Subject: PPP over Ethernet Phy

From: John Sauer <[email-masked]>
Date: Tue, 05 Mar 2002 11:10:54 -0600

Group,

Earl McCoy and I have written an I-D on PPP over a slimmed down
Ethernet.  The thrust is to remove some functional duplication between
IP and underlying Ethernet.  We think it is applicable to the pppext
group and would like to get your opinion on the draft. See the I-D info
below.

Thanks,

John 

PS - I already know I got the wrong year on the expiration date on some
pages. :-)

####

A New Internet-Draft is available from the on-line Internet-Drafts
directories.

        Title           : PPP over Full Duplex Point-to-Point Ethernet
Physical
                          Layers
        Author(s)       : E. McCoy, J. Sauer
        Filename        : draft-mccoy-pppext-pppoephy-00.txt
        Pages           : 12
        Date            : 21-Feb-02

This document provides a definition for encapsulating the PPP
protocol directly on the various full duplex point-to-point Ethernet
physical layers. The later includes transmission bit rates of
10Mbps, 100Mbps, 1Gbps, and 10Gbps. Note this is a distinct protocol
from PPPoE, as the Ethernet frame is not existent here.  All PPP
packet semantics and syntax are retained. The proposed methods in
this document may be especially useful for low cost, high bandwidth
physical channel implementations. In particular it specifies and
redefines all necessary Ethernet Medium Independent Interface
functional 'clauses.'

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-mccoy-pppext-pppoephy-00.txt

--
----------------------------------------------
John Sauer             [email-masked]
Tellabs Operations     ph: 630.798.5581
1415 West Diehl Road   fx: 630.798.5744
Naperville, IL 60563
----------------------------------------------
============================================================
The information contained in this message may be privileged 
and confidential and protected from disclosure.  If the 
reader of this message is not the intended recipient, or an 
employee or agent responsible for delivering this message to 
the intended recipient, you are hereby notified that any 
reproduction, dissemination or distribution of this 
communication is strictly prohibited. If you have received 
this communication in error, please notify us immediately by 
replying to the message and deleting it from your computer.

Thank you.
Tellabs
============================================================

---

From: Dennis Ferguson <[email-masked]>
Date: Sat, 09 Mar 2002 19:13:48 -0800

John,

> group and would like to get your opinion on the draft. See the I-D info

I read this with some interest, but discovered I didn't understand
the punch line.  For the benefit of the uneducated could you perhaps
at least include a hint in the document about what a PPP frame is supposed
to look like when encapsulated directly on an Ethernet Physical Layer
without the Ethernet MAC Layer?  For example, is the protocol packet
preceded solely by the two-byte PPP protocol identifier, or are there
other bytes at the front of the packet too?  Does the frame include an
FCS, and if so is it a 16-bit or a 32-bit CRC, or what?  Are the bits
in bytes put on the wire with the most significant or least significant
bit first?  Do frames still need to be padded out to a minimum of 64
bytes?  It is kind of hard to guess this stuff, but it would be easy to
draw a few pictures.

If you are into describing things in terms of layers, then I think
part of the confusion here is that PPP itself is only about half of
a "layer 2" and always borrows the other half (framing procedures, error
detection and stuff like that) from something that works appropriately
over the physical layer in question.  For example, "PPP over SONET/SDH"
isn't really "PPP over SONET/SDH", it is "PPP in Octet-Synchronous HDLC
U/I Frames over SONET/SDH", with the document incorporating what HDLC
octet-synchronous HDLC U/I frames look like to make it easy for
implementors.  Similarly, PPPoE is really "PPP in Ethernet MAC layer
frames over Ethernet Physical Layers", and you can't just chuck out
the MAC layer framing without fully specifying the framing procedures
you are replacing it with, because there are no generic PPP framing
procedures to replace it with.  You have to make them up.

The question I'm really fascinated with, however, is why you want to
do this at all?  I understand from this

   This places the data service industry in a dilemma, namely wishing
   the less costly physical interface of Ethernet layer 1, but not
   actually needing or wanting Ethernet`s redundant layer 2 packet
   switching capability, scaling problems, etc.
[...]
   Alternatively, and proposed here, is to retain Ethernet`s full
   duplex point-to-point physical interface alternatives, but define
   PPP encapsulation directly - leaving out the redundant MAC frame and
   hence all Ethernet Layer 2 functionality.  The authors believe this
   is the best of both worlds, and consistent with the Internet`s
   proven architectural principles.

that what you want to accomplish is to remove Ethernet switches from the
links between routers, or routers and hosts, but I can't for the life of
me figure out why the goal of removing Ethernet switches is not fully
accomplished by simply removing the Ethernet switches, wiring the routers
and hosts directly together instead?  Once the Ethernet switches are
physically removed you no longer have a redundant layer 2 packet switching
capability, so replacing the Ethernet MAC-level framing in addition to
that is unnecessary for this purpose.  What additional advantage are
you trying to get by doing the latter?

Enquiring minds want to know.

Dennis Ferguson