Introduction The telephone network is a ubiquitous and mature medium of communication with high levels of consumer penetration and potential data carrying capacity. DSL (Digital Subscriber Line) is one of the technologies used to provision high speed links to data networks over twisted pair Public Switched Telephone Networks (PSTN). These networks were originally designed to carry voice traffic over twisted pair copper lines (Jones, 2006). The Line in DSL refers to link between the consumer’s location and the local exchange. The PSTNs usually operate in the frequency range between 300Hz to 3.4 kHz of the total 1.1 kHz of spectrum available for voice communications. DSL usually provides high speed data communication by operating in the unused frequency range of the telephony spectrum above 3.4 kHz. DSL technologies support both bus and star topologies of network deployment and utilize pairs of compatible transceivers to facilitate communication between the consumer site and the telephone exchange (Littman, 2002). The transceivers usually installed at telephone exchanges or central offices must be able to separate the voice and data traffic, the voice traffic is usually sent over the PSTNs while the data traffic may be forwarded to high speed data networks. The telephone exchanges provide services to subscribers using DSLAMs (Digital Subscriber Line Access Multiplexer). In the upstream direction the DSLAM multiplexes traffic from multiple user ports carrying traffic of a single user to a few network ports carrying traffic for multiple users. In the downstream direction DSLAM de-multiplex traffic from network ports onto the correct user ports (Jones, 2006; Jayant, 2005; Golden, 2007; Maxwell, 1999; Smith, 2007). The range of DSL technologies is quite broad, but they can be roughly broken down into two types. Symmetric DSL In these types of technologies both the upstream and downstream links support the same data transfer rate. Asymmetric DSL In these types of technologies the data rates of upstream and downstream links are dissimilar. The above description is not complete since some technologies support both symmetric and asymmetric modes of communication and variable transfer rates (Jones, 2006). Transmission Technologies Before delving too deep into details of DSL technologies a review of transmission technologies deployed over voice networks is in order. The telephone voice data network, commonly referred to as Public Switched Telephone Network (PSTN) operated in the frequency ranges of 300 Hz to 3.4 kHz. Voice signals are primarily analog in nature; however advances in modern technologies have led to digitization of these analog signals to digital signals. Digitization of signals usually takes place in the main backbone networks connecting Company Offices (COs). The voice signal is carried in analog form from the user’s location to Company Offices (COs) using a copper twisted pair also referred to as a local loop. The analog signal is converted to digital form at the Company Offices (COs) by a codec (coder/decoder). This is followed by transmission of signals in digital form over backbone networks to the Company Office (CO) at the other end. Once transmitted the signal is