Re: 50Mb across the country in 6 seconds

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
>>>
>>>
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>>
>> --
>> 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
Blogs and organic groups at http://www.ccie.net