[e2e] TCP ex Machina
Alexander.Zimmermann at netapp.com
Sun Jul 28 11:43:44 PDT 2013
Am 26.07.2013 um 19:44 schrieb Joe Touch <touch at ISI.EDU>:
> Hi, Jon,
> On 7/25/2013 9:53 PM, Jon Crowcroft wrote:
>> I'm sorry, but this smacks of "orthodoxy"
>> which is anathema to good science.
> I'm not referring to science, or research. I'm referring to changes to TCP that are being pushed for deployment or already deployed.
> E.g., TCP-CT is not an approved IETF standard. It was not taken to through the IETF process. But it is *deployed* in Linux.
Fortunately, TCP-CT is not part of Linux anymore.
> As an example of bad behavior, TCP-CT uses a TCP option codepoint that is reserved for experiments that are not widely deployed.
>> the reality is that the nature of
>> most of the "optimization" work that makes it into good conferences
>> (nsdi, icnp, sigcomm, pick your fave)
>> are in the nature of the word you use - extensions
> There are different kinds of TCP extensions, falling into at least two broad categories:
> A- extensions to TCP itself
> A1- some intended to make TCP more robust or address
> a corner case
> A2- some intended to correct a problem in TCP's design
> A3- some intended to support a specific use case
> B- using the TCP protocol ID and coarsely conforming to TCP's
> connection establishment
> I'm not referring to A1 or A2, which includes some published research.
> I'm concerned more about B, and somewhat about A3.
> B-style extensions are really new transport protocols. That's a valid area of research, but the deployment reality is that no such new transports can traverse widely-deployed non-standard network elements (e.g., NATs). So B is really a new transport masquerading as TCP.
> A3 are extensions to optimize specific use cases. The trouble with such optimizations is that they can easily undermine a key feature of TCP - that it falls back to working nearly all the time it possibly can.
> I don't consider breaking that key property of TCP a good thing.
> Experimentation is fine, as is research. But the medical community doesn't start playing with new meds by handing them out on street corners like candy.
>> so of course there might be extensions which would kick in,
>> in the wrong circumstances and do harm -
>> so do you believe any OS vendor or
>> community would ship those?
> Linux. Cisco. Alcatel-Lucent. This is a partial list of vendors who have deployed code that uses *the same* experimental codepoint.
>> do you believe that unless the papers about them showed a net win,
>> anyone would use them?
> Yes. Linux has done this repeatedly.
>> instead of waiting a duty cycle of 1 grad-student-year for a next
>> TCP congestion control idea,
>> you use a big cluster of machines and evolutionary computing
>> to run at the rate of around 100 graduate students-per-week
>> and pick the best according to some metric -
>> you could, if you like, pick a different metric
> I did, and you took issue with it.
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