Digital Subscriber Line (DSL) is a communication medium that is used to transmit digital data over telephone lines. DSL is a popular technology used by call center outsourcing industry. DSL is sometimes referred to as a last-mile technology because it is used only for connecting a telephone switching station to a home or office and not between switching stations. DSL is typically used by telephone companies to offer data, video, and voice services over these existing copper telephone lines. DSL services can be delivered simultaneously with wired telephone service on a single telephone line. DSL service is always on, you need not dial your ISP for this. The primary feature of DSL does not disrupt the operation and quality of existing analog telephone service.