Re: [Tsv-art] [Last-Call] [lp-wan] Tsvart last call review of draft-ietf-lpwan-coap-static-context-hc-12

Joseph Touch <touch@strayalpha.com> Tue, 17 March 2020 22:06 UTC

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From: Joseph Touch <touch@strayalpha.com>
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Date: Tue, 17 Mar 2020 15:06:06 -0700
Cc: dominique.barthel@orange.com, "tsv-art@ietf.org" <tsv-art@ietf.org>, The IESG <iesg@ietf.org>, "lp-wan@ietf.org" <lp-wan@ietf.org>, "last-call@ietf.org" <last-call@ietf.org>, "draft-ietf-lpwan-coap-static-context-hc.all@ietf.org" <draft-ietf-lpwan-coap-static-context-hc.all@ietf.org>, "draft-ietf-lpwan-ipv6-static-context-hc@ietf.org" <draft-ietf-lpwan-ipv6-static-context-hc@ietf.org>
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To: Benjamin Kaduk <kaduk@mit.edu>
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Subject: Re: [Tsv-art] [Last-Call] [lp-wan] Tsvart last call review of draft-ietf-lpwan-coap-static-context-hc-12
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My concern is Section 7.5.8.  How can both the IP and UDP lengths both be computed unless both depend directly on the link packet size?

AFAICT, With UDP options, the UDP length cannot be computed that way. The default rules need to take that into account.

I.e., you don’t need the UDP option TLVs if you don’t compress that area, but compression definitely needs to restore the UDP length as distinct from and unrelated to the IP length.

Joe

> On Mar 17, 2020, at 2:13 PM, Benjamin Kaduk <kaduk@mit.edu> wrote:
> 
>> In conclusion, the SCHC compression mechanism, if properly implemented, is
>> fully compatible with draft-tsvwg-udp-options.
> 
> This "if properly implemented" seems pretty critical.  Do we need to leave
> a reminder that implementations have to know about UDP TLVs in order to
> properly identify all fields in the headers to be compressed?
> 
> -Ben