Re: [p2pi] Refining the ALTO problem statement [Was: Re: discussing P2PI-related standardization in Dublin]

Hi,

On 2008-6-18, at 5:29, ext Henning Schulzrinne wrote:
> I do see a need for standardization here, namely conveying the  
> current bandwidth price or total usage. (More complicated models are  
> feasible, but I think something pretty simple would do the job and  
> avoid getting into business models.)
>
> You'd want to get something like
>
> "Your current charge for priority X is Y currency units/byte, valid  
> until time T."
>
> "You have used B bytes out of L bytes for priority X."
>
> "Your max. rate for priority X is S bits/second."
>
> This covers the major knobs that a provider can turn (quotas, rate  
> limits and metering).

that seems reasonable - thanks for clarifying.

>> That is definitely possible. For example, low-RTT peers may be behind
>> other DSL boxes within your ISP, whereas the university with the big
>> pipe is a bit further away in RTT terms than those peers - who'd you
>> like to transfer from? I'd expect the correlation between RTT and
>> transmission time to be pretty weak (but have no data to back this  
>> up.)
>
> Given that TCP throughput is inversely proportional to RTT, one  
> would indeed expect a correlation.

TCP bandwidth is proportional to the RTT when different flows *share  
the same bottleneck*. But that isn't what matters here. Knowing the  
RTT to a potential peer will not allow an app to draw any conclusions  
about projected throughput, because the app knows neither the  
bottleneck capacity nor the RTTs of all other flows going through that  
bottleneck. Plus, the theoretical result is only valid when all flows  
are in steady state.

Lars
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