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Premium cable Internet is supposed to provide multi-megabyte per second downloads, right? Meaning, I should be able to download a 20MB file in a second? When I download large video files, say from YouTube or some HD video sites, and I watch the download speeds on my Google Chrome download page, it always ranges between 200kbps and 900kbps. Usually, a download will start at 700kbps, but after a few seconds it slowly drops and drops then stabilizes between 200 and 400kbps on average.

Why don't I ever download anything even close to the speed I am supposedly paying for?

Is it perhaps that I am using a 4 year old Motorola Surfboard cable modem, and a 4 year old Linksys Wireless-G router? Is my hardware holding me back, or is this as good as it gets?

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3 Answers 3

The key thing here is what appears to be a mixup between MBps (megabytes per second) and Mbps (megabits per second)

A byte = 8 bits, so if your connection is like mine (15 Mbps), then your maximum speed should be around 1.875 MBps (15 divided by 8).

I have yet to hear of anything reaching close to 20MBps for a home connection in North America that isn't hundreds of dollars a month.

On top of all of that math, those speeds are "up to". No carrier guarantees speeds. I only ever hit a max of about 1.4 MBps. You also have to factor in overhead, latency, and a ton of other factors.

Additionally, some traffic is shaped, meaning that it's speed is changed. Some carriers will lower your BitTorrent speed because it hogs bandwidth.

Lastly, some web servers don't upload at the speed you're looking for. They might only upload at 200kbps, which means that that's the speed you're gonna get. No way around this point...

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The speed of a download is limited by the narrowest link in the chain. For example, if Youtube won't serve more than 200kB/s (sure, they have a very big pipe, but you've got to divide by the number of users), that's what you get, even if your local link can accomodate more. If the website is the limiting factor, you can download from several sites in parallel while benefiting from the maximum bandwidth for each.

Just because your ISP sells you an “up to 20MB/s” connection doesn't mean they actually provision that much bandwidth for you. There are several reasons why you may not reach the advertised maximum. There may be technical limitations; for example, with DSL, the further you are from from the telecom company's equipment, the smaller the maximum technically achievable bandwidth gets. With cable, bandwidth is often shared over a whole building or block. And if the ISP advertises an “up to X” bandwidth (they usually do), they're complying with their contract if they provide less. If your ISP's effective bandwidth is not enough for your tastes, your only recourse is to find a better ISP.

(Guaranteed bandwidth contracts do exist, but they're a lot more expensive. Medium-to-large businesses often have contracts with something like X guaranteed all the time, 100*X maximum, and 10*X available 95% of the time.)

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When I first got high speed access many sites on server data at 56kbs (high speed modem rates). However, I could browse multiple sites at the same time without slowing down any site. We now expect, and usually get much faster response.

Due to windowing it is unusual to get the full speed out of any high speed connection. Network round trip times have an inverse relation to throughput. All things being equal the close a site is the faster it will be. Increasing the window size may increase the download speed, but there are window size limits.

Network routing can greatly increase the network distance to a site. Usually I access sites in north-east USA via a fairly direct route that goes 100 miles north-east to Montreal then south to the site. Other times the route from Montreal goes to the west coast along the way. This significantly slows the transfers. Fortunately, most of these slow downs are not overly visible when viewing a web site. File transfer speeds are much slower with this routing.

That being said, if you only transfer one file at a time you will have unused (wasted?) bandwidth. You may find that you can download two or more files at the same time without a significant decrease in download speed. As you add more connections, the speed will begin to slow down as you begin to fully utilize the available bandwidth.

Having a high speed connection reduces the connection latency at your end. This will marginally increase your transfer speed. Google.com has a latency of 25ms for me, while another site has a latency of 90ms. All things being equal, I would expect better file transfer speeds from Google.

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