Hello, the general non-invasive machine interface is connected to the position where the machine air outlet and the pipeline are connected. Most of them use three-way pipes, which have the advantages of uniform oxygen mixing and less oxygen loss. Several of them are connected to the mask, and the nasal oxygen tube is directly inserted into the oxygen port of the mask. Most invasive machines are connected near the air inlet. Because invasive machines need more accurate oxygen concentration, they generally need machines to measure the proportion of mixed oxygen, so oxygen must be connected at the air inlet. I'm a product engineer of respiratory health company. Please contact me again if you have any questions. I hope I can help you.