Re: [re-ECN] preliminary draft of problem statement- authors wanted

[<[e-mail]>]

Thanks for the text. It will give me a good starting point and makes my life easier!

> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On
> Behalf Of João Taveira Araújo
> Sent: 22 September 2009 10:25
> To: [e-mail]
> Subject: Re: [re-ECN] preliminary draft of problem statement- authors
> wanted
> 
> Inline,
> 
> [e-mail] wrote:
> >> I would change "Myoptic Solutions" to "Existing Work". You have
> >> identified two existing ISP solutions: "rate limiting" and "volume
> >> limiting". I would add "simple best effort traffic and flow-rate
> >> fairness" (RFC5290), as well as ECN (RFC3168) with nonces (RFC3540).
> >> You can steal content from sections 3.1.2 and 4.7 of the motivation
> >> draft, of course.
> >>
> >
> > I really wanted a title that conveyed a little more than just
> "existing work". But I agree "myopic" is the wrong word. Will add some
> of those other bits as well. Perhaps I should group them into
> categories (things the network does and things end-systems do?).
> >
> 
> I'm not so sure about using the term "existing work" to refer to ad-
> hoc,
> poorly documented solutions in most cases. They are workarounds, not
> work. Might also want to mention voluntary rate-limiting on the
> end-hosts (p2p apps) as a symptom of dodgy capacity sharing.

I had pondered calling it something truly controversial like "existing failures". Perhaps "existing attempts

> 
> I was hoping for more text before bashing the document, but I assume
> it'll take a while before getting to a semi-finished state. 

I will try and get something a bit longer out in the next day or so to give you more to work on!


I've toyed
> around with a few paragraphs for section 4, but I'm not sure how
> lightweight you want the economics to be. I think the main ideas to get
> across are:
> 
> a) congestion as an externality
> b) congestion as the marginal cost of provisioning network
> c) exposing congestion corrects information asymmetry.

Indeed. My idea is to give the economic concepts in a manner that is quickly intelligible to people with no background in economics

> 
> I'm also unsure whether taking re-ECN out of the picture implies taking
> re-feedback out as well, or whether its the framework we want to have
> for any potential solution. Feel free to pick & mix any of the text,
> I'll be waiting for a future revision to bash.

The idea is to present re-feedback without going into any details. Re-ECN is a special case of re-feedback that requires more understanding. My idea is to say something like "here is re-feedback in an abstract way, this is how it reveals congestion, we have actually implemented it in a real system called re-ECN [see lots of refs for details]"

> 
> Joao.
> 
> 
> 
> 4.  Towards a better solution
> 
>    In the previous section, we have documented how network operators
>    attempt to limit the damage any single user can inflict on others by
>    imposing restrictions on user behaviour.  While these solutions
>    differ in approach, they all attempt to tackle the root cause
>    indirectly by inferring congestion.  To move beyond such shoddy
>    patchwork, there is a need to explicitly treat congestion as a cost.
> 
> 4.1.  Congestion as a cost
> 
>    Congestion is a negative externality - an individual's usage of the
>    network has a negative impact on others.  Unheeded, the ability to
>    inflict congestion on others at no personal cost may lead to a
>    "tragedy of the commons", where self-interested end users undermine
>    the value of the network through selfish behaviour.  Such an extreme
>    case was initially averted due to genuine cooperation through the
>    voluntary deployment of TCP.  As increased commercial pressure is
>    exerted on the Internet however, the assumption that stakeholders
>    will continuously cooperate towards a common goal no longer holds.
> 
>    A possible solution is to apply shadow pricing to the negative
>    externality, effectively forcing individuals to internalise the
> costs
>    they impose on others and therefore holding individuals accountable
>    for their actions.  Kelly [] has shown that charging end-points a
>    shadow price proportional to the congestion they cause leads to the
>    maximization of social welfare.
> 
>    Additionally, shadow pricing plays a dual role, both reflecting the
>    social costs of increased bandwidth usage and the marginal cost of
>    provisioning the network.  As such, adequate resource pricing can be
>    used to recover expansion costs while subscription revenue recovers
>    non-recurring costs.
> 
>    While exerting economic pressure on end-points effectively induces
>    sociable behaviour, retrofitting the Internet with means to enforce
>    congestion pricing has proved elusive.  The best-effort delivery
>    provided by the Internet was built on the assumption that forwarding
>    elements should discard traffic they are unable to service.  While
>    remarkable in its simplicity, this design choice has lead to an
>    Internet which is opaque to failure.  As congestion is viewed end-
> to-
>    end, only end-points hold information on the quality of service
>    provided by the network.  In this case the buyer knows more about
> the
>    product being sold than the seller.  While this is converse to
>    Akerlof's classic examples of information asymmetry [], the outcome
>   is similar, resulting in a suppressed market price which in turn
>    leads to reduced investment in supply.
> 
> (...)
> 
> 4.2.  The limitations of ECN in exposing cost
> 
>    The lack of accountability for congestion was partially addressed
>    with the introduction of ECN [], an explicit marking scheme to
>    indicate the onset of congestion.  While ECN was introduced to
>    maintain networks operating below the point where losses would be
>    experienced, as a side-effect it revealed congestion downstream of
>    the congested link, allowing network devices to quantify congestion
>    without the need for inspecting transport headers.
> 
>    This newfound visibility of congestion was duly exploited by Kelly
>    [].  Using ECN, a network could apply shadow pricing by simply
>    charging the upstream network proportionally to the amount of
>    congestion marked traffic it sent.  Unfortunately, this scheme
> proved
>    impractical and suffers from shortcomings derived from the asymmetry
>    inherent to classic feedback.
> 
>    The fundamental problem with using ECN for congestion pricing is
> that
>    it reveals the correct metric, but to the wrong entities.
>    Intermediate routers can only view congestion ex post and are
>    therefore not only unable to act upon the information provided, but
>    also incapable of verifying its integrity.
> 
> (..)
> 
> 4.3.  Refeedback for congestion exposure
> 
> (...)
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