Re: [tcpm] Long tail of TCP stacks (was: RE: draft-ietf-tcpm-accurate-ecn-24 addressingallWGLCcomments)

Hi,

Just an additional detail beyond what has already been explained: at the
time of writing RFC 9006, none of the 7 considered TCP implementations for
constrained devices supported ECN, while 2 of the implementations supported
SACK.

A summary of these (and other) features is available in Appendix A (section
A.7) of RFC 9006.

Cheers,

Carles

On Wed, 27 Sept 2023 at 11:06, Scharf, Michael <
Michael.Scharf@hs-esslingen.de> wrote:

> Hi Richard,
>
> Yes, I had a look at ECN and SACK. As far as I can tell, a lot of "basic"
> IoT stacks neither support SACK nor ECN (RFC 3168), albeit it is a bit
> difficult to know for sure for some closed-source stacks. I have only found
> ECN support in the well-known "high-end" stacks that are used also for
> desktop and server computers.
>
> SACK seems more prevalent than ECN, since some "basic" stacks such as lwIP
> support SACK (well, at least partly).
>
> However, one interesting insight in my survey was that one open source
> stack has different license conditions for its SACK and its ECN code.
>
> This could imply that some commercial IoT implementations could use the
> open source ECN implementation, but they may not be able to use SACK due to
> formal license problems.  In this specific context, it could indeed be
> possible that ECN (or even AccECN, if available) is supported, but not
> SACK. The root cause would be the difference in license conditions.
>
> Of course, a theoretical work-around in this case would be an entire SACK
> implementation from scratch, but this may not be a low-hanging fruit.
>
> As far as I understand, such a use of "ECN without SACK" would have a
> non-technical root cause. But this could be a real-world issue in running
> code...
>
> Michael
>
>
> > -----Original Message-----
> > From: rs.ietf@gmx.at <rs.ietf@gmx.at>
> > Sent: Wednesday, September 27, 2023 10:18 AM
> > To: tcpm@ietf.org; Scharf, Michael <Michael.Scharf@hs-esslingen.de>
> > Subject: Re: [tcpm] Long tail of TCP stacks (was: RE:
> draft-ietf-tcpm-accurate-
> > ecn-24 addressingallWGLCcomments)
> >
> >
> > Out of curiosity, did you investigate how many of these IoT stacks
> support
> > ECN (negotiation, ECT-marking of sent messages, and RFC3168 ECE/CWR
> > feedback)?
> >
> > WOuld be interesting to see, if SACK or ECN is more prevalent in these
> > implementations...
> >
> > Richard
> >
> >
> >
> > Am 23.09.2023 um 12:01 schrieb Scharf, Michael:
> > > In don't plan to get involved into this WGLC discussion and this
> e-mail is not
> > about AccurateECN.
> > >
> > > Yet, I have a general comment related to the long tail of TCP stacks...
> > >
> > >>> How many stacks are out there not supporting TCP SACK? How many of
> > >> them will implement
> > >>> ECN++?
> > >>
> > >> [MK5] I think tens if not hundreds, when all various devices like
> network
> > >> printers and stacks in various IoT appliances, vehicles, etc are
> counted.
> > >
> > > [...]
> > >
> > > I think this number from Markku is realistic. See also RFC 9006.
> > >
> > > I have recently surveyed some IoT stacks. Well, there is really a
> large number
> > of different TCP/IP stacks out there. Some only support the most basic
> > standard track TCP features (if at all).
> > >
> > > In TCPM (and the IETF as a whole), IMHO we often focus on desktop and
> > server operation systems. Yet, in IoT and some other network domains that
> > increasingly get connected to the Internet, TCP/IP implementations can be
> > different to what is the default in Linux, Windows, BSD, etc. I believe
> that, as of
> > today, one cannot assume that all TCP stacks relevant for the Internet
> indeed
> > support and enable SACK. Of course, the same applies to ECN.
> > >
> > > For what it is worth, one example mentioned in RFC 9006 is lwIP
> > (Leightweight TCP/IP). Recent versions of lwIP support at least sending
> SACK
> > options, but the logic is very simple (as far as I understand). As far
> as I can tell,
> > lwIP is fairly sophisticated as compared to other IoT stacks that are
> much more
> > rudimentary.
> > >
> > > Recently I tried to come up with a simple lwIP example for my
> students. I
> > ended up creating an echo server example that runs in Linux user space:
> > https://github.com/michael-scharf/lwip-echoserver
> > >
> > > If someone else is interested in playing with lwIP, maybe such an
> example
> > can help...
> > >
> > > Michael
> > >
> > > _______________________________________________
> > > tcpm mailing list
> > > tcpm@ietf.org
> > > https://www.ietf.org/mailman/listinfo/tcpm
> _______________________________________________
> tcpm mailing list
> tcpm@ietf.org
> https://www.ietf.org/mailman/listinfo/tcpm
>