DSL Equipment

With the fundamental technology now covered all that is left is to now look at the equipment required to utilise an xDSL connection. In essence there are only two main pieces of hardware required and these are the DSL transceiver and the DSL Access Multiplexer (DSLAM).

The DSL transceiver is basically the equipment that is used to connect your computer to the DSL line. In the case of home users this will be the modem that is connected to your computer using either usb or an ethernet adaptor however business users may have the DSL transceiver technology built into a switch or router that is a part of their company network.

The DSLAM is a piece of equipment at the central office. It takes all of the individual xDSL connections from the region and combines them into one high capacity link to the Internet. The DSLAM is a flexible piece of equipment and can combine both CAP and DMT based DSL lines. One great feature that xDSL has over cable modem technology is that cable modems operate using a shared bandwidth conneciton meaning as more users are added the performance of existing users can drop slightly. xDSL works differently and each customer has their own direct connection to the DSLAM and therefore adding extra users will not impede performance, unless of course the number of users connected to the DSLAM gets so great that its high capacity connection to the Internet become saturated. In which case it is simply a task of increasing the bandwidth on the DSLAM to resolve the problem.

So why can't everybody have xDSL?

As mentioned in the introduction there are contributing factors that decide who is able to use xDSL. The biggest and most important of these is the distance you are from your service providers central office. As we know a signal travelling down a wire is subject to the resistance of the wires themselves and elso external interference, the result is that the signal gets progressively weaker the further it travels. For the xDSL service to be effective the distance from the CO to your home or business is limited to 5,460m (18,000 feet), however to provide speed and reliability most service providers limit this further as customers nearing the distance limits will experience very slow speeds. In theory xDSL is capable of a maximum download speed of 8 megabits/second and an upload speed of 640kilobits/second, however this is at a maximum distance of 1,820m (6,000 feet) from the CO. In the real world however the best speeds offered at the moment are 1.5megabits/second downstream and between 64 and 640kilobits/second upstream. You may however be wondering why standard calls aren't affected by this problem of distance and this is due to the use of amplifiers that boost your call as it travels long distances. These amplifiers however are not compatible with the signals used in xDSL and if an amplifier exists between your home or business and the CO then you will be unable to use the xDSL service. Also telephone lines that use fibre optics are incompatible with xDSL as the signals cannot be correctly converted between the transmission types.