What this means
The IEEE assigned the MA-L block C09120 to Sichuan Tianyi Comheart Telecom Co.,LTD. Every network interface they manufacture under this block has a MAC address beginning with these digits, followed by a unique per-device identifier. If a device on your network shows a MAC starting C0:91:20, it is Sichuan Tianyi Comheart Telecom Co.,LTD hardware.