[Bloat] Researchers discover major roadblock in alleviating network congestion

[Bloat] Researchers discover major roadblock in alleviating network congestion

[Bjørn Ivar Teigen]

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Interesting article from MIT:
https://news.mit.edu/2022/algorithm-computer-network-bandwidth-0804

The paper can be found on Venkat Arun's website:
https://people.csail.mit.edu/venkatar/

Main take-away (as I understand it) is something like "In real-world
networks, jitter adds noise to the end-to-end delay such that any algorithm
trying to infer congestion from end-to-end delay measurements will
occasionally get it wrong and this can lead to starvation". Seems related
to Jaffe's work on network power (titled "Flow control power is
non-decentralizable").

Thoughts?

-- 
Bjørn Ivar Teigen
Head of Research
+47 47335952 | bjorn@domos.no <name@domos.no> | www.domos.no

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Re: [Bloat] Researchers discover major roadblock in alleviating network congestion

[Jonathan Morton]

> On 4 Aug, 2022, at 3:21 pm, Bjørn Ivar Teigen via Bloat <bloat@lists.bufferbloat.net> wrote:
> 
> Main take-away (as I understand it) is something like "In real-world networks, jitter adds noise to the end-to-end delay such that any algorithm trying to infer congestion from end-to-end delay measurements will occasionally get it wrong and this can lead to starvation". Seems related to Jaffe's work on network power (titled "Flow control power is non-decentralizable"). 

Hasn't this been known for many years, as a consequence of experience with TCP Vegas?

 - Jonathan Morton

Re: [Bloat] Researchers discover major roadblock in alleviating network congestion

[Stephen Hemminger]

On Fri, 5 Aug 2022 00:45:12 +0300
Jonathan Morton via Bloat <bloat@lists.bufferbloat.net> wrote:

> > On 4 Aug, 2022, at 3:21 pm, Bjørn Ivar Teigen via Bloat <bloat@lists.bufferbloat.net> wrote:
> > 
> > Main take-away (as I understand it) is something like "In real-world networks, jitter adds noise to the end-to-end delay such that any algorithm trying to infer congestion from end-to-end delay measurements will occasionally get it wrong and this can lead to starvation". Seems related to Jaffe's work on network power (titled "Flow control power is non-decentralizable").   
> 
> Hasn't this been known for many years, as a consequence of experience with TCP Vegas?
> 
>  - Jonathan Morton

It seems like BBR developers thought they could do better. Unfortunately, papers with negative
results never seem to get written or published ;-(

Re: [Bloat] Researchers discover major roadblock in alleviating network congestion

[Daniel Sterling]

"Flow control power is non-decentralizable" is from -- 1981? So we've
known for 40 years that TCP streams won't play nicely with each other
unless you shape them at the slower endpoint-- am I understanding that
correctly? But we keep trying anyway? :)

On Thu, Aug 4, 2022 at 7:24 PM Stephen Hemminger via Bloat
<bloat@lists.bufferbloat.net> wrote:
>
> On Fri, 5 Aug 2022 00:45:12 +0300
> Jonathan Morton via Bloat <bloat@lists.bufferbloat.net> wrote:
>
> > > On 4 Aug, 2022, at 3:21 pm, Bjørn Ivar Teigen via Bloat <bloat@lists.bufferbloat.net> wrote:
> > >
> > > Main take-away (as I understand it) is something like "In real-world networks, jitter adds noise to the end-to-end delay such that any algorithm trying to infer congestion from end-to-end delay measurements will occasionally get it wrong and this can lead to starvation". Seems related to Jaffe's work on network power (titled "Flow control power is non-decentralizable").
> >
> > Hasn't this been known for many years, as a consequence of experience with TCP Vegas?
> >
> >  - Jonathan Morton
>
> It seems like BBR developers thought they could do better. Unfortunately, papers with negative
> results never seem to get written or published ;-(
> _______________________________________________
> Bloat mailing list
> Bloat@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat

Re: [Bloat] Researchers discover major roadblock in alleviating network congestion

[Dave Collier-Brown]

Yup!

My company just decided that routing fallbacks, like the ARPA NIMs had,
weren't necessary. Right after the Rogers BGP fiasco that cut off 50% of
Canada from the internet...

Bother!

--dave

On 8/4/22 19:46, Daniel Sterling via Bloat wrote:
> "Flow control power is non-decentralizable" is from -- 1981? So we've
> known for 40 years that TCP streams won't play nicely with each other
> unless you shape them at the slower endpoint-- am I understanding that
> correctly? But we keep trying anyway? :)
>
> On Thu, Aug 4, 2022 at 7:24 PM Stephen Hemminger via Bloat
> <bloat@lists.bufferbloat.net> wrote:
>> On Fri, 5 Aug 2022 00:45:12 +0300
>> Jonathan Morton via Bloat <bloat@lists.bufferbloat.net> wrote:
>>
>>>> On 4 Aug, 2022, at 3:21 pm, Bjørn Ivar Teigen via Bloat <bloat@lists.bufferbloat.net> wrote:
>>>>
>>>> Main take-away (as I understand it) is something like "In real-world networks, jitter adds noise to the end-to-end delay such that any algorithm trying to infer congestion from end-to-end delay measurements will occasionally get it wrong and this can lead to starvation". Seems related to Jaffe's work on network power (titled "Flow control power is non-decentralizable").
>>> Hasn't this been known for many years, as a consequence of experience with TCP Vegas?
>>>
>>>   - Jonathan Morton
>> It seems like BBR developers thought they could do better. Unfortunately, papers with negative
>> results never seem to get written or published ;-(
>> _______________________________________________
>> Bloat mailing list
>> Bloat@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/bloat
> _______________________________________________
> Bloat mailing list
> Bloat@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat

--
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
dave.collier-brown@indexexchange.com |              -- Mark Twain


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Re: [Bloat] Researchers discover major roadblock in alleviating network congestion

[Jonathan Morton]

> On 5 Aug, 2022, at 2:46 am, Daniel Sterling <sterling.daniel@gmail.com> wrote:
> 
> "Flow control power is non-decentralizable" is from -- 1981? So we've
> known for 40 years that TCP streams won't play nicely with each other
> unless you shape them at the slower endpoint-- am I understanding that
> correctly? But we keep trying anyway? :)

More precisely, what was stated in 1981 was:

The specific metric of "network power" (the ratio of throughput to delay, calculated for each flow and globally summed) cannot reliably be maximised solely by the action of individual endpoints, without information from within the network itself.

Current TCPs generally converge not to maximise or even equalise "network power", but to equalise between flows a completely different metric called "RTT fairness", the *product* of throughput and delay.  Adding information from the network via AQMs allows for reductions in delay with little effect on throughput, and thus a general increase in network power, but the theoretical global optimum is still not even approached.

Adding FQ in the network, thus implementing "max-min fairness" instead of "RTT fairness", hence equalising throughput instead of the product of throughput and delay.  This is essentially the geometric mean of RTT-fairness and network power.

I believe it is actually possible to achieve equalisation of network power between flows, which would approach the global optimum of network power, using information from the network to guide endpoint behaviour.  This is *only* possible using explicit information from the network, however, and is not directly compatible with the current congestion-control paradigm of RTT-fairness by default.

 - Jonathan Morton

Re: [Bloat] Researchers discover major roadblock in alleviating network congestion

[Michael Richardson]

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Jonathan Morton via Bloat <bloat@lists.bufferbloat.net> wrote:
    > I believe it is actually possible to achieve equalisation of network
    > power between flows, which would approach the global optimum of network
    > power, using information from the network to guide endpoint behaviour.
    > This is *only* possible using explicit information from the network,
    > however, and is not directly compatible with the current
    > congestion-control paradigm of RTT-fairness by default.

There is a thread on ietf@ietf.org about the role of the IETF (and RFCs) in
making the Internet more sustainable/energy efficient.

I don't think that the term "network power" is units of Joules :-)
but I do think that transmitters that are fully powered on, but idle are a waste.
I think that we (the world/internet/R&D/operational community) are ready for
ways to optimize flows that explicitely take information from the network.

To do this well requires new trust relationships that have been very
difficult to even create locally, even within an Enterprise.


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