Re: network topology question

[dman <dsh8290@rit.edu>]

On Thu, Feb 21, 2002 at 12:45:57AM +0100, Hans Ekbrand wrote:
 
| According to my ADSL service provider, my connection to their gateway
| is somehow "private",

This is mostly marketing-speak and quite meaningless.  They are
comparing their service with that of cable modems.  Cable modems use
some sort of bus archtecture such that most of your "connection"
(physical and link layers) is "shared" with other hosts/subnets.  ADSL
uses a dedicated piece of copper (twisted pair) between your house and
the "End Office".  The same dedicated twisted pair your analog phone
uses.  The ADSL modem just uses carrier signals of a higher frequency
than the phone, thus they can share the physical medium.  Also, DSL
uses ATM networks.  (ATM is Asynchronous Transfer Mode)  ATM is a
Virtual Circuit design, as opposed to IP's Datagram design.  Each
virtual circuit has a dedicated amount of resources allocated to it
for the lifetime of the circuit.  Of course, this circuit ends at the
end office or your isp where the IP datatgrams are extracted from the
ATM cells and routed back to the "internet".  

Here's where the intended meanings from marketing become relevant :

    o   cable modems share the same coax cable between a box in your
            neighborhood and your provider, thus is someone is using
            all the bandwidth on that line you don't get any

        The solution (that is used) :
            Limit all cable modems such that the sum of the capacities
            of all modems routing data on a given line is no more than
            the capacity of that line.  This means that you are
            "guarunteed" a certain amount of bandwidth, but you can
            never use more than it, even if no one else is using it.

    o   DSL lines are dedicated in the first place, thus you are
            guarunteed the advertised bandwidth all the time.  Of
            course, line and weather conditions can affect what the
            maximum bandwidth on the line is anyways.

    My provider claims that, as a result, DSL is more secure than a
    cable modem.  This is, obviously, bull.

    Here is an exceprt from http://www.frontier.net/about/pr050500.html
        (not the page I was looking for but contains the same information) 
    In addition to providing the highest speeds possible over copper
    wires DSL provides you a secure, dedicated connection. This means
    your DSL connection is always on. [...] This type of dedicated
    connection is a secure access using dedicated facilities and
    reliability because the network is monitored around the clock.


DSL is no more or less secure than cable because if you don't have a
firewall, you're equally vulnerable.  (even a firewall is only limited
protect, for example use IE to browse a site infected with nimbda)

-D


PS. While looking for their explanation of why DSL is secure I found
    this.  What a load of junk.

    http://frontier.custhelp.com/cgi-bin/frontier.cfg/php/enduser/std_adp.php?p_sid=NkUz-h8g&p_lva=&p_refno=000520-000009&p_created=958845848&p_sp=cF9ncmlkc29ydD0mcF9yb3dfY250PTE3JnBfc2VhcmNoX3RleHQ9RFNMIHNlY3VyaXR5JnBfc2VhcmNoX3R5cGU9MyZwX3Byb2RfbHZsMT1_YW55fiZwX3Byb2RfbHZsMj1_YW55fiZwX2NhdF9sdmwxPX5hbnl_JnBfc29ydF9ieT1kZmx0JnBfcGFnZT0x&p_li=

-- 

Many a man claims to have unfailing love,
but a faithful man who can find?
        Proverbs 20:6