Mailing List SIMS@mail.stalker.com Message #14869
From: Bill Cole <listbill@scconsult.com>
Subject: Re: Wandering off-topic: Speedstream 5861 (was Re: Authentication Attempts)
Date: Wed, 1 Dec 2004 23:15:30 -0500
To: SIMS Discussions <SIMS@mail.stalker.com>
At 10:53 PM -0500 12/1/04, Alex von Thorn  imposed structure on a stream of electrons, yielding:
No, Ethernet is a layer-two protocol, DSL is a layer-one protocol. A DSL modem modulates and demodulates a DSL signal (hence the name "modem") to another data link protocol (commonly but not necessarily Ethernet). Physical protocols are about signalling and electrical signals which form bits on a physical medium; data link protocols group bits together into bytes and frames, over any physical medium. DSL commonly uses Ethernet because home computers have Ethernet ports and DSL modems often act simply as an Ethernet bridge with no network routing function. Theoretically, one could use DSL to carry PPP (though that would be very odd), ATM, frame relay, MPLS, or whatever.

FWIW, SBC (one of the largest DSL providers) in most areas layers ATM over DSL and PPP over the ATM virtual circuit to get the IP layer up. That is a reasonably common approach, as it has some provider-side advantages over making the intrinsically point-to-point DSL look like an Ethernet and then running DHCP over it.

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Bill Cole                                  bill@scconsult.com

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