What is DSL (Digital Subscriber Line)?

DSL (Digital Subscriber Line) is a family of communication technologies that are used to transmit digital data over telephone lines.

DSL uses higher frequency bands to transmit digital data, so that the same phone line can be used for Internet access and analog phone calls simultaneously. But on the customer premises, a DSL filter is needed to block any high-frequency interference going to the phone set.

ADSL (Asymmetric Digital Subscriber Line) is the most commonly used DSL technology by phone companies to provide Internet access over telephone lines.

The download speed of ADSL is higher than upload speed. This is why it is called Asymmetric DSL. Here is a comparison download and upload speeds of typical ADSL services:

Download: 
   Low    1.0 Mbps   16.7 min. to download a 10-minute video (125MB)
   Hight  7.0 Mbps    2.4 min. to download a 10-minute video (125MB)

Upload:
   Low    0.4 Mbps    1.7 min. to upload a photo (5MB)
   High   1.0 Mbps    0.7 min. to upload a photo (5MB)