Bluetooth Mesh
There are many reasons to convince us that the Bluetooth mesh network will be the most successful low-power IoT standard.
Its 1.0 version has greatly exceeded everyone's expectations. It has all the basics, including an extremely deep and flexible application layer (see mesh model and mesh device property specifications for details). It will change the way we communicate around things. Before we do, let's first look at what makes this new global technology so revolutionary.
Bluetooth mesh involves many novel and unique concepts, but its main asset lies in the data packet, which is also a differentiating factor. It is very compact and this compactness helps ensure the spectral efficiency and throughput of the Bluetooth mesh network.
Into the packet
Bluetooth mesh is the first wireless standard to meet the huge expectations of the Internet of Things.
Radio is a shared medium, and conflict is one of the main problems it needs to solve. This is simple: shorter packets will mean fewer conflicts. But how short can it be? The answer is in the mesh configuration file specification section 3.4.4: up to 29 bytes.
Of course, such a design starts with the basics: a compressed binary payload, not a textual representation. Covering a wide range of use cases (including interconnected lighting, building automation, and sensors), the 11 bytes of the application payload also look right. The opcode is 1-2 bytes and the parameter is up to 10 bytes. The parameters include the measured value of the sensor or multi-dimensional illumination (brightness, hue, saturation) with conversion time.
Safety and control
In addition, there are two projects that may be considered as additional but necessary burdens: addressing/transmission control (SRC, DST, CTL + TTL: 5 bytes total) and security (IVI + NID, SEQ, AppMIC, and NetMIC).
IVI + NID is 1 byte. This byte helps identify the network (is this a network that I know and has a key to interact with?). SEQ is a unique concept of 3 bytes, along with a slowly transmitted IV index, forming a 7-byte long serial number. Each packet sent on the mesh network has a unique sequence number based on the given SRC address. The intelligence here is that the air interface packet contains only 3 bytes. The remaining 4 bytes change slowly and are known by the network.
The necessity of the sequence is reflected in two aspects: detecting relay packets (very small security attacks) and being a key component of current networks and applications - see section 3.8.5 of the above specifications.
Information integrity check
The MIC (Message Integrity Check) defines the security level of the system. The Bluetooth mesh network has two layers of security protection - the network layer and the application layer. Messages can be protected by two separate keys. This is useful for relay nodes, allowing them to authenticate messages at the network layer, but cannot tamper with the application payload. A light bulb that relays information to the door lock cannot change the payload from open to closed, and only checks if the packet belongs to its own network.
The network layer MIC can be 8 or 4 bytes long. When it is in a shorter form, it is combined with the application layer MIC and can still be 8 or 4 bytes long. The end result is an application's payload with robust security and flexible addressing capabilities that are sufficient for almost all building automation, lighting control and sensor applications.
And all of this exists in a very compact form factor. Combined with the modulation scheme provided by Bluetooth Low Energy, it is also "light as a swallow" and includes all necessary radio interface fields such as preamble, access address and CRC for a total of 47 octets. Section. As a result, a single transmission time on a single frequency is less than 400 μs. Compared to other current wireless technologies, it takes 10 times less time to transmit similar messages. This advantage can be doubled when using the new 2M PHY introduced with Bluetooth 5.
Spectral efficiency
The success of any wireless system depends fundamentally on spectrum efficiency. It's like the success of a passenger plane depends on its fuel efficiency. When it comes to low-power, ultra-short messages, etc., Bluetooth mesh is an order of magnitude stronger than other wireless solutions. In terms of data transmission, this is the first wireless standard to meet the great expectations of the Internet of Things era.
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