[riot-devel] Fragmentation support in IP

Martine Lenders authmillenon at gmail.com
Fri Aug 19 09:56:33 CEST 2016


Hi Adeel,
What do you mean by "lost fragment recovery"? To my knowledge there is no
such thing in 6LoWPAN fragmentation.

Regards,
Martine

Am 19.08.2016 12:59 vorm. schrieb "Adeel Mohammad Malik" <
adeel.mohammad.malik at ericsson.com>:

> Hi again Thomas,
>
> Do you mean that 6LoWPAN in RIOT does not support lost fragment recovery?
> Assuming it does, what I had in mind was that we could segment data in the
> application to the IP MTU and leverage the lost fragment recovery feature
> in 6LoWPAN to get a decent performance. This way we may not need to
> implement lost segment recovery in the application. But if 6LoWPAN in RIOT
> does not support recovery of lost fragments we might as well run our
> application direclty on link layer (since we dont need IP routing).
>
> /Adeel
> -------- Original message --------
> From: "Thomas C. Schmidt" <t.schmidt at haw-hamburg.de>
> Date: 8/18/2016 23:27 (GMT+01:00)
> To: RIOT OS kernel developers <devel at riot-os.org>
> Cc: Börje Ohlman <borje.ohlman at ericsson.com>, Joakim Borgh <
> joakim.borgh at ericsson.com>
> Subject: Re: [riot-devel] Fragmentation support in IP
>
> Hi Adeel,
>
> adding to this: you should keep in mind that in LowPANs you may easily
> trigger multiple layers of fragmentation (loosing one fragment is
> loosing all!) ... and that receivers may not be ready to handle UDP
> datagrams of 'arbitrary' sizes.
>
> So if you really want to stay away from upper layer protocols like CoAP,
> you should process data segmentation in your application (not sure this
> is the best idea, though).
>
> Cheers,
>   Thomas
>
> On 18.08.2016 22:54, Carsten Bormann wrote:
> > Hi Adeel,
> >
> > IP fragmentation is usually a bad idea*), and more so on a constrained
> > network.  If you need to transfer payloads beyond a kilobyte or so,
> > maybe CoAP (RFC 7252) with the block-wise transfer protocol (currently
> > being published as RFC-to-be 7959) solves your problem.
> >
> > Which encryption expands a few bytes of plaintext to kilobytes of
> > ciphertext?  (You may be thinking about signatures; e.g., hash-based
> > signatures can be 3-6 KiB or even more.  These might occur in firmware
> > updates and are covered quite well by CoAP + block-wise.)
> >
> > Grüße, Carsten
> >
> > *)
> > https://tools.ietf.org/html/draft-mathis-frag-harmful-00
> > http://www.hpl.hp.com/techreports/Compaq-DEC/WRL-87-3.pdf
> >
> > Adeel Mohammad Malik wrote:
> >> Hi Thomas,
> >>
> >> I agree that IP fragmentation is not an equivalent for data streaming.
> >> However it still facilitates transporting data that exceeds the MTU. The
> >> use case we are looking at is encryption of IoT data that may result in
> >> a few bytes of plaintext being converted to a few kilobytes of
> >> ciphertext. Had IP supported fragmentation in RIOT it would have been
> >> possible for us to send such data.
> >>
> >> /Adeel
> >>
> >>
> >> -------- Original message --------
> >> From: "Thomas C. Schmidt" <t.schmidt at haw-hamburg.de>
> >> Date: 8/18/2016 18:11 (GMT+01:00)
> >> To: devel at riot-os.org
> >> Subject: Re: [riot-devel] Fragmentation support in IP
> >>
> >> Hi Adeel,
> >>
> >> GNRC in RIOT supports fragmentation, e.g. in the context of 6LowPAN.
> >>
> >> However, you seem to be interested in sending UDP datagrams that exceed
> >> the MTU payload size. I don't think this is common use ... and I don't
> >> think this is clever, either. IP fragmentation is not an equivalent for
> >> data streaming.
> >>
> >> Cheers,
> >>   Thomas
> >>
> >> On 18.08.2016 18:04, Adeel Mohammad Malik wrote:
> >>> Hi all,
> >>>
> >>>
> >>>
> >>> My question is about fragmentation support in IP in RIOT. Does IP in
> >>> RIOT support fragmentation? The use case I am after is transferring a
> >>> large blob of data (let’s say 5 kilobytes) on the UDP/IP stack in RIOT.
> >>> Is that possible?
> >>>
> >>>
> >>>
> >>> I know that 6LoWPAN supports fragmentation but that is below the IP
> >>> layer. I am interested in fragmentation at the IP layer so that
> >>> application running over it in RIOT can send large data.
> >>>
> >>>
> >>>
> >>> Regards,
> >>>
> >>> Adeel
> >>>
> >>
> >> --
> >>
> >> Prof. Dr. Thomas C. Schmidt
> >> ° Hamburg University of Applied Sciences                   Berliner Tor
> 7 °
> >> ° Dept. Informatik, Internet Technologies Group    20099 Hamburg,
> Germany °
> >> ° http://www.haw-hamburg.de/inet                   Fon:
> +49-40-42875-8452 °
> >> ° http://www.informatik.haw-hamburg.de/~schmidt    Fax:
> +49-40-42875-8409 °
> >> _______________________________________________
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> >>
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>
> --
>
> Prof. Dr. Thomas C. Schmidt
> ° Hamburg University of Applied Sciences                   Berliner Tor 7 °
> ° Dept. Informatik, Internet Technologies Group    20099 Hamburg, Germany °
> ° http://www.haw-hamburg.de/inet                   Fon: +49-40-42875-8452
> °
> ° http://www.informatik.haw-hamburg.de/~schmidt    Fax: +49-40-42875-8409
> °
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