What this means

The IEEE assigned the MA-S block 70B3D5913 to Shenzhen Riitek Technology 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 70:B3:D5:91:3, it is Shenzhen Riitek Technology Co.,Ltd hardware.