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

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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