Subject: Re: I-D ACTION:draft-nanji-l2tp-eth-00.txt

From: Suhail Nanji <[email-masked]>
Date: Thu, 6 Jul 2000 16:56:37 -0700 (PDT)

James Carlson writes:
> > 	Title		: Ethernet Encapsulation Extensions to Layer Two 
> >                           Tunneling Protocol
> 
> Two questions: doesn't BCP over PPP already provide a well-defined,
> standards-track superset of this functionality?  Shouldn't this draft
> at least reference BCP and indicate why the currently used mechanisms
> for bridging over point-to-point links are insufficient?

You make a good point, the draft should at least reference BCP and mention
why it is insufficient.  The next revision of the draft will include this
change.

BCP over PPP over L2TP is reasonable, but this adds protocol overhead, and
requires that someone run PPP.  In many broadband environments, the end
user is communicating from their PC out their Ethernet interface to a
bridging modem.  The end user is not necessarily running PPP.  The modem is
designed to be inexpensive and is also not running PPP.  This is a very
common model for both DSL and Cable.  That Ethernet link then extends to an
access concentrator that may not terminate the connection, but wishes to
tunnel it to another access concentrator.  Since the connection from the
end user is Ethernet, we are proposing a method to extend that
Ethernet link over L2TP. Since Ethernet is a Layer 2 protocol, it seems
reasonable to extend the Layer 2 Tunneling protocol (L2TP) to tunnel it.
In DSL, the individual Ethernet links from each modem are still chanelized
so L2TP seems an ideal way to maintain that chanelization to the LNS.

> 
> -- 
> James Carlson, Internet Engineering       <[email-masked]>
> SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
> MS UBUR02-212 / Burlington MA 01803-2757   42.497N   Fax +1 781 442 1677
> "PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp

---

From: Theimer Thomas <[email-masked]>
Date: Mon, 10 Jul 2000 15:08:08 +0200

Suhail Nanji writes: 
> Theimer Thomas writes:
> > 
> > 	Suhail Nanji writes:
> > > The end user is not necessarily running PPP.  The modem is
> > > common model for both DSL and Cable.  
> > > 
> > 	[Theimer Thomas]  
> > 	Two questions for clarification:
> > 
> > 	1. What is the link layer between modem and access concentrator ? If the answer is ATM or FR, then why is bridging over ATM/FR not sufficient ?
> > 
> 
> Bridging is sufficient to get it to the first access concentrator but from
> there some protocol is needed to have the Ethernet frame tunneled to
> another access concentrator which would be the point of termination.
> 
	[Theimer Thomas]  What is wrong with encapsulating the Ethernet frame in PPP over L2TP ? It only costs a couple of extra header bytes, but does not need any new protocol or encapsulation. You can simply extend the Ethernet-over-ATM bridge into another Ethernet-over-PPP-over-L2TP bridge. Note that PPP here is not per user, it is simply a tunnel encapsulation.

	Thomas