Tests: Download vs. Upload
The differences between our Download and Upload tests aren’t as obvious as they may initially seem. Yes, the basic difference is the direction of the data transfer: Simply put, the Download test measures your connection speed for viewing Web pages; the upload test measures the speed for maintaining them–or sending data over your connection.
However, the rated upload and download speeds may not be the same for your connection. Some connections, such as 33K and lower, are “symmetric,” meaning the rated upload and download times should be the same. Other connections, such as cable modems and ADSL, are “asymmetric” (the “A” in ADSL stands for asymmetric). This means the upload and download times won’t necessarily be the same; upload times are generally not as fast as download times. For instance, the rated speeds for ADSL are 1.4Mbps down, and 400Kbps up. Cable modems are typically rated at 1.5 to 3Mbps down, and 400 to 600Kbps up.
Occasionally, you may even see opposite results, especially on cable modems during the evening hours. If your connection has a heavy user load, the download times may suffer, while the upload times remain unchanged. This is because the majority of Internet users download data instead of uploading it.
In addition, the ways we actually conduct the tests aren’t quite comparable. Our Download test uses the http protocol and grabs one big stream of data. Our upload test uses the ftp protocol, which involves a lot of handshaking across Internet servers. As a result, the test is more susceptible to interruptions because of bad ping times on a server or servers.
Bottom line: You should regularly run both tests to make sure you’re getting the rated upload and download speeds from your connection.
