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Jeff Liebermann  
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 More options Oct 5 2012, 12:12 pm
Newsgroups: sci.electronics.repair
From: Jeff Liebermann <je...@cruzio.com>
Date: Fri, 05 Oct 2012 09:12:14 -0700
Local: Fri, Oct 5 2012 12:12 pm
Subject: Re: Internet connection
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On Thu, 04 Oct 2012 21:25:59 -0700, josephkk

<joseph_barr...@sbcglobal.net> wrote:
>On Thu, 04 Oct 2012 09:20:07 -0700, Jeff Liebermann <je...@cruzio.com>
>wrote:

>>Not bigger network, but different network.  The definition of a router
>>is a device that connects two DIFFERENT networks at the IP layer (ISO
>>layer 3).  One port is connected to the greater internet network.  The
>>other port is connected to a local area network, that uses
>>non-routeable IP addresses.

>I mostly agree with your distinction on the difference between modem and
>router.

It's an oversimplified definition, which falls apart on devices like a
brouters (bridge-router) and using a DSL modem to simultaneously
connect to multiple services.  Simple definitions never seem to stay
simple.

>>My definitions, which might be different than yours:

>>DSL Modem:  DSL (actually ATM) to ethernet bridge.  Everything done at
>>the MAC layer (ISO Layer 2) with no involvement with IP layer (ISO
>>layer 3) except for configuration management.

>I do not think that what is appearing at the DSL end user terminals is ATM
>but closer to VT45 or VT135 with highly compressed data.  Moreover you are
>looking at data likely being a shared service with a much more broadband
>(TV) type service on the same pair.

>?-)

Ok, you got me.  What is V45 and V135?  Google wasn't particularly
helpful by suggesting that VT meant vacuum tube.  Are you thinking of
AT&T U-Verse IPTV service which uses VDSL?  If so, I know nothing
because AT&T doesn't offer it in my area.

The DSL modem with diagnostics include "ATM Ping" which should be a
clue.  Articles on how DSL works always mention ATM as the underlying
virtual circuit mechanism to connect to the DSLAM (ATM switch) which
does the IP packet reassembly from the tiny ATM pieces.
<http://www.eetimes.com/electronics-news/4140135/ADSL-Technology-Expla...>
See section "ADSL and ATM".

--
Jeff Liebermann     je...@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558


 
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