Re: [rohc] question about draft-bormann-rohc-over-802-00.txt

Carsten, did you find any AP that allow the reception of LLC frames,
but always send DIX frames when bridging to a different 802 link type?
(e.g. receive a 802.11 frame with LLC and forward a 802.3 DIX frame)

In my previous messages, I made the assumption (maybe an incorrect
one) that most bridges would behave like this. But maybe there aren't
any APs with this kind of behaviour. I didn't made any tests yet.

Best Regards,
Pedro Fortuna
=======================
Faculty of Engineering (FEUP)
University of Porto
Portugal

On Tue, 29 Mar 2005 14:51:29 +0200, Carsten Bormann <cabo@tzi.org> wrote:
> On Mar 25 2005, at 23:22 Uhr, Pedro Fortuna wrote:
> 
> > In my opinion it will be difficult for a 802.2 based solution to work
> > with legacy equipment, because bridges/APs are programmed to send DIX
> > frames by default (they support receiving 802.2 frames, but normally
> > do no send them when bridging from other 802 technologies).
> 
> We did some quick experiments before I wrote the draft.
> We found three classes of APs:
> 
> 1) APs that just discard length-field (LLC)) frames.  If we use LLC for
> the negotiation protocol, too, then when these are in the path,
> ROHC-over-802 implementations would never negotiate ROHC in the first
> place.  Not a problem.
> 2) APs that mangle LLC frames.  For instance, one AP received an LLC
> frame and "corrected" the length field to include the Ethernet padding
> before sending it forward.  Again, the negotiation protocol could
> include some sanity checks here.
> 3) Correct APs.
> 
> The first two classes are generally known in the community as "don't
> support Appletalk".
> They do exist, but have become rarer.
> 
> In my opinion a solution that only supports class 3, but is robust in
> the presence of classes 1 and 2, would be fine.
> 
> Gruesse, Carsten
> 
>

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