Operation Manual

6
1 Introduction
The one terminal device that that exploits the full potential
of ISDN, however, is the personal computer. Before,
separate terminal equipment was necessary for each
service (a fax machine to send faxes, a Vtx terminal for
Videotex, etc.). Today all that is needed is a PC, an ISDN
PC adapter and the desired application software. AVM
has played a major part in bringing about this develop-
ment to combine the power and flexibility of the personal
computer and the ISDN network. With the right ISDN
software, your computer becomes a multimedia
communications center!
1.2 USB: The Universal Serial Bus
The Universal Serial Bus (USB) transports data between
computers and peripherals at a speed of 12 Mbit/s. The
USB brings a new standard in convenience and user-
friendliness to computer hardware: with USB devices,
expanding a computer system is a simple matter of
plugging in a bus cable and installing the driver software.
USB devices all have a uniform connector.
These features make the USB an ideal platform for
connecting input and communications devices to the
computer. The new bus permits true plug-and-play and
”hot” installation, and makes it possible to connect up to
127 peripheral devices.
The USB’s architecture supports all kinds of components.
Guidelines define how different devices are allowed to
use bandwidth on the bus. The USB has a tree-shaped
topology and is regulated by a host controller. Branches
of the tree are connected by hubs; the leaf nodes are the
hardware components to be connected to the computer.
The bus cable can be up to five meters long between two
hubs or between a hub and a terminal device. Hubs can
also be incorporated in the host computer itself, or in
other USB terminal devices, such as monitors or
keyboards.
USB devices are grouped in speed classes. ”Fast devices”
access the bus at 12 Mbit/s throughput, while ”slow