You are essentially correct, the ethernet signal is routed to converter such
as a QUAM64 modulator, which produces a 27mbps wide RF band for
the data signal. There is a limit as to the number of users that can share
this RF trunk based on number of drops and distance. So from any give head
end there will be numerous trunks or channels. There are numerous methods
to produce the connectivity; two way RF, asymetrical RF, or telco return,
all of which are determined by the cable co's physical cable plant in your area.
>From a security point of view, a cable company would rather control the
Quality Of Service (your speed vs. your cost) rather than the content. However
for business users this is a different story, whereas a more managed service
as far as access/restriction is concerned will most likely be employed.
The RF return unit such as the LanCity/Baynetworks, Motorola is an always
on device both upstream and downstream. Telco return units such as 3com
are only considered on after a successful dial up logon.
In order for a cable co to make cable modems attractive to the masses the
prices must be competitive with the analog modem ISP's cost to the consumers
while the service/speed is above ISDN/aDSL. While cable modems appeal to
power users, it is only through the mass markets will this project survive.
Subject: Re: cable modem security
Author: <dlang @
Date: 3/16/98 2:53 PM
Cable Modems are BUS technology, you are sharing the bandwidth with everyone
If you think of the cable as 10base2 ethernet cable you will have the right
"Michael H. Warfield" <mhw @
Date: Mon, 16 Mar 1998 15:36:29 -0500 (EST)
Marc Handelman enscribed thusly:
> I have been told by @Home folks that you are on a WAN with this box.
> Make sure you have file sharing and printer sharing off. Any other security
> issues that are evident in NT are still there. In addition, you could run a
> personal firewall product to limit all ports of entry...
I can partially confirm this. Another individual at the Atlanta
Unix Users Group noticed that his cable modem box "blinked" even when
he was "not on". He put his ethernet interface in promiscuous mode and
was able to "sniff" the cable!
This may vary with cable company and physical distribution plant,
but assume that you are WIDE OPEN AND EXPOSED on a cable modem! Your
neighbors can, theoretically, sniff your traffic, pictures, pages, URL's
E-Mail, etc, etc, etc...
> -----Original Message-----
> From: Ned Kelly <Ned .
> To: firewalls @
COM <firewalls @
> Date: Saturday, March 14, 1998 8:23 PM
> Subject: cable modem security
> >I have just installed a cable modem from the @home network to a single
> >machine running NT 4.0 SP3. It provides REALLY GREAT performance, but I
> >cannot get any support from @home about security.
> >I only plan to run Netscape, and read mail and news groups. What can I do
> >to protect data on this machine from security risks?
I agree with the second poster's comments about a personal firewall.
That and unbind netbios from TCP/IP. Oh! And be sure to keep those hotfixes
up to date... :-) Boy... Teardrop sure woke a lot of folks up...
> >Ned Kelly
> >Senior Engineer
> >Computer Innovations Inc
> >PH 732 345 1250
> >FAX 732 345 1237
Michael H. Warfield | (770) 985-6132 | mhw @
(The Mad Wizard) | (770) 925-8248 | http://www.wittsend.com/mhw/
NIC whois: MHW9 | An optimist believes we live in the best of all
PGP Key: 0xDF1DD471 | possible worlds. A pessimist is sure of it!