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Upload Causes download to suffer

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  • 22-02-2008 3:11pm
    #1
    arseagon
    Registered Users Posts: 598 ✭✭✭


    I have a 6Meg download on DSL with a 512K upload. Recently I've noticed that if my server is sending out lots of large e-mails, It sends them as quickly as it can and ramps the upload up to max. Now while these mails are sending, the general surfing speeds of the system slow to a crawl. Has anyone else ever seen this or know why it would be happening?

    I have the option of band limiting the servers IP address but I want to know if there's any other way to deal with it?


Comments

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    #2
    h57xiucj2z946q
    Closed Accounts Posts: 2,267 ✭✭✭h57xiucj2z946q


    thats normal due to packet verification.


  • Options
    #3
    Peanut
    Registered Users Posts: 1,462 ✭✭✭Peanut


    If the server is a linux box, there was a short script called wondershaper which you could use to reserve a small amount of upload bandwidth for the ACK packets that need to be sent to have fast downloads.

    There're probably better options now, but the above script was simple and effective. Here's the page for it.


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    #4
    jimmycrackcorm
    Registered Users Posts: 14,339 ✭✭✭✭jimmycrackcorm


    This speed problem is the same with torrents, if you unrestrict your uploads then your download suffers.


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    #5
    Snaga
    Registered Users Posts: 1,562 ✭✭✭Snaga


    When transferring large files most applications use TCP to make sure the files are sent reliably (Yup - thats the TCP in TCP/IP). This involves a series of acknowledgements from your PC to say that you have received the data.

    So if you are maxed out on your upload due to your email going out and you start downloading a file seperately, the file server will send you a small bit of data (which gets through just fine as your download BW is not being used) it will then wait for your PC to acknowledge that it has received them before sending any more.

    This acknowledment has to fight its way back out to the file server through your congested upload (with all of that email data) and is often lost due to the congestion - meaning the server sending you the file sends the previous data again as it does not receive the expected acknowledgement. As you can imagine this means it takes a whole lot longer to receive the file than normal.

    This is why online speedtests are not in any way accurate while your torrents are maxing out your upload!! ;)


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