How to sensor join gateway ?

You have to make sure all of these sensors and ember gateway use the same Zigbee profile

, fo example HA profile. If so, these sensors should be able to pair with ember gateway. By the way, these sensors might use TI CC253x but they are not manufactured by TI.

Yes ! gateway and 3 sensors use the same Zigbee profile (HA = 0x104)

And how about question 2 and 3 :

2)  I see if 3 sensor join Ember gateway, they need Trust Center Key. What is Trust Center Key of 3 sensor ?

3) What is a permissive channels of 3 sensor ?

The default TC link key of HA profile is 0x5a6967426565416c6c69616e63653039. These sensors should scan all of 16 2.4 G Zigbee channel if they follow spec.

I don't know clearly about send and receive between Sensor and Gateway (GW) :

- Step 1 : Sensor generates a link key (based on the security profile) to the TC, this is request joining

- Step 2 : GW (TC)  sends Network Key encrypted with the link key to Sensor   

- Step 3 : Sensor starts CBKE (Certificate Based Key Establishment)

- Step 4 : Sensor receives the network key, it will kick off CBKE process. 

It's right  Yikai Chen ? All this processing is auto ? 

Thank so much, Yikai Chen !

You can refer to the presentation for Zigbee security ar https://docs.zigbee.org/zigbee-docs/dcn/09-5378.pdf. All the association process is automatic.

Thanks YiKai Chen !