Re: 50Mb across the country in 6 seconds

Bandwidth does affect throughput, including that of TCP. The Bandwidth
Delay Product gives you maximum theoretical amount of data that you can
have in flight on a circuit. For a TCP session that becomes the
theoretical maximum amount of unacknowledged data which you can send whilst
awaiting the next ACK. This is theoretical, as it does not take into
account protocol overhead.

To sustain that maximum throughput with TCP you need to have windows (and
buffer) of at least the BDP. To support a really big window, you need to
use window scaling. If your window is too small, you will have periods
where you are waiting for an ACK, with your TX idle, before you slide the
window along and can then continue sending additional segments. I presume
window scaling limitations was what Joe was alluding to.

MTU also does matter with bulk data transfer, though it is often less
important than the window size. If you have a smaller MTU you need to
send more packets. If you send more packets you use more overhead, so your
communications is less efficient and takes a little longer.

There are a multitude of different versions of TCP available designed to
overcome some of the performance problems of the original protocol.
 Despite that, if you want really fast IP transmission, and don't need
reliability, UDP is your man.

Paul.

On Sun, Mar 4, 2012 at 8:34 PM, Paul Negron <negron.paul_at_gmail.com> wrote:

> Note****The original problem was not specifically stated as being TCP
> based.
> (Just getting that out of the way)
>
> You and Carlos are agreeing but talking right past each other.
>
> This is what he said to your point:
> " If the control protocol is TCP or TCP based, window size makes impossible
> to keep sending data at link speed and your performance gets capped"
>
> He tends to set people off with a disagreeable statement first before
> making
> a point (I don't think he means any harm). I have learned this through
> time.
> Regardless, he said what you said from a different perspective ( a little
> more wordy perhaps but accurate).
>
> Paul
> --
> Paul Negron
> CCIE# 14856 CCSI# 22752
> Senior Technical Instructor
>
>
>
> > From: Joe Astorino <joeastorino1982_at_gmail.com>
> > Reply-To: Joe Astorino <joeastorino1982_at_gmail.com>
> > Date: Sun, 4 Mar 2012 15:09:54 -0500
> > To: Carlos G Mendioroz <tron_at_huapi.ba.ar>
> > Cc: Jersey Guy <guy.jersey_at_gmail.com>, Cisco certification
> > <ccielab_at_groupstudy.com>
> > Subject: Re: 50Mb across the country in 6 seconds
> >
> > When you are calculating maximum theoretical throughput with TCP,
> > which is what I was explaining it doesn't. It doesn't matter if you
> > have a 1Mbps or a 10Gbps link, the calculations for theoretical
> > maximum THROUGHPUT will be the same. Look it up. If you have enough
> > bandwidth to actually push the theoretical maximum throughput that is
> > great, but the bandwidth is not part of the equation.
> >
> > On Sun, Mar 4, 2012 at 6:35 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar>
> wrote:
> >> Joe, you make it sound like link speed does not make it into the
> equation,
> >> when it obviously does.
> >>
> >> The magnitude that usually is important in making good use of a link
> >> capabilities is BDP, Bandwidth Delay Product. As links get faster,
> >> and latencies go up, the BDP of a link grows above what the control
> >> protocol is able to use, and then you are unable to really use
> >> all of your link capacity.
> >>
> >> If the control protocol is TCP or TCP based, window size makes
> impossible to
> >> keep sending data at link speed and your performance
> >> gets capped. But that is a control protocol defect, and hence can
> >> be relieved by using, e.g, WAAS. (or paralelizing with many streams,
> >> or...)
> >>
> >> Bottom line: I believe that 50 MB xfer in 6 seconds is doable.
> >> And, more important to the 1st message, MTU has little to do with it.
> >>
> >> -Carlos
> >>
> >>
> >> Joe Astorino @ 03/03/2012 21:00 -0300 dixit:
> >>
> >>> Sorry I meant RTT and window size not MSS. TCP throughput in bits per
> >>> second can be calculated as window size in bits / RTT in milliseconds
> >>>
> >>> You always have to take latency into the equation and it makes a huge
> >>> difference as latency goes up. TCP window scaling can help
> >>> dramatically but make sure you do not have unrealistic expectations.
> >>> Maximum theoretical tcp throughput as you see here is a function of
> >>> RTT and window size not link speed.
> >>>
> >>>
> >>>
> >>> On 3/3/12, Joe Astorino<joeastorino1982_at_gmail.com> wrote:
> >>>>
> >>>> You can't forget to take into account the L4 transport mechanism. TCP
> >>>> will obviously have some impact on the speed because of the
> >>>> acknowlegement nature of the protocol.
> >>>>
> >>>> Ultimately your throughput calculation will have to consider RTT and
> >>>> MSS if you are dealing with TCP
> >>>>
> >>>>
> >>>>
> >>>> On 3/3/12, Jersey Guy<guy.jersey_at_gmail.com> wrote:
> >>>>>
> >>>>> Hello Gents. This DBA guy tells me he copied a 50Mb file from his
> >>>>> machine
> >>>>> in New Jersey to a server in California in 6 seconds. I told him
> that's
> >>>>> not
> >>>>> possible because the smallest link in the path is 1Gb/sec but MTU is
> >>>>> 1500,
> >>>>> so even if you take wire speed, it would be at least 33 seconds
> before
> >>>>> the
> >>>>> file was copied. Am I wrong in saying so?
> >>>>>
> >>>>> TIA
> >>>>>
> >>>>>
> >>>>> Blogs and organic groups at http://www.ccie.net
> >>>>>
> >>>>>
> _______________________________________________________________________
> >>>>> Subscription information may be found at:
> >>>>> http://www.groupstudy.com/list/CCIELab.html
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>
> >>>> --
> >>>> Sent from my mobile device
> >>>>
> >>>> Regards,
> >>>>
> >>>> Joe Astorino
> >>>> CCIE #24347
> >>>> http://astorinonetworks.com
> >>>>
> >>>> "He not busy being born is busy dying" - Dylan
> >>>>
> >>>
> >>
> >> --
> >> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
> >
> >
> >
> > --
> > Regards,
> >
> > Joe Astorino
> > CCIE #24347
> > http://astorinonetworks.com
> >
> > "He not busy being born is busy dying" - Dylan
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
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Received on Tue Mar 06 2012 - 23:43:08 ART