Matter; Chip controller and OTBR communication

[alvin7]

Hi, I am very new to matter and I would like to query some doubts I had regarding the communication between the chip controller and OTBR.

1. What protocol is used? I know the chip controller and the OTBR are communicating through local WiFi/ethernet, what I want to know is the underlying protocol used for communication?
2. What is the data format send by the controller to the OTBR? 
3. What happens when we type in a 'zcl' command in the chip controller? How does it process and send the data regarding the endpoints, clusters etc to the OTBR and in turn route it to the matter device?

[AHaug]

Hi,

My colleagues in our Matter team explained it to me as follows:

1. The protocol stack used for sending Matter commands is: [15.4/WiFi/Ethernet] / IPv6 / UDP/ Matter Message
   • Communication between the controller and OTBR happens over WiFi/Etherhet and further within a Thread network over Thread/15.4.
   • Matter Message is a generic message format used for all communication initiated or received by a Matter node. For example, for messages used to establish a secure channel, and messages used to encode Matter commands.
2. Matter Message format is described in the Matter specification which we're not allowed to distribute. If you have access to the specification we can point to the specific chapter. Note that Matter Message format is used for multiple purposes and sending ZCL commands is just one of them, i.e. they use a specific Message Type in the Matter Message. ZCL commands themselves are encoded using a Matter TLV encoding which is also described in the specification.
3. When you type "zcl" command a specific ZCL command (or "action" I should have said to use Matter's nomenclature) is encoded using the Matter TLV format, then it put in a Matter Message and sent using a UDP socket. If this is the first communication with a given node, before the packet is actually sent the controller must find an IP/UDP address of the node using DNS-SD and establish a secure session with the node using Matter-specific Certificate-Authenticated Session Establishment protocol.

I hope this answers your questions!

Kind regards,
Andreas

[alvin7]

Hi, I apologize for the late reply. Thanks a lot for your response. I have a couple more queries to fill up

1. Where do i get the matter specification?
2. I want to control the matter device globally using MQTT in the border router, is there a sample code available or any documentation for said purpose?

Thank you in advance.