A number of different Cable Modem configurations are possible. These three
configurations are the main products we see now. Over time more systems will arrive.
External Cable Modem
The external Cable Modem is the small external box that connect to your
computer normally through an ordinary Ethernet connection. The downside is that you need
to add a (cheap) Ethernet card to your computer before you can connect the Cable Modem. A
plus is that you can connect more computers to the Ethernet. Also the Cable Modem works
with most operating systems and hardware platforms, including Mac, UNIX, laptop computers
etc.
Another interface for external Cable Modems is USB, which has the
advantage of installing much faster (something that matters, because the cable operators
are normally sending technicians out to install each and every Cable Modem). The downside
is that you can only connect one PC to a USB based Cable Modem.
Internal Cable Modem
The internal Cable Modem is typically a PCI bus add-in card for a PC. That
might be the cheapest implementation possible, but it has a number of drawbacks. First
problem is that it can only be used in desktop PC's. Mac's and laptops are possible, but
require a different design. Second problem is that the cable connector is not galvanic
isolated from AC mains. This may pose a problem in some CATV networks, requiring a more
expensive upgrade of the network installations. Some countries and/or CATV networks may
not be able to use internal cable modems at all for technical and/or regulatory reasons.
Interactive Set-Top Box
The interactive set-top box is really a cable modem in disguise. The
primary function of the set-top box is to provide more TV channels on the same limited
number of frequencies. This is possible with the use of digital television encoding (DVB).
An interactive set-top box provides a return channel - often through the ordinary plain
old telephone system (POTS) - that allows the user access to web-browsing, email etc.
directly on the TV screen.
cable-modems.org
