Equipment
The customer end of the connection consists of a Terminal Adaptor or in layman’s terms “DSL modem.” This converts data from the digital signals used by computers into a voltage signal of a suitable frequency range which is then applied to the phone line.
In some DSL variations (for example, HDSL), the terminal adapter is directly connected to the computer via a serial interface, using protocols such as RS-232 or V.35. In other cases (particularly ADSL), it’s common for the customer equipment to be integrated with higher level functionality, such as routing, firewalling, or other application-specific hardware and software. In this case, the entire equipment is usually referred to as a DSL router or DSL gateway.
Some kinds of DSL technology require installation of appropriate filters to separate, or “split”, the DSL signal from the low frequency voice signal. The separation can be done either at the demarcation point, or can be done with filters installed at the telephone outlets inside the customer premises. Either way has its practical and economical limitations. See ADSL for more information about this.
At the exchange, a digital subscriber line access multiplexer (DSLAM) terminates the DSL circuits and aggregates them, where they are handed off onto other networking transports. In the case of ADSL, the voice component is also separated at this step, either by a filter integrated in the DSLAM or by a specialized filtering equipment installed before it. The DSLAM terminates all connections and recovers the original digital information.