Re: Corrections/Evolutions for ULE draft

[alain.ritoux@6wind.com]

Gorry Fairhurst wrote:

> There is one thing I'd like to get a feeling for from the list:
>
>    Do we need to support a maximum paylaod size of approx 64KB?
> I've asked this several times, and most people seem to agree we don't 
> need to support payloads this big, nor is it likely to be significant 
> issue for this type of network in the future. I'd advocate at least 16 
> KB, could we live with a little less than 32 KB as the maximum payload 
> size??? Is there anyone with other views out there?
> Thoughts?

Indeed, I once proposed to reduce it more than that, but mainly I
was thinking "ethernet", and I see now that in the core, MTU are
getting higher !!
On FreeBSD implementation ATM interface have ~9K MTU. And I've read
something about some links also with 9K MTU. I feel comfortable
with 16K, which leaves 2 bits for any creative usage ;-)

btw : what about next header in ULE method, for as alignement is
clearly not aimed, maybe 1 byte is enough, reducing encaps overhead
from 8 to 7. And to kkep possible type extension (if 256 space
gets exausted, the mlength field, could be specified to cover
type-field + payload + CRC, instead of just  payload + CRC

still "next header" considerations:  if is is an ether_type, there
can be pb for non-defined ether_types, such as ROHC :-(
and so it would block the draft UNTIL and ether type is (ever?)
adopted, because choosing a non-ether-type for one of the protocols
might result in a future conflict.
same thing for PPP-types : I haven't found PPP-type for MPLS

still with the same subject : are two differnet values needed for
ROHC4 and ROHC6, for ROHC packets are asociated to specific flows
that share some common info (such as addresses, and especially IP
version!). I had a look a RFC3241, and there is no ROHC-v4 and
ROHC-v6 separation for PPP, rather a separation between
ROHC-with-small-CID ROHC-with-large-CID, which is said not to be
needed ("p2 ROHC does not require that the link layer be able to
indicate the types of datagrams carried in the link layer
frames.") ????
So, I think, a single netx header value could be used.

Your thoughts ?

Cheers.
Alain.
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Alain RITOUX
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