###### Abstract
DSL technology still holds its position among access technologies even with advances in competing access technologies such as DOCSIS, WiMAX, Long Term Evolution (LTE) and Gigabit Passive Optical Network (GPON) [18]. The new G.fast recommendations specify 1 Gbps over metallic access. To achieve such high bit rates, G.fast uses only the last part of the existing metallic access network and cable wiring on the premises. These conductors are usually unshielded, unconditional twisted pairs, flat pairs or quadriceps (four twisted wires) and are known for strong crosstalk, especially inside fours. Achieving high bit rates with such a low-quality metallic transmission medium is a challenging task that requires a novel approach. G.fast-based access networks uses the FTDP architecture, which contains a DPU unit connected to a CO unit via an optical fiber. DPU units are installed close to customer premises, usually in mini cabinets mounted in basements of multi-dwelling units, or on electric poles, curbs or maintenance holes, and are connected to CPE equipment via homogeneous symmetric line pairs. Impulsive noise is the bottleneck that limits the distance at which DSL communications can take place [19]. Because DSL systems' performance is severely restricted by the occurrence of impulsive noise, there are various techniques to mitigate impulse noise, which presents severe performance impairments [20]. In [21], authors analyzed the performance of dual-sensor-based interference cancellation schemes for downstream DSL systems. The most common cause of DSL line errors is the presence of faults and interferences. The use of loopback qualification testing prior to activation of a DSL line may allow the DSL line to function without significant line defects for at least some time after the start of its operation. However, the symmetric copper pair, as a transmission medium, is very susceptible to the presence of diverse types of failures and interferences that can arise in operation due to several different causes. In practice, there are the fewest types of failures and the least types of influences. The presence of disturbances and interference can manifest itself in separate ways on the functioning of DSL lines and completely diverse types of failures and interferences affect the functioning of DSL lines in an equivalent way. By shortening the length of DSL lines and installing ADSL2+ or VDSL devices, extremely high bit rates, up to hundreds of Mbps, can be transmitted. Currently, high demands are placed on the transmission speeds and transmission of broadband services (e.g., IPTV [22] and Video over DSL [23]), where the provided service essentially works without restrictions. If there is already a service outage, timely and accurate diagnosis of the DSL line must be ensured. The physical layer parameters of DSL transceivers describe the DSL line functionality where electrical parameters of the metallic pair describe the quality of the homogeneous symmetric line as a medium for transmitting a digital signal. The provision of broadband services is related to Quality of Service (QoS), which directly describes the quality of the service provided [24]. Currently, the most widely used procedure for testing services in metallic homogeneous lines is the DSL Quality Management (DQM) loop principle. This testing is based on the collection of data for relevant parameters, e.g., signal transmission and degradation of QoS parameters [11; 25]. For reach extension of conventional DSL systems, Long-Reach DSL (LR-DSL) technologies are the focus of attention in the present. As such, advanced signal processing techniques are expected for elimination of the Inter-Symbol Interference (ISI) and the Inter-Carrier Interference (ICI) between the carriers of the same symbol. A more efficient way to deal with extended loop lengths using a channel shortening filter, commonly referred to as a Time domain Equalizer (TEQ), is presented in [26] together with new constraints for upstream scenarios.