Digital subscriber line (DSL) technology, often referred to as “broadband”, is a family of services that provides high speed digital data transmission over the metallic twisted copper pairs that form part of a local telephone network. DSL is commonly used to provide a customer's home with a network connection, typically to the Internet via an ISP.
Some DSL lines, especially longer rural lines, are susceptible to interference resulting in instability in the connection. A DSL line can lose synchronisation when the noise on the line is so large that the data (signal) being transmitted cannot be processed correctly. Line management techniques can help address this problem and stabilise a line at the expense of a lower synchronisation rate. One such technique is known as Dynamic Line Management DLM.
DLM measures the line parameters, such as the error rates and train/resynchronisation events, and adjusts line configuration parameters accordingly to try and stabilise the line, which has the effect of reducing the synchronisation rate. DLM applies one of a limited number of profiles to the line to improve the stability. This is typically achieved by setting a target signal to noise ratio margin, or target SNR margin, which affects the maximum rate the line can synchronise at. A high target SNR margin will result in a more stable line, and a low target SNR margin a less stable line (all other factors being equal). The effect is more pronounced on problematic or longer lines.
The profiles applied by DLM are limited in the sense that only a small number of relatively coarse target SNR margins are used. An example of the range of target SNR margins typically used might be 3 dB, 6 dB, 9 dB, 12 dB and 15 dB. These coarse steps in target SNR margin can result in relatively large changes in the resulting synchronisation rate. Thus, for longer lines in particular where the synchronisation rate is usually quite low, relatively large changes in synchronisation rate are not desirable and can result in an overly large reduction in the synchronisation rate.
European patent application EP2237462 describes a method for dynamic line management, where the signal to noise ratio is compared to a threshold, and resynchronisations are forced on the line accordingly.
US patent application US2005/0237940 describes a system for adaptively applying a target noise margin to a DSL line. In the approach described, the target noise margin is increased for the line until it runs error free from the influence of impulse noise.