[R-C] Simplifying the TCP throughput algorithm

[Luca De Cicco]

Dear Harald,

it's not that safe modifying the PFTK formula without breaking
tcp-friendliness (if we want to be tcp-friendly, and I assume we want
it).  That formula mimics the long term behaviour of a TCP flow
experiencing a specific RTT and packet loss ratio p.
Not taking into account the RTT of the connection to estimate TCP
throughput is quite dangerous.

Cheers,
Luca


On Thu, Mar 29, 2012 at 1:07 PM, Ali C. Begen (abegen) <abegen at cisco.com> wrote:
> I suppose these were random losses?
>
>> -----Original Message-----
>> From: rtp-congestion-bounces at alvestrand.no [mailto:rtp-congestion-bounces at alvestrand.no] On Behalf Of Harald
>> Alvestrand
>> Sent: Thursday, March 29, 2012 1:04 PM
>> To: rtp-congestion at alvestrand.no
>> Subject: [R-C] Simplifying the TCP throughput algorithm
>>
>> I did some extremely rough numerical experiments with the TCP throughput
>> algorithm.
>>
>> Results for TCP throughput in bits/sec at MSS=1440 bytes at various loss
>> rates:
>>
>> 0.001% loss: Throughput 4.5 Mbits/sec (HD can survive)
>> 0.01% loss: Throughput 1.4 Mbits/sec
>> 0.1% loss: Throughput 458 Kbits/sec (VGA can survive)
>> 1% loss: Throughput 144 Kbits/sec (good audio can survive)
>> 10% loss: Throughput 43 Kbits/sec (crappy audio can survive)
>>
>> These are stable in the first 2 digits over a large range of RTT (1 ms
>> to 100 ms).
>>
>> Interesting numerical result: In all cases, the second term of the TCP
>> throughput denominator is less than 1% of the first term, so a
>> reasonable approximation is:
>>
>> T = s / sqrt(p * 2/3)
>>
>> That's a simple formula.
>>
>>                   Harald
>>
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