As any other 1394 device, bus analyzers rely on a dual stage approach for its bus interface, i.e. physical layer device (PHY) and a link layer controller (LLC). Especially the PHY is normally realized as a standard off‐the‐shelf component. So when used within a test instrument this device will participate like any other device in the tree/identification process and therefore change the bus wide device enumeration. An example for this is shown in the left hand graphics (click to enlarge). Notice how the bus enumeration changes when the additional device (for this argumentation an analyzer) is added to the bus.