Summary: Upload and download speeds quoted by your ISP aren't as directly related as you might imagine. It's easier to think of them as two separate things.
ISP connections seem to be rated in download/upload speeds, with download speeds being substantially higher. I'm often urged by my ISP to upgrade my service to a more expensive option that provides higher download speeds. What no one can explain is, how much faster can my download speed be if the servers I visit are limited to the slower upload speed?
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There's a bit of a misconception built into the question that I want to try to clear up.
Upload and download speeds aren't related. Well, technically I suppose they are, kinda, but for all practical purposes you should think of them as completely unrelated.
So the fact that a much faster download speed is available actually has nothing to do with the fact that your upload speed is much slower in comparison.
I know, it's confusing.
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The best analogy I can come up with is your car. You can travel forward much faster than you can travel in reverse. I'm not just talking about your skills as a driver, though I suppose that counts, I mean that your car is simply incapable of going as fast backwards as it is forwards. Your transmission, among other things, is simply geared that way.
And you probably don't care.
Why?
Because you spend much more time driving forward. It's how you get places. It's much more important to you that you move forward quickly than it is you be able to backup at a breakneck speed.
Could a car be built that could go the same speed in both directions? Of course. But by focusing on one direction, by optimizing for forward motion, your car is more efficient at it.
The same is true of your internet connection.
You download much more than you upload.
A typical web browsing session might involve several small requests sent from your computer to remote sites requesting pages (anything sent from your computer to the internet is an "upload", including requests to fetch pages), but the size of the pages and what they contain typically dwarfs the size of the original request by factors of 100 or even 1000 or more at times. A tiny 200 byte request for a YouTube video being uploaded could result in a download of many millions of bytes.
It won't matter to you that the upload of that tiny request is somewhat slower as long as that huge download is as fast as it can possibly be.
The designers of the various technologies that we use to connect to the internet have realized this, and use it to "shift the balance" in your connection. Whereas in the past you might have seen 50/50 allocation in your bandwidth - half for uploading and half for downloading - the technologies being implemented in many cases effectively take away some of the uploading capacity in order to make the downloading speeds faster. Perhaps an 80/20 allocation of the available capacity instead: downloads are faster because you do them more, uploads are slower but you're likely not to notice or care.
[I have to insert a note here to the pedants: yes, I know that I'm technically not exactly correct with this allocation metaphor, but it actually explains the concept very well. The fact is that technology, capacity, bandwidth and infrastructure are shifted in various ways from one direction to the other in order to provide a better user experience. The nitty gritty techie details are well beyond the scope of this article, or the needs of most of the people reading it.]
Not all technologies are "asymmetrical" - having different up and down speeds. Many dialup modems are (or were) symmetrical - having the same up and down speeds. DSL, more correctly ADSL for "Asymmetrical Digital Subscriber Line" was one of the first popular broadband connections to use this approach, and many others have followed in various ways. Other technologies remain symmetrical - connections between internet servers, for example, are very much like your own home LAN - the same speed in all directions. Some types of broadband, including connections such as the T-1 I use, are symmetrical by design as well. (I believe cable internet is asymmetrical, but I could be wrong. Most consumer and small business grade fiber, satellite and cellular broadband are all typically asymmetrical.)
Ultimately, unless you do a lot of uploading - running peer-to-peer software, uploading videos or the like - focus on the download speed. That's what really impacts your internet experience the most, by far.
Related:
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Do I need a new computer to keep up with my faster internet connection? If your new faster internet connection doesn't perform as expected there are several things to look at, but the age of your machine probably isn't one.
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What's a T1 line, and how do I connect to it? T1 lines are among the oldest of data technologies in use. They're fast, reliable and a tad expensive. We'll look at how they compare to alternatives.
Article C3766 - June 19, 2009
I could be wrong here, but I think you misinterpreted the OP's question.
I think what the OP wanted to know is this: let's assume your download speeds are 12 Mbps and your upload speeds are 2 Mbps. Why would someone purchase a more expensive plan that gives them faster download speeds if the server they're downloading from still is limited to an upload of 2 Mbps?
20-Jun-2009
Mike -- The upload /download speed of your service has no bearing on the upload speed of your end server.
you are in effect correct though that a 12 Mbps connection against a server capable of only uploading 2Mbps is just as effective as a 20 Mbps on your side against the same server /site.
The biggest reason to upgrade service is for multitasking as the majority of servers are limited in their upload speeds.
--zig
Posted by: Ziggie at June 20, 2009 3:25 PMI believe DAF made a car that could go as fast backwards as forwards (it used rubber belts so it had the same no of fwd/reverse gears), and the Austin Allegro had better aerodynamics backward than forward. Of course, Italian tanks go faster backwards than forwards ;-)
Posted by: JH at June 23, 2009 8:33 AMWhere the upload speed hurts the most is using a video web cam.
Posted by: Harry at June 23, 2009 10:42 AMDownload and upload are somehow related based on my knowledge reading over the internet. if your upload is high, your download speed slows. Server capacity is not really a problem if you want a faster download. All you have to do is to make sure that the seeder and leecher are almost the same like 50/50. There are some downloader that you have choices if you want to upload file while you are downloading it or not.
Posted by: x0x at June 23, 2009 6:30 PMAs Mike points out, the question seems to be one of "how is the remote server's upload speed affecting my download speed" and "if the remote server is bandwidth limited for its upload, doesn't that limit my download". The answer is that the remote server is likely not connected to "the internet" via the same bandwidth limited connect as your client machine is. Most servers are sitting on high bandwidth connections to the internet, often far in excess of 100Mb. Their connection speeds (up and down) are completely unrelated to your connection speeds. The net bandwidth that you have to any one server will be affected by factors which include: the server's bandwidth, the client's bandwidth, the load in all of "the pipes & switches" between the two, and even things like the distance between the two and how well tuned the software is on each of the two... its a complex equation.
One unmentioned large reason for asymetric bandwidth for many client's connections is... well... to prevent them from becoming effective servers. Your ISP can control via such knobs how much data you put on the net, and thus their costs. Likewise, the can employ technologies such as "caching proxies" to provide the client with an copy of a commonly fetched web page without even visiting the server (or just asking the server to validate the proxie's cache with a low cost transaction really ;-). Taken to the extreme, this is (in essense) the whole idea behind technologies such as Akamai's (a whole business built on this ;-).
Posted by: Nicholas Gimbrone at June 23, 2009 7:37 PM