Time Warner Cable - Legacy → [TWC] During upload, download basically stops working.

We have TWC in Queens, NY. Whenever we upload a file, download slows to a crawl, almost unsuable. And this is not torrents. Ex: uploading to youtube, simple small files etc.

TWC says this is completely normal because the upload is using all allotted bandwidth...

Any ideas? If this is not true, what should I tell them?

Yes it's true if you saturate your upload bandwidth, downloads will come to a crawl.

It's the way TCP/IP works. It's because the ACK (acknowledgment) packets telling the server you're downloading from you've properly received what it's sending can't get back to the server or are seriously slowed in response. They're waiting in line with what you are sending.

Routers and software QoS that prioritize ACK packets vs other upload traffic help. Otherwise don't saturate your upload bandwidth, leave 10% for other traffic to get through.

Here's an old but decent writeup on the subject:
»homepage.ntlworld.com/ro ··· nup.html

As DrDrew already explained it's normal with TCP/IP. Whenever you are downloading anything it needs to send back "ACK" (Acknowledge) to the sending server to let it know that it received the data in good condition.

Just for example - say the server sends you 1Kb packet your PC sends back an ACK for that, now you probably have a 15,000Kbps or higher connection so it has to send back tons of ACKs each for each of those packets.

Downloading at say 50Mbps, you'll need to send back about 1Mbps of ACKs or so (ok maybe that's pushing it - i'm just guessing here). So if your YouTube upload is using 4.5 of your 5Mbps upload then you can't ACK fast enough to download faster.

Using UDP now is another story but yeah we'll leave that alone for another day as hopefully that was already too confusing... LOL

That is why when my Grandmother uploaded her saves to SkyDrive it will cause audio streams to drop out. I wonder if there is anyway you can throttle a connection for only that computer?

Cool, thanks so much for all the information guys. I will look into QoS.

Final question just trying to rule something out here that it's something with TWC. At my other home, I have identical service but it's with Cablevision (optimum), same router, and when uploading, download slows but not nearly as much as it does with TWC.

If you are running Tomato firmware, go look at this thread. It has good information even if you don't run tomato.
»www.linksysinfo.org/inde ··· t-138585

Other good threads.
»www.linksysinfo.org/inde ··· n.31234/