How to understand the data linker layer and physical layer in the Mesh network?

RE: How to understand the data linker layer and physical layer in the Mesh network?

lgs — Thu, 16 Dec 2021 16:35:32 GMT

Hi,

Thanks. Basically, They are working between multi-node.

Regards,

Gaosheng

RE: How to understand the data linker layer and physical layer in the Mesh network?

tesc — Thu, 16 Dec 2021 13:37:57 GMT

Hi,

There are mechanisms in Bluetooth mesh for acknowledging messages, so that a sender is aware that a message has been received by the recipient. There are also parameters that can be set on the various nodes, related to message sending and relaying, for balancing throughput, reliability, etc of the network.

Bluetooth mesh is the best choice when there are small and infrequent messages intended for multiple recipients in a network of changing topology. If your throughput requirements are high, and the communication is over a fixed network from one node to another, then there might be other options that are better suited for your use case, such as a network based on BLE connections.

Regards,
Terje

RE: How to understand the data linker layer and physical layer in the Mesh network?

lgs — Thu, 16 Dec 2021 12:49:54 GMT

[quote userid="8164" url="~/f/nordic-q-a/79391/how-to-understand-the-data-linker-layer-and-physical-layer-in-the-mesh-network/343851#343851"] I am not familiar with "control functions", can you elaborate a bit on what you mean?[/quote]

Hi,

I mean some functions like in the transport layer in the TCP/IP model. It can establish a reliable connection between nodes.

With best regards,

Gaosheng

RE: How to understand the data linker layer and physical layer in the Mesh network?

tesc — Thu, 16 Dec 2021 10:49:32 GMT

Hi,

1. The bearer layer is the bottom layer of the Bluetooth mesh stack, below the Network layer. Basically it is the very thin layer that you need, for Network PDUs to be transported over either BLE advertisemens (using specific advertising types for the advertising data) or in a BLE connection (using a specific GATT service). See the Mesh profile specification v1.0.1 section 3.3 Bearers for the details of the bearer layer.

2. The bearer gets a Network PDU from the network layer. The Network PDU is described in the Mesh profile specification v1.0.1 section 3.4.4 Network PDU.

3. Bluetooth mesh is a managed flooding network. Packets propagate through the network through relay nodes, who resend the message up to the TTL number of jumps. There is no routing, as in a routed network.

4. I am not familiar with "control functions", can you elaborate a bit on what you mean?

Regards,
Terje

RE: How to understand the data linker layer and physical layer in the Mesh network?

lgs — Thu, 09 Dec 2021 23:47:01 GMT

Hi Terje,

I am looking back for a further question.

1. I am still confused about the "bearer" layer. I am still not sure of its functions. For example, is it if including some parts of the network layer, and some parts of the linker layer.

2. When a packet transmits to the bearer, is it a "datagram" like in the network layer?

3. Does the network layer have routing functions?

4. Does the transport layer have control functions?

With best regards,

Gaosheng

RE: How to understand the data linker layer and physical layer in the Mesh network?

tesc — Thu, 16 Sep 2021 11:15:37 GMT

Hi,

If you are looking for the advertising packet itself, then the mesh stack uses its own implementation (it does not use the SoftDevice for that.) The data structure is packet_t found in packet.h. There is a folder <sdk_root>/mesh/bearer/src where all the source files for the bearer layer can be found. If, at any point, you see SoftDevice API calls, then the code performed by the SoftDevice is closed source and not something we share. The mesh stack part of things, however, are all to be found under <sdk_root>/mesh/

Regards,
Terje

RE: How to understand the data linker layer and physical layer in the Mesh network?

lgs — Mon, 13 Sep 2021 08:51:58 GMT

Hi Terje,

Can you help me? I have an emergency. How can I get the source code of the data linker layer?

Regards,

Gaosheng Liu

RE: How to understand the data linker layer and physical layer in the Mesh network?

lgs — Thu, 09 Sep 2021 16:03:41 GMT

Hi Terje,

Nice for your reply. Actually, I want to construct the frame format in the data linker layer by myself.

So, I need to know the data linker layer.

Regards,

Gaosheng Liu

RE: How to understand the data linker layer and physical layer in the Mesh network?

tesc — Thu, 09 Sep 2021 15:02:53 GMT

Hi,

Few (if any) network specifications follow the OSI model completely, and Bluetooth mesh is no exception. What corresponds to the data link layer from the OSI model would be a combination of the bearer layer, some of the underlying BLE specification, and maybe even some of the network layer.

The bearer layer consists of two options for bearer: BLE advertisements (ADV bearer) and BLE connections (GATT bearer). The format used follows the Bluetooth specification for those options. Changing this may be difficult, in particular the GATT bearer which uses the precompiled BLE stack (that we call "SoftDevice") which cannot be altered.

Further, changing any part of the Bluetooth mesh stack will void the qualification.

What is the purpose of changing anything in the bearer layer? Maybe there are other ways to achieve the same goal.

Regards,
Terje