What is DSL broadband connection?

DSL stands for {Digital Subscriber Line} and is a fast growing technology that uses a normal phone line to provide high-speed broadband  internet access for home and small office. The DSL signal is carried 

Figure 1.0 widely used modem in Ethiopia

by two modems - one in your premises and one at your local telephone exchange(local ETC office). These modems are designed to exploit the physical transmission capabilities of the copper wires to deliver higher data transfer rates. Your existing phone master socket is modified to split the line into two channels (using a central line splitter), so that one line is used for normal voice transmissions (ie. telephone) and the other for your DSL internet access, except i don't see ETC implement this method, instead what ETC does is they dedicate one line for the DSL connection.
The bit rate of consumer DSL services typically ranges from 256 kbit/s to 40 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and service-level implementation

There are two types of DSL available:
ADSL - Asymmetric Digital Subscriber Line, which typically provides a faster downstream data flow, 5Mbpx for download,  and a lower upstream speed 1Mbs to upload (making it ideal for users who do more downloading than uploading); and its what most of us use at the internet cafe' or small offices, here in Ethiopia. 
and 
SDSL- Symmetric Digital Subscribe Line, provide equal bandwidth for both uploads and downloads. Symmetric DSL technology is popular for business-class DSL services as companies often have greater needs for transferring data. Typical symmetric DSL connections support 1.5 Mbps for downloads and uploads.