Subject: [lp-wan] Tickt #5: Decoupled Fragmentation and SCHC compression

From: Ana Minaburo <[email-masked]>
Date: Mon, 26 Feb 2018 22:24:53 +0100

Maybe it is possible to mention that the fragmentation can be decoupled and
located near the NGW since for some LPWAN technologies there may be timing
constraints?

The Fragmentation and Compression are not decoupled because different
locations imply different SCHC instances in the architecture, do we want to
define this?
And Architecture Modification is an implementation issue

Ana: I think we can have different instances of SCHC where some of them
only done compression and some other only fragmentation, but this is not
defined in the actual version of the draft, normally you make compression
and if you need you use fragmentation or not depending on the L2 PDU size.
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Interim 16th

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   - fragmentation and compression are described together in the
   architecture. Suggestion to have them decoupled. Fragmentation may be done
   at application server, etc. Pascal: Laurent: separate compression for CoAP
   and for UDP/IPv6. Can be bunched together later. Recommend to keep
   fragmentation and compression together. Edgar: Some technologies has
   multiple reception points, which means that the reconstruction of the
   packet (if fragmented) has to be done in a point after the combining of
   packets is done. This restricts the places where the fragmentation is
   placed. In practice, this might be very close or just same place where the
   decompresion happens. Ana: we can have a SCHC function in various places of
   the architecture. Each instance can do either one or both of fragmentation
   and compression. Alex: add a sentence in the doc? Pascal: curious that the
   doc need a lot of changing if SCHC is divided in compression and
   fragmentation Ana: It is in the document, but for now you always have SCHC
   and fragmentation together in the same place. Maybe in the future we can
   have them split into multiple places. Edgar: on first reading, had
   difficulty understanding the flow. What is supposed to happen, in what
   order? the doc goes back and forth between compression and fragmentation.
   Edgar: especially the compression section seems less clear on the flow, the
   mechanism. The connection between the two (frag and compr) is not clearly
   described either. Pascal: inherited from the 6LoWPAN mindset Ana shows a
   diagram with compressed packet followed by the fragmentation. Dominique: we
   need to come up with a name for the "SCHC packet". The text currently uses
   various circonlocutions for it.
   - Pascal: some sentences could be written in clearer English. Beleives
   that the intended meaning is what we want, but the way it is expressed
   might be misleading.

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Ana: With the terminology sublayers, is this point more clear? Do we need
to add something else?