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

[Ingemar Johansson S <[e-mail]>]

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 ? 

/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