Re: [tcpm] TCP tuning

> -----Original Message-----
> From: Jerry Chu [mailto:hkchu@google.com] 
> Sent: Wednesday, February 03, 2010 10:21 AM
> To: Michael Welzl
> Cc: tcpm@ietf.org WG
> Subject: Re: [tcpm] TCP tuning
> 
> 
> Michael,
> 
> On Wed, Feb 3, 2010 at 6:42 AM, Michael Welzl 
> <michawe@ifi.uio.no> wrote:
> > Hi all,
> >
> > (sorry if this is a bit off topic, as the mentioned presentation is 
> > mainly about using a larger initial window)
> >
> > In the context of the discussion that Jerry brought up on parameter 
> > tuning, one question that was raised was the initial RTO during the 
> > SYN - SYN/ACK exchange. I understand that we can't 
> recommend to resend 
> > SYN's more aggressively because this might cause a server to be 
> > overloaded with SYN's, but why do we have to wait extremely 
> long until 
> > we resend SYN/ACKs?
> >
> > Back then, when I asked, I got no answer. Both Jerry and I 
> pointed to 
> > our measurement results which show that the effect is nonneglible.
> 
> Actually Mark Allman, Vern Paxon and I have been working on 
> revising RFC2988 to reduce the initial RTO from 3secs to 
> 1sec. Will submit the proposal soon!
> 
This implies that this proposal brings the intial RTO value to be equal to the minimum RTO value of 1 second. Is this true? 

I am going by RFC 2988, section 2, 2.4. It explicitly states this:

" (2.4) Whenever RTO is computed, if it is less than 1 second then the
         RTO SHOULD be rounded up to 1 second.

         Traditionally, TCP implementations use coarse grain clocks to
         measure the RTT and trigger the RTO, which imposes a large
         minimum value on the RTO.  Research suggests that a large
         minimum RTO is needed to keep TCP conservative and avoid
         spurious retransmissions [AP99].  Therefore, this
         specification requires a large minimum RTO as a conservative
         approach, while at the same time acknowledging that at some
         future point, research may show that a smaller minimum RTO is
         acceptable or superior."

Is it time to reconsider a smaller minimum RTO as well? 

> Best,
> 
> Jerry
> 
> >
> > So I'll use this chance to ask again  :-)
> >
> > Cheers,
> > Michael
> >
> >
> > On Feb 3, 2010, at 3:28 PM, Lars Eggert wrote:
> >
> >> Hi,
> >>
> >> Jerry Chu has recently started the discussion on whether 
> we need to 
> >> think about tweaking TCP for the "modern Internet." Just 
> came across 
> >> another presentation from (AFAICT) another corner of Google that 
> >> makes similar arguments.
> >>
> >> FYI: 
> >> 
> http://sites.google.com/a/chromium.org/dev/spdy/An_Argument_For_Chang
> >> ing_TCP_Slow_Start.pdf
> >>
> >> This topic seems to be gaining momentum, and the WG should 
> take some 
> >> time considering if there is work here for it.
> >>
> >> Lars_______________________________________________
> >> tcpm mailing list
> >> tcpm@ietf.org
> >> https://www.ietf.org/mailman/listinfo/tcpm
> >
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