Each USB network requires a so-called USB host (or "master") to which the USB devices (or "slaves" or "clients") are connected. The USB host is usually a computer and is equipped with a A type USB connector.

Devices are typically equipped with B type USB connectors and A-to-B cable(s) are used to connect the USB device(s) to the host. It's not possible to connect only "slaves" among each other via B-to-B cables (e.g. one cannot connect an USB mouse to an USB printer because the supervising host is missing).

In the meantime even stand-alone Midi-USB hosts are available (e.g. by Kenton) and some devices with type B connector also offer host functionality. Please refer to the user manual of the unit in question. All products from Doepfer with USB interface are devices (e.g. Dark Energy, Dark Time, Dark Link, all A-100 modules with USB interface, all keyboards).