technology

The first event will be on 15th October 2020 at 17:30 UK time (UTC+1) and will include the following speakers:

  • Jacky Cheung, Google
  • Kevin Picchi, Samsung
  • Thea Aldrich, Foundries IO
  • Martin Woolley, Bluetooth SIG

Bluetooth Market Update

The Bluetooth SIG has recently released a 2020 Bluetooth® Market Update identifying new trends and forecasts from ABI Research and other analyst firms.

The use of Bluetooth for location is expected to achieve 32% compound annual growth (CAGR):

Obviously, these and other numbers in the report were analysed prior to the coronavirus crisis.

For Bluetooth Mesh, 90% of end-product Bluetooth® mesh qualifications are lighting focused. As with the introduction of iBeacon, which initially focused on marketing messages, the wider capabilities and opportunities are initially not being fully exploited. Part of the problem is that the standard models that come with Bluetooth Mesh are more lighting focused because the standard was driven by individuals from the lighting industry.

App-based Bluetooth Mesh

Protesters in Hong Kong have been using Bluetooth mesh to communicate with one another so as to avoid using the Internet and therefore making it difficult for the Chinese authorities to intercept. However, this isn’t standard Bluetooth mesh as defined by the Bluetooth SIG. It’s a proprietary mesh protocol over standard Bluetooth.

The app used is Bridgefy and there many such peer to peer apps such as FireChat (server has been turned off and no longer works), Signal Offline and Briar that use Bluetooth and WiFi direct.

The use of stand-alone Bluetooth mesh networks isn’t limited to protesters. A growing number of SDKs allow mesh networks to used by companies and organisations. When used with iOS and Android devices (which don’t necessary have to be smartphones) these provide for WiFi-less and Internet-less communication. This allows use, for example, in emergency situations when cellular and Internet goes down. Alternatively, they can simply provide connectivity across a site where there’s no cellular coverage or WiFi.

SDKs include Bridgefy, Hype the open source android-ble-mesh, Ubudu Android Mesh, and a newer open source iOS library by Zsombor Szabo, called Berkanan SDK.

Wireshark Supports Bluetooth Mesh

Wireshark has announced support for the Bluetooth Mesh Beacon, PB-ADV, Provisioning PDU and Proxy Bluetooth mesh protocols.

Wireshark is a protocol analyser that takes packets and decodes into human readable data. It’s usually used with other hardware and software as the last stage in processing captured data. For example, you can use Wireshark with the Nordic nRF sniffer, on Adafruit hardware and on Linux.

In the case of Bluetooth mesh, data packets are encrypted. In fact, data is double encrypted in that first the data is encrypted and then the packets. This means that while you can capture packets you can only see the packet types and Bluetooth mesh metadata. You won’t be able to decrypt the actual data. It’s more useful for determining the type and size of traffic for mesh traffic optimisation.

Read about Beacons and the Bluetooth Mesh

What’s Wrong with Bluetooth Mesh?

Researchers from TU Darmstadt, Germany have a new paper Toxic Friends in Your Network: Breaking the Bluetooth Mesh Friendship Concept that looks into weaknesses in the security model underlying the Bluetooth mesh friendship mechanism.

Friendship allows a low-power IoT device to go to sleep with a separate higher-power node caching packets until the lower power device wakes up. The paper provides an overview of friendship and the Friendship Security Material(FSM) unique to this type of communication.

The researchers found three flaws in the Bluetooth friendship mechanism related to:

  • The possibility of eavesdropping on communication and selectively jamming based on size of the control messages.
  • The lack of protection of the friend security keys against an insider attack.
  • The possibility of misuse of Friend Clear messages to cause a form of denial of service attack through flattening the battery.

The paper includes a reference to tools that demonstrate these problems and discusses possible mitigations.

The Bluetooth SIG responded:

Compromise of the friendship relationship results only in a compromise of the availability of the low power node to the other nodes in the subnet.

It is the conclusion of the working group that the friendship relationship between an LPN and its friend within a mesh subnet is not intended to be secured against attack by a party already in possession of the network key.

It is the position of the Mesh Working Group and the Bluetooth SIG that neither scenario provides additional security risk for a user of the Mesh profile

In other words, the risks are appropriate to the level to which the mesh is expected to be used or attacked.

We have yet to come across any devices using friendship. Friendship is an edge case that isn’t required in most instances. Also, most existing low power devices can’t be upgraded to use mesh due to the higher memory requirement of Bluetooth Mesh.

Read about Beacons and the Bluetooth Mesh

Survey of Mesh Technologies

There’s useful new research on Wireless Mesh Networking: An IoT-Oriented Perspective Survey on Relevant Technologies by Antonio Cilfone, Luca Davoli, Laura Belli and Gianluigi Ferrari of University of Parma, Italy. It covers how various communication technologies are suitable for mesh networking.

The paper explains mesh topologies and routing protocols. It describes Bluetooth:

“BLE is presently raising more and more attention and is becoming one of the leading technologies for both IoT-oriented and industrial scenarios”

The authors provide an in-depth introduction to SIG Bluetooth Mesh. (Note that an excellent higher level overview also very recently became available from InsightSIP). The research paper also mentions other Bluetooth mesh implementations such as the draft IETF Bluetooth Mesh for IPv6.

Applications such as smart city, industrial monitoring and smart agriculture are considered and factors such as interoperability and security are mentioned. Finally, the paper compares other protocols such as Thread, ZigBee and LoRaWAN.

Read about Beacons and the Bluetooth Mesh

Bluetooth Mesh for Industrial IoT (IIoT)

There’s an informative video presentation on the Bluetooth SIG web site on Simplifying Multi-Vendor Mesh and Sensor Networks. It provides an introduction to Bluetooth mesh and explains the ways in which it can provide for Industrial IoT (IIoT).

To add to this, Bluetooth Mesh is suitable for use on the factory floor where the environment can be electrically noisy. Standard Bluetooth Mesh uses advertising on several channels rather than (GATT) connections so as to provide for more reliable communication in environments with wireless interference.

Read about Beacons in Industry and the 4th Industrial Revolution (4IR)
Read about Beacons and the Bluetooth Mesh