Is distance a problem for DSL internet?

Written By: Sonal Gurjar

DSL is one of the cheapest forms of high speed internet. But, yes, distance is a problem for DSL since it is distance sensitive. DSL, or Digital Subscriber Line, provides high speed, secured data connection over dedicated telephone lines. As the connection length from the telephone central office increases, signal quality and connection speed starts deteriorating. It is not the straight line distance from your home that matters; rather it is the length of wire between your house and their central office. The copper wire running from the central office to the telephone jack is known as the “local loop.”

Voice signal ranges from 400 Hz to 4,000 Hz. Thus, telephone cable was not created to be exactly compatible to pass high frequency signals. With the subsequent development of DSL technology, data was sent alongside the voice signal on twisted wire pair. DSL uses frequencies higher than 1 MHz, and there is a limit to which high frequency data can travel because of the vulnerability to signal loss. The reason behind this is copper metal has an impedance consisting of distributed resistance, capacitance and inductance. This impedance depends upon the length of the local loop, and the type and thickness of the wire. In a regular analog, voice signal degradation is not very critical and telephone companies use amplifiers called loading coils to boost voice signals. These loading coils could not be used with DSL signals. Moreover, digital data packets need to be sent precisely, without any signal loss or interference. The copper wire used for a local loop may be of varying thickness ove
r its path, and that too affects signal strength. This is because attenuation (loss of signal strength over distance) is greater with thin wires.

In a nutshell, places that are closer to the main office get high speed service and more bandwidth, but as one moves away, this starts degrading. For example, at a maximum of 6,000 feet from the CO, speed is 3 Mbps, but as the limit increases, speed and quality have to be traded off. The effective range of ADSL is between 15,000 feet and 18,000 feet from the central office, depending upon copper wire thickness. As the length of the twisted wire pair increases, DSL bandwidth decreases for both uploads and downloads. ADSL claims to provide a  maximum speed up to 8Mbps downstream at 6,000 feet and upstream speed up to 640Kbps. 

If your area is served by fiber optics, then distance is not a problem. Fiber optics overcome the limitations of metal wire because there is no resistance. It carries an all-digital signal and there is no interference from magnetic or electric fields. When you contact your internet service provider for a DSL connection, they will check distance from the CO if your area does not have fiber optics. Thus, when making a decision between DSL and other services, determine how far you are from a DSL hub. Otherwise, you have to compensate that with low speed. If you are further than the maximum limit, DSL might not be available. One can use online DSL lookup service to check whether DSL is available at a particular place or not.