Re: Meta-issues: On the deprecation of the fragmentation function

[RJ Atkinson <[e-mail]>]

> On Jul 9, 2013, at 17:02, RJ Atkinson <[e-mail]> wrote:
>> The IPv6 concept of adding a special link-specific
>> fragmentation/reassembly protocol layer has never been
>> practical.  

My comment (above) was in the context of the kinds of
low-bandwidth links with smaller MTU sizes that I was
discussing, of course. :-)

On 09  Jul 2013, at 12:38 , Carsten Bormann wrote:
> For 6LoWPAN, we did (we had to).  And it works well enough.

I am happy to accept your word that it works well enough
for 6LoWPAN (i.e. IEEE 802.15.4).  Of course, it helps
that IEEE 802.15.4 links support up to 250 Kbps, which is 
visibly higher capacity than a number of RF links that
are deployed with IPv4 today.

However, I also have experience indicating that link-specific
fragmentation/reassembly does NOT work as well as simply
inserting an IPv6 Fragmentation Header -- at least for 
some other low-speed, smaller MTU, RF link layers that
work adequately with IPv4 today.  

Various obvious things, such as header compression, 
already are commonly used on such low-bandwidth RF links.

> But for one problem: adaptation layer fragmentation is
> *transparent*, so there is no way for an application
> to do the equivalent of PMTUD to avoid/minimize adaptation
> layer fragmentation.

Good point.

Yours,

Ran