calculating download speed

Unanswered Question

There are lot of online tools that help measure the ideal time it should take for a particular size file to get downloaded based on the link speed. But these generally does not factor the latency if it exists between the source and the destination


for eg.. is there a way to calculate the time required for downloading a 128MB file over a 1Mb link when the latency is 300ms under ideal conditions?


Ambi

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rajivrajan1 Mon, 08/04/2008 - 21:35
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is this a internet link ?


Do u want to chk the speed of internet


or any point to point?


if internet which destination and what is the speed of that destination ?


johnakeating Mon, 08/04/2008 - 21:43
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Packets are sent on the assumption that it will make it to the other side. So the latency in between the computer is not really going to affect the over all speed(it will just not much).

Joseph W. Doherty Tue, 08/05/2008 - 03:06
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Is there a way to calculate the time for a download? I'm sure there is, but haven't seen a tool that does so.


Latency has a couple of major impacts to bulk data transfer performance. Assuming you have in mind TCP, latency impacts how fast TCP ramps up during its "slow start" phase. The second major impact of latency, it's one of the factors of BDP (bandwidth delay product). If the receiving host's TCP receive window isn't big enough to support the BDP, TCP will not ramp up to full link speed. There are tools that will calculate BDP.


Aother factor that might impact bulk transfer performance, is the ratio of overhead to payload. If you have a large MTU, the percentage loss to overhead is usually minor, but if the MTU is minimal size, the payload tranfer rate, as might be measured by a download, might be noticeably slower than the media line rate.

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