Adaptation Layer Fragmentation Indication

Carsten Bormann <> Wed, 25 April 2012 16:17 UTC

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Subject: Adaptation Layer Fragmentation Indication
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From: Carsten Bormann <>
Date: Wed, 25 Apr 2012 18:17:00 +0200
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I have written a small Internet-Draft that addresses a long-standing problem in the 6lowpan space.  As usual, it is on the boundary between 6man and intarea, but I think the general considerations behind this fit intarea a bit better.

I don't see a need to push this specification forward at great speed, but there have been discussions in other spaces that appear to make it useful to have this facility.  If you are interested in constrained networks, please have a look, and comment to the list.

Grüße, Carsten

Begin forwarded message:

> From:
> Subject: I-D Action: draft-bormann-intarea-alfi-00.txt
> Date: April 25, 2012 17:50:02 +0200
> To:
> Reply-To:
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> 	Title           : Adaptation Layer Fragmentation Indication
> 	Author(s)       : Carsten Bormann
> 	Filename        : draft-bormann-intarea-alfi-00.txt
> 	Pages           : 13
> 	Date            : 2012-04-25
>   IPv6 defines a minimum MTU of 1280 bytes.  Many link layers are more
>   limited in their choice of packet size.  Typically, IP adaptation
>   layers for these link layers define a segmentation or fragmentation
>   scheme to transport larger IP packets in multiple link layer packets.
>   Often, adaption layer fragmentation schemes reduce some performance
>   metric, such as the packet delivery rate.  Where application or
>   transport protocols have a choice, it would therefore be desirable
>   for them to know about any adaptation layer fragmentation that is
>   going on, so they can choose packet sizes that minimize adaptation
>   layer fragmentation.
>   At the IP layer, fragmentation can be detected using a number of
>   mechanisms used in Packetization Layer Path MTU Discovery [RFC4821].
>   However, adaptation later fragmentation schemes are often designed to
>   be "transparent", i.e. there is no way at higher layers to find out
>   they had to be employed (except maybe by elaborate measurement
>   schemes targeting one of the impacted performance metrics; this
>   approach does not appear to be viable) [WEI].
>   The present specification defines a mechanism for IPv6 adaptation
>   layers to indicate the presence of adaptation layer fragmentation, as
>   well as an indication of preferred packet sizes.
>   The main objective of this version of the draft is to present a
>   complete design in order to be able to gauge the complexity of the
>   approach against the gains to be expected from implementing it.
>   Comments are appreciated and should go to the
>   mailing list.