Method and device for determining a parameter that characterizes a number of spare positions to be used for cancelling the crosstalk of lines joining a digital subscriber line vectoring group

Method for determining a parameter that characterizes a number of spare positions to be used for cancelling the crosstalk of lines joining a digital subscriber line vectoring group, the vectoring comprising cancelling the crosstalk caused by a maximum number of lines of the vectoring group and reserving said number of spare positions, wherein the method comprises

• determining at least one residual crosstalk metric that depends on a residual crosstalk between at least two subscriber lines of the vectoring group, wherein the residual crosstalk metric includes at least one crosstalk ratio of a certain line, the crosstalk ratio corresponding to a ratio of the crosstalk caused by the lines of the vectoring group that are not included in crosstalk cancellation to the crosstalk caused by all lines of the vectoring group;
• and
• determining said parameter that characterizes the number of spare positions depending on the at least one residual crosstalk metric by successively modifying the number of spare positions until the residual crosstalk metric fulfils a termination condition,
• wherein the method comprises checking whether or not the residual crosstalk metric is less than a predefined residual crosstalk threshold and depending on the result of said checking either successively incrementing the parameter until the residual crosstalk metric fulfils a first predefined termination condition or successively decrementing the parameter until the residual crosstalk metric fulfils a second predefined termination condition.