Cable companies are able to use the large amounts of data that travel through coaxial cables to deliver high-speed Internet connections. A cable modem is the device that sits in your home and receives the data signals that connect your computer to the Internet. Together, upstream and downstream comprise the total bandwidth or speed of your Internet service.
Broadband Internet access gives computers an always on, high-speed connection to the web as opposed to dial-up, which is extremely limited by comparison. There are several technologies that are capable of delivering high-speed Internet such as DSL, fiber optics, satellite and cable. Each of these technologies is capable of delivering different access speeds. For example, cable Internet is generally capable of up to 2 megabits per second (download) and 600 kilobits per second (upload).
Upstream or upload speed is the term given to the data that your computer sends out to the Internet. Your computer uploads data anytime you send an email or post a picture to Facebook or a server using FTP. Generally, the upstream speed capable via cable modems ranges from 400 kilobits per second to 600 kilobits per second (Kbps). This represents the total bandwidth of data your computer can send out to the Internet each second at full speed.
Downstream or download speed is the term given to the data that your computer receives from the Internet. Whenever you download music, pictures, webpages and other documents, you are using your computer's downstream bandwidth. Cable modems are typically rated at 1 to 2 megabits per second (Mbps). This means that you can download up to 2 megabits of data each second operating at full speed.
Upstream vs. Downstream
Cable modems have what is known as asymmetrical speeds because upstream and downstream capabilities are different. Your computer is capable of downloading data two to three times faster than it is capable of uploading the same data. As the majority of functions utilize your downstream bandwidth (web browsing, downloading music, watching videos), having a significantly slower upstream is a non-issue for most people. There are a variety of "bandwidth speed tests" available on the Internet that test and display the actual speed of your cable modem.