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In Internet terms, “downstream” data travels from the Internet to your computer. Every time you visit a webpage, the contents of that page must be downloaded to your PC to view the material, just as this page was downloaded. High-speed Internet Service Providers (ISPs) price plans based on how fast data can be downloaded, as slow download speeds results in slow surfing. But you are also constantly uploading information, or transferring data “upstream” from your computer to the Internet.
An upload occurs every time a request is sent from your browser to the Internet; for example, when clicking on a link. The upload in this case is a small packet of data that includes your Internet Protocol (IP) address, the page you are requesting, and a few other bits of information. The data packet or request traverses the Internet to arrive at the server that contains the information or webpage requested. The return trip is the download.
Since requests for webpages contain very small amounts of data, ISPs conserve bandwidth by making the upload speed of a typical Internet connection far slower than the download speed. The download speed might be 1,500 kilobits per second (kbps) to accommodate receiving bulky Web pages, but the request for that page is only a few kilobytes that can be delivered lightening-fast at a throttled back 350kbps — the upstream rate.
You can picture this in terms of two tunnels, with the download tunnel being roughly four-times larger than the upstream tunnel. In most cases one won’t notice the slower upload speed, until you try to upload a large file. Why would you do that?
There are a number of situations online that call for uploading files. If you build a website, you’ll need to upload webpages and related content to the domain server, the computer hosting the website. Text-based files will upload quickly, but large images, music or multimedia files will take a bit longer. If you belong to a socializing site like FaceBook® or MySpace®, you might want to upload digital photos, MP3 or video clips to your profile. Maybe you’d like to make a movie of yourself performing an original tune and upload it to YouTube®.
Torrenting, a social networking architecture that allows users from all over the world to trade files between themselves, requires a 1:1 share ratio to avoid throttled download speeds. For every file downloaded, the user must upload a file of equal size. If a user isn’t aware that his or her Internet connection is much faster in one direction than the other, torrenting highlights the point. A user that spends three hours downloading a file, might have to leave the computer running 12 hours or more to upload the same amount of data.
Some businesses with non-local offices that are linked through the Internet using a Virtual Private Network (VPN) might require upload speeds that match download speeds. This would allow an employee in New York, for example, to upload a large file to an employee in Los Angeles in minutes, rather than hours. This is called a synchronous connection, whereas most plans are asynchronous. Synchronous ISP plans are more expensive than asynchronous plans, and therefore not as common.