[UDT] Re: Meaning of m_issthresh

[Harald s. <sc...@rv...>]

Hi Yunhong,
thank you very much for your quick respond. This make sence.
I'm slowly beginning to understand how UDT's CCC work.
By,
Harald



Am Montag, den 13.03.2006, 10:51 -0600 schrieb Yunhong Gu:
> Harald,
>=20
> YOu are right. I was assuming an infinite ssthresh at the beginning but=
=20
> forgot to check it in the later slow start phases.
>=20
> The ACKAction() should like this:
>     virtual void ACKAction()
>     {
>        if (m_bSlowStart)
>        {
>           m_dCWndSize +=3D 1.0;
>=20
>           if (m_dCWndSize >=3D m_issthresh)
>              m_bSlowStart =3D false;
>        }
>        else
>           m_dCWndSize +=3D 1.0/m_dCWndSize;
>     }
>=20
> and the initial m_issthresh should be a large value.
>=20
> Thanks
> Yunhong
>=20
>=20
> On Mon, 13 Mar 2006, Harald schwier wrote:
>=20
> > Hello Yunhong,
> > Thank you for your answer.
> > I've transfered 10GB of data in our testnet. The router is configured
> > to create a delay off 100ms and to drop every 1000000 Paket.
> >
> > Slow start should double the congestion window every RTT until it
> > reaches ssthresh. Because of  m_issthresh =3D 2; (cc.h line 34) i
> > expected that UDT-tcp did not perform slow start at the beginning
> > of the connection. But the measurement shows that the connection
> > performs slow start. Have i misunderstood the meaning of m_issthresh?
> >
> > I've attached the measured data transfer.
> > Bye,
> >
> >
> > Am Freitag, den 10.03.2006, 14:14 -0600 schrieb Yunhong Gu:
> >> Hi, Harald,
> >>
> >> Thanks for your comment.
> >>
> >> In CTCP, your connection probably didn't see any packet loss, so the=
 cwnd
> >> simply continue to increase with slow start. Can you verify this?
> >>
> >> You are right about the Scalable TCP implementation, after 38, it st=
ill
> >> needs slow start. I have fixed this and will update the CVS soon.
> >>
> >> Thanks
> >> Yunhong
> >>
> >> On Fri, 10 Mar 2006, Harald schwier wrote:
> >>
> >>> Hello,
> >>> i'm a little unsecure about the meaning of the value "m_issthresh",
> >>> which is initialized in cc.h ( class CTCP ). I thought that it is
> >>> the initial slow start threshhold, but although it is initialized
> >>> with "2", udt (ccc CTCP) performs slow start up to an arbitrary
> >>> high congestion window.
> >>>
> >>> Second, udt is very slow if i use UDT-scalable (high RTT).
> >>> UDT-Scalable uses TCP at a Congestion Window below 38.
> >>> After that it updates the congestion window according to CW=3DCW+0.=
01,
> >>> which means a very slow increase at low Congestion Windows (That's =
why
> >>> scalable is called scalable :-) ). At a RTT of 100ms UDT-scalable
> >>> needs 120 seconds to fully utilise a Gigabit Link.
> >>> I think that scalable should perform slow start after the connectio=
n is
> >>> established.
> >>>
> >>> Third, I think that UDT is GREAT WORK!!!
> >>>
> >>> Bye,
> >>> Harald
> >>>
> >>>
> >>>
> > Mit freundlichen Gr=C3=BC=C3=9Fen,
> > Harald Schwier
> >
> >
> > --=20
> > Dipl.-Ing. Harald Schwier          D-30159 Hannover
> > Lehrgebiet Rechnernetze            Schlosswender Str. 5
> > RRZN, Universit=C3=A4t Hannover         Tel: +49 (511) 762 7919081
> > Fachbereich Informatik
> >
> >
> >
Mit freundlichen Gr=C3=BC=C3=9Fen,
Harald Schwier


--=20
Dipl.-Ing. Harald Schwier          D-30159 Hannover
Lehrgebiet Rechnernetze            Schlosswender Str. 5
RRZN, Universit=C3=A4t Hannover         Tel: +49 (511) 762 7919081
Fachbereich Informatik