Re: [p2pi] Information in an ALTO protocol

On Sep 15, 2008, at 7:54 AM, Laird Popkin wrote:

> The cost of bandwidth testing isn't terrible, but the accuracy of  
> measurements taken on 1K transfers is very low - you're really  
> measuring latency and buffering, not sustained data transfer rate.  
> Of course, there might be some relationship between them, but (at  
> least in our measurements) it took much larger data transfers to get  
> even remotely stable results. In addition, measuring actual  
> throughput at a point in time can be affected by other traffic on  
> the PC (e.g. PC's do many things when they're starting up), other  
> nearby PC's (e.g. someone else in your neighborhood is busy right  
> now), transient interference on the internet, etc. So while it's not  
> unreasonable to do such testing, and we certainly do so, an ISP  
> provided provisioned capacity would be much more accurate (when it's  
> available).

The point of the 1K back-to-back packets is NOT that you are testing  
the transfer time for the 1K packets, but that interarrival time of  
the packets can be used as an uncongested-link bandwidth estimate, as  
long as the queue at the point of congestion uses FIFO delivery of  
packets.

Since the question you are asking the user is "whats the UNCONGESTED"  
behavior as a starting point (to set an initial threshold/ceiling  
somewhere below this point), the behavior of back-to-back packets  
should get you in the right ballpark without having to ask the user.

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