overview - dsl

DSL

DSL stands for Digital Subscriber Lines. Most people know of it as a means of getting high-speed Internet access to their homes. The same technology that brings high-speed Internet to your home may also be used within a property. DSL solutions are more costly due to the increased complexity of the solution and the requirements for equipment at the connection point in the room.

DSL solutions should be considered where the use of the lower cost Ethernet network cannot be supported by the property's infrastructure, where the costs of rewiring are too high, or the owner cannot justify the expense. Another advantage is it's distance capabilities. DSL can provide network connectivity over very long distances, which makes it a good solution for connecting buildings that are several hundred feet apart.

There are two specific classifications of DSL: asymmetric (meaning different upload and download speeds) and symmetric (meaning the same speed both ways). The short answer for commercial applications is to use only symmetric DSL.

There are many types of DSL, but the more common classifications of DSL networks are:

HomePNA: speeds up to 1Mb/sec up to 350 feet
SDSL: speeds up to 1.5Mb/sec at distances up to 15,000 feet
HDSL: speeds up to 2.3Mb/sec at distances up to 20,000 feet
VDSL: speeds up to 56Mb/sec at distances up to 4,500 feet

There are two distinct features that identify a DSL solution: the use of a single pair of wire and the use of a DSL concentrator and DSL endpoint to make the network connection. Here's how DSL works: all network cards require Ethernet as the means for connecting two computers. Ethernet requires four wires. Since DSL uses two wires, one must convert the four-wire signal to a two-wire signal and then back again. That is what the DSL concentrator (known as a DSLAM) does. DSL can carry voice and data traffic over the same pair of wire at the same time because data is transmitted at a different frequency than the telephone uses. Think of it as a divided highway and you'll get the idea.

To convert the two-wire signal back to a four-wire signal, a device commonly called a DSL modem, must be used. It is this device that the computer connects to with a standard Ethernet cable. Conversely, it too converts the Ethernet signal to a DSL signal, which is then reconverted in the DSLAM for transmission onto the Internet. To make the point differently, it is possible to use two DSL modems to connect two computers, although it is not practical.

DSL comes in many different types. The more common are HPNA, sDSL, and vDSL. Speeds vary and you should take those speeds into account when considering DSL as a solution as higher speeds increase costs.