DSL, originally called digital subscriber loop, is a technology using a high speed transmission over twisted-pair copper wires used in traditional telephone lines. It was designed to transmit data faster than a standard modem using dial-up services, while using the same wiring. The data is carried on different frequencies than a conversation, allowing a single line to be used for both data and voice concurrently.
There are many variations of DSL technology. How it is implemented changes depending on carrier and country. And each variation has its own equipment as well. Some of the different types of DSL are ADSL, SDSL, RADSL, VDSL, HDSL. In the UK, ADSL is the primary type of DSL installed in most homes.
On the consumer end, installation requires a filter to separate the data signal from the voice. The filter blocks frequencies above 4 KHz to prevent the DSL data streams from interfering with the normal voice communications of the telephone line (the human voice frequency doesn’t go above 4 KHz). In addition, a DSL modem is connected to the computer to interface the data requests from the user to the telephone line, then to the service provider’s location where it is combined into one larger data stream on a high bandwidth connection.
The upload and download rates experienced by consumers vary depending on the distance from the closest telephone exchange. This is one of the downsides to DSL. Studies performed on ADSL lines in 2011 indicated that actual upload and download speeds were significantly less than advertised. Service providers in the UK are now required to inform consumers of actual rates they will experience at their location before contracts are signed. DSL has improved since it was first introduced however, as carriers have run more lines and installed repeaters. Download speeds can be up to 40Mbps close to exchanges, but often speeds are more around 15Mbps. Streaming movies isn’t an issue at these speeds, but upload speeds might not be sufficient to originate a stream.
Anyone planning on using a DSL connection to upload a stream, particularly a live webcast, should check with their service provider to find out what the actual upload rates are. It is also possible to test current speeds by visiting various sites on the Internet that offer testing services like speedtest.net.