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If I am uploading a file to a server on another network (with a different service provider), does the speed of upload depend on download speed of the server ? Is viceversa also true ? i.e if I am downloading a file from that server, does it depend upon its upload speed limit?

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For TCP it does (but not solely on (SRC, DST) but "men-in-middle" between them as well).

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Yes, the destination server's download speed will affect the source server's upload speed, and vice versa.

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Only with VERY extreme differentials - go read up on selective acknowledgements – symcbean Feb 11 '11 at 13:03
the OP didn't ask about any of that. He asked if the upload speed of one server affects the download speed of the other server. In a nutshell, it does. Of course there are other factors at play but he wasn't asking about any of that. Yes, I could have written a term paper on selective ACK's and pathMTU, and blah, blah, blah but none of that was called for in the answer to this very basic question. These downvotes kill me sometimes. I give a correct answer and get downvoted because I didn't tell the OP about the affect of solar flares on electronic transmissions. – joeqwerty Feb 11 '11 at 13:12

That's a rather confusing question but if I read to correctly you're asking if the download speed of B will affect an upload from A to B.

TCP communications are two way, so that while you are uploading the two systems have two-way background communications going on at a low level (ACK, NACK, that type of thing). While the bandwidth required for that background communication is quite insignificant, in an extreme case it may have a very minute impact, although it should never be so great that you would be able to notice it.

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Strictly speaking, the speed of the transfer is most affected by the speed of the slowest link in the path between the two systems.

So if the downloader system is on a 1Gb network, and the server is on a 100Mb network, and the site-to-site transit is a T1... then the T1 is the straw that most affects the upper limit on the transfer speed.

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