This read-create value identifies the interface a BUS will forward traffic over, which must equal a value of ifIndex in the ifTable, referring to the physical ATM port rather than a logical layer on top of it, and it can only be set at row creation and not altered afterward. Because it's locked at creation time, moving a BUS to a different physical interface later requires deleting and recreating the row entirely rather than simply changing this value. If the BUS needs to move to a different ATM port, say during a hardware replacement, the admin must delete the existing busStatus row and create a new one with the new ifIndex.