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RE: TEST [7:41824] posted 04/18/2002
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Heck no, if we where we would not be checking e-mail.

-----Original Message-----
From: Gibson, Darrin [mailto:darrin.gibson@xxxxxxxxxxxxxxx]
Sent: Thursday, April 18, 2002 9:43 AM
To: cisco@xxxxxxxxxxxxxx
Subject: TEST [7:41824]


Is the group working?

-----Original Message-----
From: bergenpeak [mailto:bergenpeak@xxxxxxxxxxxxx]
Sent: Tuesday, March 19, 2002 8:54 AM
To: cisco@xxxxxxxxxxxxxx
Subject: Re: Is cable network really a shared medium? [7:38705]


Hi Sam,

The shared vs non-shared issue DSL providers mention is somewhat
misleading.   In any residential cable or DSL network, you will
have stat muxing.   In a cable network, this happens on the HFC
network.  In a DSL network, this happens at the Agg router (the
one that terminates all of those DSL connections).   The Internet
is one big stat mux.  In either the DSL or Cable approach, the 
customer observed performance will be a result of many factors,
including access network design (how many subs share the cable
or agg router), the behaviors of these other users, the regional
network design, the size and types of peering connections, and
where the users are actually surfing too.  

My house has a long driveway that only I use.  Does that mean
I'll get to work faster than the neighbors down the street
which live in an apartment complex and share a driveway with
other folks?

In both approaches, one can prioritize traffic or partition bandwidth
to certain groups of users.

The current standard for how IP/ethernet frames are transmitted over
an HFC network is defined via the DOCSIS 1.0 spec.  This specification
is available at www.cablelabs.com.   This spec defines how to
support best-effort IP transport.

Support for additional features, include QoS, is defined in the
DOCSIS 1.1 spec.  This document is also available at the above
web site.


Some details about DOCSIS cable networks:

* On the HFC network, a single downstream channel can support
  ~25-35 Mb/s (depending on the modulation being used).

*  The upstream connection typically can support between 5-10 Mb/s
  (depending on modulation and the size of the channel).  

* The cable operator can opt, based on RF combining, how many homes
  (fiber nodes) share a downstream or upstream.    When service is
initially
  launched in an area, an operator might combine several nodes together
  and as the take rate increases, reduce the amount of combining
  (which effectovely reduces the number of customers who share the
   bandwidth).

* When a cable modem is brought online, it gets an IP address via
  DHCP and then is loaded with configuration information (IP, L2,
  and L4 filters), network management, etc information.   These
  filters prevent issues which arise when  DHCP servers are
  running in a customer's home, prevents my NETBIOS traffic from being
  seen by neighbors, etc.  

There are other technologies still deployed by cable operators to
support
HSD (LanCity, Motorola CDLP, Com21, etc.) which may not operate the same
as DOCSIS.  

Hope this helps.
	  


sam sneed wrote:
> 
> I just changed services from DSL to cable modem. I have heard from
people,
> including verizon, that cable is not as secure as DSL becuase it is
over a
> shared medium. I connected to my cable modem and fired up my packet
sniffer.
> I did not see anyone elses traffic on the line so i am assuming the
bandwith
> is shared( a known fact about cable access) but is somehow filtered at
the
> cable modem(bridge). Does anyone know if this assumption is true and
the
> inside details of the how data is transmitted over the cable network?
A
link
> to a whitepaer would be great.
> 
> thanks




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