[Bloat] Goodput fraction w/ AQM vs bufferbloat

[Richard Scheffenegger]

Note that this will only give you a lower bound; the true losses that were 
addressed by the sender (ie. RTO retransmissions that got lost again) can by 
principle not be discovered by a receiver side trace, only a (reliable) 
sender side trace will allow that.

To the second point: Only for simple Reno/NewReno there exists a closed 
formular for estimating throughput based on random, non-markow distributed 
losses; and more modern congestion control / loss recovery scheme will 
permit (more or less slightly) higher thoughput, thus the formulas (ie. RFC 
3448 states the one for Reno) will only serve as a (good) lower bound 
estimate.

Again, increasing throughput at the cost of goodput is a bad proposition, if 
you get charged by traffic volume (because what you really want is data 
delivered to the receiver, not dumped into the network for no good reason).

Regards,
   Richard


----- Original Message ----- 
From: "Fred Baker" <fred at cisco.com>
To: "richard" <richard at pacdat.net>
Cc: <bloat at lists.bufferbloat.net>
Sent: Friday, May 06, 2011 11:56 PM
Subject: Re: [Bloat] Goodput fraction w/ AQM vs bufferbloat


>
> On May 6, 2011, at 8:14 AM, richard wrote:
>> If every packet takes two attempts then the ratio will be 1/2 - 1 unit
>> of googput for two units of throughput (at least up to the choke-point).
>> This is worst-case, so the ratio is likely to be something better than
>> that 3/4, 5/6, 99/100 ???
>
> I have a suggestion. turn on tcpdump on your laptop. Download a web page 
> with lots of imagines, such as a google images web page, and then download 
> a humongous file. Scan through the output file for SACK messages; that 
> will give you the places where the receiver (you) saw losses and tried to 
> recover from them.
>
>> Putting a number to this will also help those of us trying to get ISPs
>> to understand that their Usage Based Bilking (UBB) won't address the
>> real problem which is hidden in this ratio. The fact is, the choke point
>> for much of this is the home router/firewall - and so that 1/2 ratio
>> tells me the consumer is getting hosed for a technical problem.
>
> I think you need to do some research there. A TCP session with 1% loss 
> (your ratio being 1/100) has difficulty maintaining throughput; usual TCP 
> loss rates are on the order of tenths to hundredths of a percent.
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