[Iccrg] Initial value of dwnd

[Saverio Mascolo]

we have tested newreno (only ietf standard), bic (linux default), cubic and
westwood+ over commercial hsdpa card. we run 3000 experiments (down and up
links).
main results were:
1. similar downlink goodputs but with much more timeouts and packet loss
ratio when using bic/cubic (3 times timeouts and 2 times packet loss ratio)
2. larger rtt experienced when using bic/cubic


also cwnd dynamics do not look great!

more details can be found at:

http://c3lab.poliba.it/index.php/TCP_over_Hsdpa

saverio

On Fri, Nov 14, 2008 at 8:58 AM, denis.collange <
denis.collange at orange-ftgroup.com> wrote:

>
> Hello,
>
> We have a question concerning the Compound TCP draft, along the lines of
> point 4 in *
> http://oakham.cs.ucl.ac.uk/pipermail/iccrg/2008-March/000468.html*<http://oakham.cs.ucl.ac.uk/pipermail/iccrg/2008-March/000468.html>("4. What happens to dwnd during slow-start, and when is slow-start
> exited?")
>
> The draft states that "dwnd is initialized to zero while the connection is
> in slow start" (p. 6), and then "Delay-based component only kicks in when
> cwnd is larger than some threshold, currently set to 38 packets assuming
> 1500 byte MTU" (p.11).
>
> However, starting from zero, the recursion (3) on p. 7 gives a negative
> value, so that dwnd would always be set to 0. In order for dwmd to be
> positive the initial value needs to be such that:
>
>         alpha*dwnd(t)^k - 1 > 0
> (if dwnd is restricted to integer values a larger initial value might be
> needed depending on how the rounding is done).
>
> Clearly an initial value of 38 does satisfy this requirement but it is not
> clear whether this is the initial value that should be assigned to dwnd
> after slow-start or when the cwnd is larger then the specified threshold (38
> in the draft).
>
> We think that the draft should clearly state the initial value for dwnd
> every time the delay component is activated.  It might also be interesting
> to comment on why the window update function is not the same as in the
> previously published papers about Compound TCP.
>
> Thanks,
>
> Denis and Alberto
>
>
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> Iccrg at cs.ucl.ac.uk
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>
>


-- 
Prof. Saverio Mascolo
Dipartimento di Elettrotecnica ed Elettronica
Politecnico di Bari
Via Orabona 4
70125 Bari
Italy
Tel. +39 080 5963621
Fax. +39 080 5963410
email:mascolo at poliba.it <email%3Amascolo at poliba.it>

http://www-dee.poliba.it/dee-web/Personale/mascolo.html


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-- 
Prof. Saverio Mascolo
Dipartimento di Elettrotecnica ed Elettronica
Politecnico di Bari
Via Orabona 4
70125 Bari
Italy
Tel. +39 080 5963621
Fax. +39 080 5963410
email:mascolo at poliba.it <email%3Amascolo at poliba.it>

http://www-dee.poliba.it/dee-web/Personale/mascolo.html


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