Re: [tsvwg] 回复：Takeaways for HPCC++

["Scharf, Michael" <[e-mail]>]

RFC 6077 Section 3.1 summarizes challenges for all congestion control schemes that rely on network support known at the time of publicatiob.

In addition to the general issues, RFC 6077 Section 3.1 also includes some specific literature pointers to known issues for XCP. As far as I recall, some of the issues in XCP were fairly fundamental. The corresponding papers are referenced in the RFC.

Before publication of RFC 6077, I have myself worked with XCP simulations and XCP hardware implementations. In my PhD thesis I have compared, amonst others, XCP with a simpler solution developed in the IETF (Quick-Start). My personal findings can be found in Sections 4, 5 and 6 of my Phd thesis:

http://content.ikr.uni-stuttgart.de/Content/Publications/Archive/Sf_Diss_40112.pdf

Specifically, I ran into issues when a router supporting XCP cannot correctly determine the capacity of a link (see section 6.5.3.3 in the thesis).

RFC 6077 explains why it is not trivial to actually know what link capacity in reality (i.e., outside simulations). Examples for such cases include virtualization, tunneling, brownfield deployments with legacy devices, etc.

I don’t understand HPCC++ well enough to know how this problem is solved in actual deployments. If you want to repeat the experiment I did in my PhD thesis for XCP (cf. Section 6.5.3.3), you would have to run e.g. experiments in which the actual link capacity is either by factor 10 larger or by factor 10 smaller than the capacity assumed in the algorithm (I guess it is the variable B_j in the draft). If a congestion control algorithm shall be robust, IMHO it would have to be able to deal with such situations. According to my own results, XCP did not work well in such cases of capacity over- or under-estimation.

BTW, the I-D „draft-irtf-panrg-what-not-to-do“ also discusses related lessons learnt.

Michael


From: Richard Li <[e-mail]>
Sent: Monday, November 2, 2020 1:44 AM
To: Scharf, Michael <[e-mail]>; Rui, Miao <[e-mail]>; tsvwg <[e-mail]>
Cc: Barak Gafni <[e-mail]>; tsvwg-chairs <[e-mail]>
Subject: RE: [tsvwg] 回复：Takeaways for HPCC++

> it is has specifically taken into account lessons learnt from protocols such as XCP

Would you mind sharing what lessons exactly you learnt from XCP?

Thanks,

Richard




From: tsvwg <[e-mail]<mailto:[e-mail]>> On Behalf Of Scharf, Michael
Sent: Wednesday, October 28, 2020 10:48 AM
To: Rui, Miao <[e-mail]<mailto:[e-mail]>>; tsvwg <[e-mail]<mailto:[e-mail]>>
Cc: Barak Gafni <[e-mail]<mailto:[e-mail]>>; tsvwg-chairs <[e-mail]<mailto:[e-mail]>>
Subject: Re: [tsvwg] 回复：Takeaways for HPCC++

Hi all,
An editorial comment: ICCRG has published RFC 6077 about ten years ago. Obviously, the document may be a bit dated, but it is has specifically taken into account lessons learnt from protocols such as XCP or Quick-Start. Not all content of RFC 6077 may apply to current data centers. Nonetheless, some of the content in RFC 6077 is quite generic, and it could be useful to better explain in a description of HPC++ how this architecture addresses the challenges.
Best regards
Michael (as co-author of RFC 6077)

From: tsvwg <[e-mail]<mailto:[e-mail]>> On Behalf Of Rui, Miao
Sent: Friday, September 11, 2020 10:53 AM
To: Miao, Rui(缪睿) <[e-mail]<mailto:[e-mail]>>; tsvwg <[e-mail]<mailto:[e-mail]>>
Cc: Barak Gafni <[e-mail]<mailto:[e-mail]>>; tsvwg-chairs <[e-mail]<mailto:[e-mail]>>
Subject: [tsvwg] 回复：Takeaways for HPCC++

Dear WG members,

At IETF 108, we presented HPCC++, a new architecture for congestion control designed for high-speed networks. We have modified the draft according to the feedback from the meeting. The newer version is available at https://tools.ietf.org/html/draft-pan-tsvwg-hpccplus-02<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-pan-tsvwg-hpccplus-02&data=04%7C01%7Crichard.li%40futurewei.com%7C5f95b2910d2b41a59fe208d87b699b9a%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C1%7C637395040817739023%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=Q%2FDwV%2Bm73NlD3m%2BmYoOIA0OGUUlgtUYCUFz2uwAC3Qk%3D&reserved=0>

Thanks, and please feel free to let us know if you have more comments.

Thanks,
Rui

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发件人：Miao, Rui(缪睿) <[e-mail]<mailto:[e-mail]>>
发送时间：2020年8月2日(星期日) 11:21
收件人：tsvwg <[e-mail]<mailto:[e-mail]>>
抄　送：tsvwg-chairs <[e-mail]<mailto:[e-mail]>>; Wesley Eddy <[e-mail]<mailto:[e-mail]>>; "Pan, Rong" <[e-mail]<mailto:[e-mail]>>; Barak Gafni <[e-mail]<mailto:[e-mail]>>
主　题：Takeaways for HPCC++


Hello TSVWG members,

It was our pleasure to present HPCC++ in the IETF-108 meeting this week. We appreciate your valuable feedback. Our current draft is located at https://tools.ietf.org/html/draft-pan-tsvwg-hpccplus-01<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-pan-tsvwg-hpccplus-01&data=04%7C01%7Crichard.li%40futurewei.com%7C5f95b2910d2b41a59fe208d87b699b9a%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C1%7C637395040817748978%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=mrAKAuPvwwdWCBghjQDoMYqNftztOQtCmGJivkqwgpE%3D&reserved=0>.
Here, we have summarized a list of takeaways to further improve the draft.

1. HPCC++ is a generic congestion control scheme that works for high-speed networks. It requires to have window limit and ACK self-clocking, which is out of the definition of RoCEv2 but should instead work well for TCP/iWRAP. In addition, HPCC++ conforms to the paradigm of existing TCP congestion control, such as switch marking, receiver feedback, and sender enforcement. The major changes are using inband telemetry as the congestion feedback and it is incremental. In the next revision, we describe clearly how it works for TCP/UDP and related protocols.

2. HPCC++ works for both data centers and the Internet. We will add descriptions and results for the Internet-scale size and latency in the next revision.

Thanks again for the comments. Please feel free to let us know if you have more thoughts.

All the best,
Rui, Rong, Barak