Re: [iccrg] [CCWG] [tsvwg] New Internet Draft: Congestion Signaling (CSIG)

[Hesham ElBakoury <[e-mail]>]

Speaking of Internet congestion control, have you looked at this paper:
Future Internet Congestion Control: The Diminishing Feedback Problem [
https://arxiv.org/pdf/2206.06642]? The abstract of this paper says: *<we
argue that congestion control mechanisms should move away from their strict
“end-to-end”*
*adherence. This change would benefit from avoiding a “one size fits all
circumstances” approach, and moving towards a more*
*selective set of mechanisms that will result in a better performing
Internet.*>

Hesham

On Thu, Sep 14, 2023, 3:23 AM Sebastian Moeller <[e-mail]> wrote:

> Hi Ruediger,
>
>
> > On Sep 14, 2023, at 09:25, <[e-mail]> <
> [e-mail]> wrote:
> >
> > Sebastian, Ingemar,
> >
> > the draft says "limited domain". The method suggested resembles IPPM's
> IOAM (but the packet size remains fixed, certainly an advantage).
> Information like a port ID only makes sense, if the evaluation unit is
> aware of the domain-topology.
>
>         [SM] Not sure I understand this, if on an internet-wide path all
> nodes would simply include the minimum of their egress bitrate (that is
> only include this if it is lower than the existing value), then an end-2end
> protocol like TCP could even as part of the initial 3 way handshake figure
> out a hard limit for maximum rasinsable cwin (by simply calculating the
> BDP). SUre that would not stop slow-start fuully from overshooting, but it
> should limit the maximum overshoot considerably....
>
>
> > That will be restricted to a single domain, I think.
>
>         [SM] As long as the forward and collection path requires L2
> elements, sure this will not work over the internet.
>
>
> > I'm also not sure, what is to be optimized on an operational carrier
> backbone.
>
>         [SM] I trust you on this, as that is out of my league.
>
>
> > Under expectable conditions, these are operated without congestion.
> Bottlenecks are likely at the access and, in a rather limited number of
> cases, at peering. There you'd need to know the RTT so that the available
> bandwidth calculation makes sense.
>
>         [SM] But the protocol that is supposed to consume the congestion
> information will know the RTT, so can take this into account, the network
> really only needs to give information about its current state. That said, I
> can see network nodes that might want to know a flow's RTT, but I do not
> think there is a way of supplying that this is not both easy and efficient
> and not easily gamed. Passing on congestion informatin however is far less
> abusable (after all the node could just as well have dropped the packet
> instead of bothering to fudge the congestion info).
>
>
> > Or you need to calculate several values for several RTTs and provide
> this information (RTTs and corresponding available bandwidths). Requires a
> fair amount of bytes, so then trust may be an issue (I'm not sure whether a
> carrier would be willing to add an extended Ethernet header to every
> encrypted IP packet indicating interest in getting CSIG information on
> bottleneck links).
>
>         [SM] Yes encryption/privacy are reasons to stick to L2/L3. I would
> guess in a limited domain deploying CSIG as a pseudo VLAN header seems like
> a nice work-around, but this information really should be inside IP header
> to go end to end. IMHO it also should not be in an optional header, but
> should have been part of the mandatory header, but that ship has sailed
> long ago... It turns out that the mechanism intended here IPv6 extension
> headers was mis-deployed... (It should have been initiated with a really
> desirable use-case so it would actrually see usage immediately, protocol
> design is a bit like evolution, in both cases "use it or loose it" applies
> to some degree.)
>
> Regards
>         Sebastian
>
>
> >
> > Regards, Ruediger
> >
> > -----Ursprüngliche Nachricht-----
> > Von: Sebastian Moeller <[e-mail]>
> > Gesendet: Donnerstag, 14. September 2023 08:49
> > An: Ingemar Johansson S <[e-mail]>
> > Cc: Geib, Rüdiger <[e-mail]>; [e-mail];
> [e-mail]; [e-mail]; [e-mail]
> > Betreff: Re: [tsvwg] [iccrg] New Internet Draft: Congestion Signaling
> (CSIG)
> >
> > Hi Ingemar
> >
> >> On Sep 14, 2023, at 08:42, Ingemar Johansson S <
> [e-mail]> wrote:
> >>
> >> Hi Ruediger
> >>
> >> Even though CSIG is on ethernet, it appears to be e2e as the feedback
> is on L4. So I guess somehow the CSIG info needs to jump from domain to
> domain somewhow, and that sounds to me like L3, albeit perhaps brief jumps
> ?
> >
> >       [SM] rfc3168 and L4S ECN signaling faces the same hurdle, forward
> path uses a different layer than feed-back path. And I do not think that it
> is conceptually all that cleaner to have fewer layers between forward and
> reverse signaling... "clean" would be to put both forward and reverse
> information into the same layer, but that is not on the table as far as I
> can see.
> >       The other difference however, richness of signal, is a clear
> difference between 1 bit ECN and multibit CSIG (and alternatives).
> (Side-note, sure the ECN bitfield is two bits but it only carries 2
> congestion states when ECN is in use, which makes it IMHO a 1-bit
> information channel, if we had followed the SCE proposal with its 3
> congestion states we would be at 1.5 bits ;))
> >
> > Regards
> >       Sebastian
> >
> >
> >
> >>
> >> /Ingemar
> >>
> >>> -----Original Message-----
> >>> From: [e-mail] <[e-mail]>
> >>> Sent: Wednesday, 13 September 2023 14:20
> >>> To: [e-mail]; Ingemar Johansson S
> >>> <[e-mail]>
> >>> Cc: [e-mail]; [e-mail]; [e-mail];
> >>> [e-mail]; [e-mail]; [e-mail];
> >>> [e-mail]; [e-mail]; [e-mail];
> >>> [e-mail]; [e-mail]; [e-mail]
> >>> Subject: AW: [tsvwg] [iccrg] New Internet Draft: Congestion Signaling
> >>> (CSIG)
> >>>
> >>> Hi Ingemar, hi Sebastian,
> >>>
> >>> Skimming over the draft only, isn't CSIG about Ethernet-domains,
> >>> while L4S is E2E?
> >>>
> >>> Regards,
> >>>
> >>> Ruediger
> >>>
> >>> -----Ursprüngliche Nachricht-----
> >>> Von: tsvwg <[e-mail]> Im Auftrag von Sebastian Moeller
> >>> Gesendet: Mittwoch, 13. September 2023 13:42
> >>> An: Ingemar Johansson S
> >>> <ingemar.s.johansson=[e-mail]>
> >>> Cc: Vidhi Goel <vidhi_goel=[e-mail]>;
> >>> Shihang(Vincent) <shihang9=[e-mail]>; tsvwg
> >>> <[e-mail]>; Jai Kumar <[e-mail]>; IETF IPPM WG
> >>> <[e-mail]>; Tom Herbert <tom=[e-mail]>;
> >>> [e-mail]; Abhiram Ravi <abhiramr=[e-mail]>;
> >>> Nandita Dukkipati <[e-mail]>; [e-mail]; Huangyihong
> >>> (Rachel) <rachel.huang=[e-mail]>; Naoshad Mehta
> >>> <[e-mail]>
> >>> Betreff: Re: [tsvwg] [iccrg] New Internet Draft: Congestion Signaling
> >>> (CSIG)
> >>>
> >>> Hi Ingemar,
> >>>
> >>>
> >>>> On Sep 13, 2023, at 12:30, Ingemar Johansson S
> >>> <ingemar.s.johansson=[e-mail]> wrote:
> >>>>
> >>>> Hi
> >>>>
> >>>> I agree with Vihdi
> >>>>
> >>>> L4S is recently standardised
> >>>
> >>>     [SM] In experimental track, the goal is currently to test whether
> it
> >>> can/should be deployed at scale....
> >>>
> >>>> and it is definitely gaining traction also in 3GPP. We have an echo
> >>> system that is looking forward to having L4S widely deployed.
> >>>> Still, the congestion control aspects are not fully explored yet.
> >>>> One
> >>> interesting topic is if L4S allows to more safely deviate from
> >>> additive increase to make congestion control algorithms more quickly
> >>> converge to higher link capacity. There are a number of study topics
> >>> around L4S congestion control that are listed in e.g the TCP Prague
> draft.
> >>>>
> >>>> I cannot dictate what others should do with their time and money but
> >>> personally I'd prefer that the IETF explores L4S and its
> >>> possibilities and downsides before jumping on the next idea.
> >>>
> >>>     [SM] L4S can be described as taking the ideas behind DCTCP and
> >>> making them fit for use over the internet*. Yet the signaling
> >>> discussed here is to be used in e.g. data center contexts where DCTCP
> >>> is already used and found lacking compared to newer methods operating
> >>> on richer congestion information (HPCC, Swift, Poseidon, ...).
> >>>     Given that L4S essentially uses a multi-packet signal(**) to
> report
> >>> the "queue filling state" that is then stochastically distributed
> >>> over all concurrent flows, it seems obvious to me that reconstructing
> >>> a reliable estimate of on-path queueing will take some time and
> >>> averaging for each individual flow, I would guess that in some
> >>> environments this delay simply is too costly.
> >>>     So L4S and CSIG seem complementary and in no way mutually
> exclusive.
> >>>
> >>>
> >>> Regards
> >>>     Sebastian
> >>>
> >>>
> >>>
> >>> *) I will not further discuss whether that is achieved or not as it
> >>> seems irrelevant here.
> >>> **) In essence transmission of congestion state via a 1-bit serial
> >>> channel, clocked at the (variable***) packet rate at the bottleneck.
> >>> ***) as packets are not of uniform size
> >>>
> >>>>
> >>>> CSIG sounds to me like something that belongs more in ICCRG or ?
> >>>>
> >>>> /Ingemar
> >>>>
> >>>> From: tsvwg <[e-mail]> On Behalf Of Vidhi Goel
> >>>> Sent: Wednesday, 13 September 2023 00:59
> >>>> To: Shihang(Vincent) <shihang9=[e-mail]>
> >>>> Cc: Huangyihong (Rachel) <rachel.huang=[e-mail]>;
> >>> Tom Herbert <tom=[e-mail]>; Abhiram Ravi
> >>> <abhiramr=[e-mail]>; IETF IPPM WG <[e-mail]>;
> >>> tsvwg <[e-mail]>; [e-mail]; [e-mail]; Nandita
> >>> Dukkipati <[e-mail]>; Naoshad Mehta <[e-mail]>;
> >>> Jai Kumar <[e-mail]>
> >>>> Subject: Re: [tsvwg] [iccrg] New Internet Draft: Congestion
> >>>> Signaling
> >>> (CSIG)
> >>>>
> >>>> Not sure why we are coming up with so many new techniques when ECN
> >>> just works fine.
> >>>> ECN is a 2 bit field (not 1 bit) and seems to be sufficient to
> >>> indicate extent of congestion by marking it per packet. Adding more
> >>> complexity to any layer whether it is L2 or L3 doesn’t work well in
> >>> deployments. Our goal should be to simplify things and only add new
> >>> headers if absolutely necessary.
> >>>>
> >>>> Vidhi
> >>>>
> >>>>
> >>>> On Sep 12, 2023, at 3:12 AM, Shihang(Vincent)
> >>> <shihang9=[e-mail]> wrote:
> >>>>
> >>>> Hi,
> >>>> I agree L2 may not be the best choice to carry the congestion
> >>> signaling end-to-end and more bits are needed. We have submitted a
> >>> draft to carry the multi-bits congestion signaling in L3. We call it
> >>> Advanced ECN. See
> https://datatracker.ietf.org/doc/draft-shi-ccwg-advanced-ecn/.
> >>>>
> >>>> Thanks,
> >>>> Hang
> >>>>
> >>>> From: CCWG <[e-mail]> On Behalf Of Huangyihong (Rachel)
> >>>> Sent: Tuesday, September 12, 2023 5:41 PM
> >>>> To: Tom Herbert <tom=[e-mail]>; Abhiram Ravi
> >>> <abhiramr=[e-mail]>
> >>>> Cc: IETF IPPM WG <[e-mail]>; tsvwg <[e-mail]>;
> >>> [e-mail]; [e-mail]; Nandita Dukkipati
> >>> <[e-mail]>; Naoshad Mehta <[e-mail]>; Jai Kumar
> >>> <[e-mail]>
> >>>> Subject: Re: [CCWG] [iccrg] [tsvwg] New Internet Draft: Congestion
> >>> Signaling (CSIG)
> >>>>
> >>>> Hi,
> >>>>
> >>>> I also have the same feeling. Implementing in L2 may be difficult to
> >>> be used in e2e transport. Of course it can work well in limited
> >>> domain, like DC or HPC clusters. However, I also look for some
> >>> solutions that could be able to go through internet. We have
> >>> submitted a draft to describe the transport challenges. See
> >>> https://datatracker.ietf.org/doc/html/draft-huang-tsvwg-transport-
> >>> challenges.
> >>>>
> >>>> I share the same opinion that the congestion signal is useful and
> >>> current 1-bit ECN solution is not fully sufficient. But I also feel
> >>> like the more straight way is to extend L3, or l4, like update IOAM,
> >>> to carry the information. For L2 solution, it should be developed
> >>> together with IEEE 802.1.
> >>>>
> >>>> BR，
> >>>> Rachel
> >>>>
> >>>> 发件人: iccrg <[e-mail]> 代表 Tom Herbert
> >>>> 发送时间: 2023年9月10日 0:10
> >>>> 收件人: Abhiram Ravi <abhiramr=[e-mail]>
> >>>> 抄送: IETF IPPM WG <[e-mail]>; tsvwg <[e-mail]>;
> >>> [e-mail]; [e-mail]; Nandita Dukkipati
> >>> <[e-mail]>; Naoshad Mehta <[e-mail]>; Jai Kumar
> >>> <[e-mail]>
> >>>> 主题: Re: [iccrg] [tsvwg] New Internet Draft: Congestion Signaling
> >>> (CSIG)
> >>>>
> >>>> Hi, thanks for draft!
> >>>>
> >>>> The first thing that stands out to me is the carrier of the new
> >>>> packet
> >>> headers. In the forward path it would be in L2 and in reflection it
> >>> would be L4. As the draft describes, this would entail having to
> >>> support the protocol in multiple L2 and multiple L4 protocols--
> >>> that's going to be a pretty big lift! Also, L2 is not really an
> >>> end-to-end protocol (would legacy switches in the path also forward
> the header)l?).
> >>>>
> >>>> The signaling being described in the draft is network layer
> >>> information, and hence IMO should be conveyed in network layer headers.
> >>> That's is L3 which conveniently is the average of L2+L4 :-)
> >>>>
> >>>> IMO, the proper carrier of the signal data is Hop-by-Hop Options.
> >>>> This
> >>> is end-to-end and allows modification of data in-flight. The typical
> >>> concern with Hop-by-Hop Options is high drop rates on the Internet,
> >>> however in this case the protocol is explicitly confined to a limited
> >>> domain so I don't see that as a blocking issue for this use case.
> >>>>
> >>>> The information being carried seems very similar to that of IOAM
> >>>> (IOAM
> >>> uses Hop-by-Hop Options and supports reflection). I suppose the
> >>> differences are that this protocol is meant to be consumed by the
> >>> transport Layer and the data is a condensed summary of path
> >>> characteristics. IOAM seems pretty extensible, so maybe it could be
> >>> adapted to carry the signals of this draft?
> >>>>
> >>>> A related proposal might be FAST draft-herbert-fast. Where the CSIG
> >>>> is
> >>> network to host signaling, FAST is host to network signaling for the
> >>> purposes of requesting network services. These might be complementary
> >>> and options for both may be in the same packet. FAST also uses
> >>> reflection, so we might be able to leverage some common
> >>> implementation at a destination.
> >>>>
> >>>> Tom
> >>>>
> >>>> On Fri, Sep 8, 2023, 7:43 PM Abhiram Ravi
> >>> <abhiramr=[e-mail]> wrote:
> >>>> Hi IPPM folks,
> >>>>
> >>>> I am pleased to announce the publication of a new internet draft,
> >>> Congestion Signaling (CSIG): https://datatracker.ietf.org/doc/draft-
> >>> ravi-ippm-csig/
> >>>>
> >>>> CSIG is a new end-to-end packet header mechanism for in-band
> >>>> signaling
> >>> that is simple, efficient, deployable, and grounded in concrete use
> >>> cases of congestion control, traffic management, and network
> >>> debuggability. We believe that CSIG is an important new protocol that
> >>> builds on top of existing in-band network telemetry protocols.
> >>>>
> >>>> We encourage you to read the CSIG draft and provide your feedback
> >>>> and
> >>> comments. We have also cc'd the TSVWG, CCWG, and ICCRG mailing lists,
> >>> as we believe that this work may be of interest to their members as
> well.
> >>>>
> >>>> Thank you for your time and consideration.
> >>>>
> >>>> Sincerely,
> >>>> Abhiram Ravi
> >>>> On behalf of the CSIG authors
> >>
> >
> > _______________________________________________
> > iccrg mailing list
> > [e-mail]
> > https://www.irtf.org/mailman/listinfo/iccrg
>
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