Internet drastically slows down when uploading at the same time

Discussion in 'iMac' started by fuchsi, Sep 2, 2010.

  1. fuchsi macrumors member

    Aug 26, 2010
    Has anyone encountered this problem?

    I'm uploading a clip onto Vimeo and while it's working i'm surfing the net.
    Thing is it's suddenly very slooow.
    Was the same yesterday when i was uploading to rapidshare that the internet connection suddenly dropped!

    Any suggestions?

  2. miles01110 macrumors Core


    Jul 24, 2006
    The Ivory Tower (I'm not coming down)
    What kind of connection do you have? You should probably get a faster one.
  3. bukalemun macrumors member

    Jul 21, 2010
    When you surf on the internet, you make DNS requests, connect to the sites you are about to visit, etc. These are all small uploads to the sites. And when you download something from those sites be it a picture or a page, you always send an acknowledgment packet for every data packet they send to you.

    When you upload and surf at the same time, if you are uploading with all bandwidth available to you, your computer may not be able to send these aforementioned packets fast enough and so your download speed drops down.
  4. fuchsi thread starter macrumors member

    Aug 26, 2010
    Thanks bukalemun, that sounds like a proper explenation.
    I was just wondering cause compared with my old Hp laptop it seemed kinda slow.
    I remember doing the exact same thing and the connection would still be very fast.
    Maybe it already had all the cookies from the sites i was visiting hence the fast connection.

    Thanks anyways
  5. bukalemun macrumors member

    Jul 21, 2010
    Yeah, the browser cache may be playing a role in speeding things up. Anyway, limiting the upload speed will really help. 5% free upload bandwidth will mostly be enough for fast browsing if you are using broadband speeds.
  6. tears2040 macrumors 6502

    Aug 27, 2010
    How do you limit this on Safari?

  7. fuchsi thread starter macrumors member

    Aug 26, 2010
    yeah i can't find it either (i'm on firefox)
    Maybe some help...i looked around but couldn't figure it out

  8. aliensporebomb macrumors 68000


    Jun 19, 2005
    Minneapolis, MN, USA, Urth

    First go to and report your findings back as to your internet connection.

    In the United States and most other locales, the download speed will be your highest number and the upload speed will be a small fraction of that.

    That's the problem but to get "faster" you need to pay your internet service provider more for a better connection.

    Anyway, report back and I can make some informed observations.
  9. Mars2010 macrumors member

    Aug 19, 2010

    Thanks for the explanation, too. I was wondering why my kids complained about their connection on the PS3 as I was surfing on the iMac. They don't seem to think the connection is as bad when the PC is in use instead. That can't be's the same internet connection, afterall...
  10. uberamd macrumors 68030


    May 26, 2009
    TCP requests use both download and upload bandwidth. For example, when transferring data on my local 1Gbps LAN from my laptop to my server, my connection speed on my laptop often looks like this:

    30MBps Out, 350KBps in

    While my laptop is primarily sending data out, it is still receiving a lot of data. Why?

    The reason is that TCP, unlike UDP, verifies with the sender that the packets were properly received. So while downloading over TCP, you are also uploading the response saying "I received the packets, send me the next batch". Since the upload pipe is very narrow compared to the download pipe, downloads and uploads at the same time cause the download TCP reply to fight with the data you are uploading for that limited pipe, and thus slow everything down.

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