Re: Review of draft-bberry-pppoe-credit (Informational)

On 27 Jul, Vernon Schryver wrote:
> What?  That's not the draft I thought it was.  How stupid can I get?
> 
> Having now bothered to read it, I can't help wondering what PPPoE has
> to do with the problem or the solution.  Why can't you do the same
> things without having wasting precious radio bandwidth on 802.3 headers
> and trailers?

It's not PPPoE end-to-end between the PPP endpoints.
Unlike regular PPPoE, the termination point of the PPPoE and PPP don't 
coincide anymore.  The radio is merely creating an illusion of this to its 
attached router.  PPPoE is running between the router and its
host radio, not between the router and a peer router.  The flow
control, for example, is not one PPP endpoint giving credits to the
other endpoint, it is merely the radio telling its attached router that
it has available buffer space to take more packets. 

PPPoE is really just being used as a means to multiplex multiple
PPP sessions over the ethernet link to the radio, and as a carrier
for signalling info between radio and router.

The packets over the airwaves aren't PPPoE in nature, and for that matter 
how the remote PPP device talks to its host radio might be entirely 
different than the local end (the remote device might have a built-in
radio and simply see "RLP" as its native encapsulation for example,
and handle flow control far more efficiently than the other end with
its ethernet-connected radio).

A completely new protocol could have been devised for all of this,
but since the nature of the info traded by that protocol would have
been very much like the nature of the info traded by PPPoE, I think
the authors wanted to use PPPoE precisely so they wouldn't be
completely reinventing the same old wheel.  The purpose of the document
isn't to make a general-purpose extension to PPPoE, it's to create
a special purpose extension for a very specific sort of environment.

Lest I sound too authoritative, I should qualify that this is my
understanding based on past discussions I've had with the group
which is behind this draft.

-Mark Lanzo


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