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" <[email protected]>
Date: 8/18/2016 18:11 (GMT+01:00)
To: [email protected]
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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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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