OFFSET_b
0x12, 0xc0, 0x0b, 0x00, buf + OFFSET_b, SIZE_b,
down_speed = buf[OFFSET_b] | (buf[OFFSET_b + 1] << 8)
| (buf[OFFSET_b + 2] << 16) | (buf[OFFSET_b + 3] << 24);
up_speed = buf[OFFSET_b + 4] | (buf[OFFSET_b + 5] << 8)
| (buf[OFFSET_b + 6] << 16) | (buf[OFFSET_b + 7] << 24);