Kramer Electronics 648 - Manual (Page 5)

Overview
3
3.2 About the FireWire Repeater
Many computers today come with one or more FireWire ports on the rear
panel. These ports let you attach many devices to your computer quickly and
easily. The operating system also supports FireWire, so the installation of the
device drivers is quick and simple.
Connecting a FireWire device to a computer is easy – you just plug it into the
port. If it is an uninstalled FireWire device, the operating system auto-detects
it and installs software support for it automatically. If the device has already
been installed, the computer activates it and starts talking to it.
You plug the hub into your computer, and then plug your devices (or other
hubs) into the hub. By chaining hubs together, you can build up to 63
available FireWire ports on a single computer.
A FireWire repeater has bi-directional signals. The standard defines FireWire
as a Peer-to-Peer connection; that is why two devices, or a device and a
computer can talk to each other.
It is important to note that everything depends on your computer’s software,
and the firmware of the devices. Sometimes, it is possible that a computer can
work with many FireWire devices simultaneously (like a distribution
amplifier), sometimes it can work with many devices in time-sharing mode
(like a switcher). But most often it is possible to work one-to-one. In this case,
you have to disconnect all the devices that are unnecessary at this time and
leave only two of them. Since FireWire is a hot-plug standard, you can
connect/disconnect devices at any time.
Repeaters can be powered or unpowered. The FireWire standard lets devices
draw their power from their FireWire connection. Obviously, a high-power
device, like a professional DV camcorder, will have its own power supply, but
low-power devices like a Webcam derive their power from the bus in order to
simplify them. The power for this (up to 1.5 amps at 12 volts) comes from the
computer.
If you have several self-powered devices, then your repeater does not need to
be powered, as none of the devices connecting to the repeater needs additional
power, and the repeater itself can derive power from the computer. If you have
many unpowered devices, you probably need a powered repeater.