Bluetooth mesh with Bluetooth 5 and Cordio radio IP

The Bluetooth SIG's formal release of a new specification for mesh networking is big news in the Bluetooth world.  While Bluetooth technology has been around for nearly two decades it has always focused on point-to-point connections or simple broadcasting.  The SIG had not attempted to tackle the problem of mesh networking, although some companies had developed proprietary mesh protocols over Bluetooth low energy. That is, until now: By publishing a standardized mesh specification, the Bluetooth SIG aims to achieve product interoperability and a flourishing new product ecosystem for automation and the smart home. I'll explain how this mesh specification affects both SoC designers implementing Bluetooth in their chips, as well as the end users of these products, you and me. 

Mesh networking

What is mesh networking? A mesh network is network where each node can relay data to the rest of network and nodes, thus allowing multiple paths for connectivity if a node become unavailable. With mesh capabilities, a mesh network can be quite reliable, and can cover a much bigger area compared to a single node.

Bluetooth low energy mesh technology is defined by two specifications:  The Mesh Profile specification and the Mesh Model specification. 

The Mesh Profile specification defines the protocols for networking, security, and provisioning that enable device communication.  The Mesh Model specification defines the messages and data used to perform product-oriented procedures, such as scheduling a switch to turn on or dimming a light. 

Mesh uses Bluetooth low energy advertising and scanning to implement flood routing, which is simple and effective for small and medium sized networks.  Relay nodes within the network retransmit received network messages so a message can be received multiple hops away from its source.  Battery powered devices are supported through a mechanism known as friendship, which allows low power nodes to periodically wake up from sleep and check for messages.  Direct connection between a mesh network and a mobile phone is supported by transporting messages at the GATT layer over a point-to-point connection. 

Security

Security is an important feature of Bluetooth mesh, and all messages are encrypted and authenticated.  Message security is applied at both the networking layer and the application layer using different keys.  Separating application keys from network keys  allows messages to be securely relayed in the network while keeping application layer data private.  For example a mesh light won't be able to read the messages it relays to a mesh door lock. 

The Bluetooth mesh concept of group messaging is a powerful and user-friendly way to control nodes in a network.  For example a user could create a group called "living room lights" and program a switch to control that group of lights.  If another switch is added only that switch need to be programmed; if a light is replaced only that light needs to be programmed rather than the switches that control it. 

Bluetooth mesh is designed to run on top of the Bluetooth core specification 4.0 and later.  However there are certain features of Bluetooth 5 that can make Bluetooth mesh work better.  One simple feature that's new in Bluetooth 5 is called anonymous advertising.  When a device uses anonymous advertising it does not transmit its own device address in the advertising packet.  This improves privacy and also reduces power consumption, since fewer bytes are transmitted over the air. 

Another important Bluetooth 5 feature is the ability to advertise multiple sets of data concurrently.  For example, consider a mesh node that is both a proxy node and a relay node:  

  • To operate as a relay it must send mesh packets over non-connectable advertising. 
  • To allow connections as a proxy node (e.g. to a phone that connects to the mesh network via the GATT layer) it must use connectable advertising. 

Bluetooth 5 makes it possible to set up concurrent advertising for both purposesArm's Cordio-B50 stack and link layer support these Bluetooth 5 features (anonymous advertising and multiple advertising sets) and is qualified and available now.

Learn more at www.arm.com/cordio

Read more about Bluetooth SIG

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