RE: Network Traffic Violations

[Dominique Brezinski <dom_brezinski () securecomputing com>]

At 12:01 PM 9/11/98 -0500, Rick Smith wrote:
> > At 02:41 PM 9/10/98 -0600, jrtietsort wrote:
> > > Telco-ISP's will survive because the provide the same 
> > > bandwidth to each user regardless of how many users
> > > in your area are using the service.  I think you'll
> > > find that cable modems, you are sharing bandwidth
> > > with all the other houses in your area.  
>
> Off topic, but their survival depends on their adaptability. Just about any
> practical communications infrastructure is going to share resources, so
> they're all vulnerable to degradation. For example, the telco/ISP
> combination usually suffers from a finite modem bank size. It's too soon to
> tell how much the user population must grow before typical cable modem
> performance is only 10 times faster than the telco/ISP combination. Perhaps
> the vendors will be able to scale up their infrastructure to keep customers
> happy and throughput high. Time will tell.

Wow, this is really off topic, but here is my 2 cents anyway. The
current/next generation of telco service for data connections is Digital
Subscriber Line (DSL or xDSL). DSL is the competitor to cable modems, not
standard analog modem technology. In a former life ;) I worked on
interactive TV stuff, specifically the delivery networks. How you get lots
of bandwidth to the home is a fundamental problem in the interactive TV
world, so we looked at this problem extensively. The analyst projections
showed cables modems were a short term stop gap technology and DSL was the
long term solution. The primary technical reason for this is the
scalability of the network topology. 

Cable modems use the coax network of the cable distribution plant, which is
essentially a big coax bus. There is a limited amount of bandwidth the coax
bus can provide. In order to support more users you have to do one of two
things: install more coax buses (throughout neighborhoods and into peoples
homes) or reduce the amount of bandwidth available to each customer
(degrade service). 

DSL uses the standard cat3 pair already installed in a vast majority of
homes. A DSL device connects to one end of the pair in the users home,
while the other end is connected to a line card at the central telco office
(CO). The bandwidth from the customer to CO is fixed (not shared and will
not degrade). The line card is essential an interface in an ATM switch. The
Internet connection (T1, T3, or OC-x) is connected into the ATM network.
The ATM network is the shared resource here, so in order to support more
users one of two things can be done: increase the speed of the ATM backbone
or reduce the amount of bandwidth available to each customer.

Well, it is way cheaper and easier to increase the capacity of the ATM
network at the CO or ISP than it is to install more coax throughout the
neighborhood. Market demand can be met faster and more economically without
degrading the current customer's service with DSL. Cable modems may look
attractive to some now, but in a few years....

ATM also provides better bandwidth management facilities, so your DSL
provider can give you guaranteed bandwidth if you need it and are willing
to pay for it. Cable companies just technically can't give you this level
of service.

Dominique Brezinski CISSP                   (612)628-5378
Secure Computing        http://www.securecomputing.com