Bluetooth mesh networking

Bluetooth Mesh is a computer mesh networking standard based on Bluetooth Low Energy that allows for many-to-many communication over Bluetooth radio. The Bluetooth Mesh specifications were defined in the Mesh Profile[1] and Mesh Model[2] specifications by the Bluetooth Special Interest Group (Bluetooth SIG). Bluetooth Mesh was conceived in 2014[3] and adopted on July 13, 2017 (2017-07-13).[4]

Bluetooth mesh networking
Developed byBluetooth SIG
IntroducedJuly 13, 2017 (2017-07-13)
IndustryLighting, IoT
Physical range100-1000 meters (depending on mesh relaying configuration)

Overview

Bluetooth Mesh is a mesh networking standard that operates on a flood network principle. 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 caching is used to prevent relaying messages recently seen.

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.

Architecture

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

Bluetooth mesh profile
Layer Functionality
Model Layer It 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 Layer It defines mechanism to ensure that data is transmitted and received in the right context of a model and its associated application keys.
Upper Transport Layer It 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 Layer This 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 Layer This 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 Layer It 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.

Topology

Nodes that support the various features can be formed into a mesh network.

Bluetooth mesh profile
Feature Functionality
Relay receive and retransmit mesh messages over the advertising bearer

to enable larger networks.

Proxy help a node supporting the Low Power feature to operate by storing

messages destined for those nodes.

Low Power receive and retransmit mesh messages between GATT and

advertising bearers.

Friend operate within a mesh network at significantly reduced receiver

duty cycles only in conjunction with a node supporting the Friend feature.

Theoretical limits

The practical limits of Bluetooth Mesh technology are unknown. Some limits that are built into the specification include:

Limit for a network Value Remarks
Maximum number of nodes 32 767 The limit is 32768 addresses and while a node may occupy more than one address, the practical limit is most likely lower.
Maximum number of groups 16 384

Number of virtual groups is 2128.
Maximum number of scenes 65 535
Maximum number of subnets 4 096
Maximum TTL 127

Mesh models

As of version 1.0 of Bluetooth Mesh specification,[2] the following standard models and model groups have been defined:

Foundation models

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
  • 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

Sensors
  • 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
  • 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

Lighting
  • 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

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-Hellman Key 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.

Security of provisioning process has been analyzed in a paper presented during IEEE CNS 2018 conference.[5]

The provisioning can be performed using a Bluetooth GATT connection or advertising using the specific bearer.[1]

Terminology used in the Bluetooth Mesh Model and Mesh Profile specifications
  • 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.

Implementations

Approved ("qualified") by Bluetooth SIG
Bluetooth mesh implementations approved ("qualified") by Bluetooth SIG
Name Submitter Qualification date QDID Type
Bluetooth Stack for Embedded Systems - MESH profile[6] Silvair, Inc. July 18, 2017 98880 Profile Subsystem
Qualcomm Bluetooth Mesh[7] Qualcomm Technologies International, Ltd. July 18, 2017 98856 Profile Subsystem
Silvair Mesh Models[8] Silvair, Inc. July 26, 2017 99282 Profile Subsystem
Wireless Gecko Mesh Profile[9] Silicon Laboratories September 21, 2017 101318 Profile Subsystem
CYW-MESH 1.0[10] Cypress Semiconductor Corporation October 3, 2017 101726 Component (Tested)
Qualcomm Bluetooth Mesh Model[11] Qualcomm Technologies International, Ltd. October 20, 2017 102243 Profile Subsystem
EtherMind Bluetooth Protocol Stack, 5.0 (Single Mode) + Mesh[12] Mindtree Limited January 24, 2018 106544 Component (Tested)
Telink SIG Mesh SDK[13] Telink Semiconductor February 1, 2018 106546 Profile Subsystem
TOSHIBA Bluetooth_stack_mesh-1[14] Toshiba Corporation February 13, 2018 104143 Component (Tested)
AMICCOM Mesh Profile[15] AMICCOM Electronics Corporation March 14, 2018 109370 Profile Subsystem
Amiccom Bluetooth Mesh Model[16] AMICCOM Electronics Corporation March 30, 2018 110168 Profile Subsystem
Airoha SIG mesh[17] Airoha Technology Corp. April 2, 2018 110202 Profile Subsystem
Marvell Mesh stack v1.0[18] Marvell Technology Group April 27, 2018 110569 Component (Tested)
nRF5 SDK for Mesh [19] Nordic Semiconductor May 2, 2018 111537 Profile Subsystem
Realtek Bluetooth 5 Mesh Solution[20] Realsil Microelectronics Inc July 27, 2018 115668 Profile Subsystem
STSW-BNRG-Mesh[21] STMicroelectronics August 2, 2018 116029 Profile Subsystem
RDA BT Host 5.0[22] RDA Microelectronics, Inc. September 13, 2018 115860 Profile Subsystem
JYMC-MESH-1[23] Shanghai Frequen Microelectronics Co., Ltd. October 10, 2018 119229 End Product
RW-BLE-MESH[24] CEVA, Inc. October 31, 2018 119268 Component (Tested)
ARM Ltd Cordio Mesh[25] ARM Ltd December 11, 2018 116593 Profile Subsystem
Samsung SLSI Bluetooth Mesh[26] Samsung Electronics Co., Ltd. December 21, 2018 122442 Profile Subsystem
Bluelet Host Stack V12[27] Barrot Technology Limited December 25, 2018 123056 Component (Tested)
ESP BLE Mesh v0.6[28] Espressif Systems (Shanghai) Pte. Ltd. January 14, 2019 124137 Profile Subsystem
BK3435 BLE Core Spec 5.0 with MESH[29] Beken Corp March 12, 2019 127926 End Product
Actions Mesh Profile Subsystem[30] Actions (Zhuhai) Technology Co., Limited March 21, 2019 127646 Profile Subsystem
AliOS Things BLE host and mesh profile v2.1.0[31] Alibaba (China) Co., Ltd. April 19, 2019 129750 Host Subsystem
Tonly SIG Mesh Stack[32] Shenzhen Tonli Science and Technology Development Co.,Ltd May 5, 2019 130160 Profile Subsystem
Sino Wealth IBLE SIG Mesh Profile[33] Sino Wealth Electronic Ltd. June 18, 2019 133403 Profile Subsystem
Qualcomm Bluetooth Mesh and Mesh Model v4.0[34] Qualcomm Technologies International, Ltd. June 19, 2019 128410 Profile Subsystem
PAN1020 Mesh Profile subsystem[35] Shanghai Panchip Microelectronics Co., Ltd July 1, 2019 129291 Profile Subsystem
Apache NimBLE BLE Host including BLE Mesh[36] JUUL Labs, Inc. July 15, 2019 131934 Component (Tested)
Tmall mesh Stack[37] Alibaba (China) Co., Ltd. July 20, 2019 128246 Profile Subsystem
ClarinoxBlue[38] Clarinox Technologies Pty Ltd August 2, 2019 134454 Host Subsystem
BlueX Mesh[39] BlueX Microelectronics Corp Ltd. August 20, 2019 137436 Profile Subsystem
Zephyr OS Mesh[40] The Linux Foundation September 20, 2019 139259 Profile Subsystem
WCH Bluetooth Mesh[41] Nanjing Qinheng Microelectronics Co., Ltd. June 1, 2020 144808 Profile Subsystem

Free and open-source software implementations

Free software and open source software implementations include the following:

  • The official (included in Linux kernel by Linus Torvalds in 2001[42]) Linux Bluetooth protocol stack BlueZ, dual free-licensed under the GPL[43] and the LGPL,[44] supports Mesh Profile, from release version 5.47,[45] by providing meshctl tool to configure mesh devices. BlueZ was approved as a "qualified" software package by Bluetooth SIG in 2005.[46] BlueZ is not considered to be a qualified Bluetooth Mesh stack as Bluetooth Mesh is not listed as a supported profile.
  • Apache Mynewt NimBLE, free-licensed under the Apache License 2.0,[47] supports Bluetooth Mesh from release version 1.2.0.[48] It was qualified on July 15, 2019 (2019-07-15) with QDID 131934.[36]
  • Zephyr OS Mesh, free-licensed under the Apache License 2.0,[49] supports Bluetooth Mesh from release version 1.9.0.[50] Zephyr OS Mesh 1.14.x was qualified on September 20, 2019 (2019-09-20) with QDID 139259.[36]

References
  1. "Mesh Profile Bluetooth® Specification" (PDF download). Bluetooth Technology Website. 2017-07-13. Retrieved 2017-07-18.
  2. "Mesh Model Bluetooth® Specification" (PDF download). Bluetooth Technology Website. 2017-07-13. Retrieved 2017-07-18.
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