A method for operating a vectored VDSL line group comprising a plurality of VDSL lines, each VDSL line comprising a DSLAM coupled to customer premises equipment, the plurality of VDSL lines comprising a first VDSL line comprising a first CPE coupled to the DSLAM, the method comprising: transmitting test signals from the DSLAM to the first CPE; the first CPE receiving test signal output data based on the test signal input data: the first CPE collecting decimated test signal output data for a subset of DSL tones in each of a plurality of DSL tone microbands, wherein each DSL tone microband contains a plurality of DSL tones in a DSL tone frequency band used for downstream transmission of data on the first DSL line, and further wherein each DSL tone subset contains not more than four DSL tones in each microband; the first CPE transmitting the decimated test signal output data to the DSLAM; generating, by a vectoring processor coupled to the DSLAM, quantized FEXT data from the decimated test signal output data by smoothing the decimated test signal output data to reduce measurement errors and/or to reduce the precision of the decimated test signal output data; generating, by the vectoring processor, losslessly coded FEXT data from the quantized FEXT data by applying a linear predictor to the quantized FEXT data and thereafter applying Golomb coding; generating, by the vectoring processor, FEXT cancellation coefficients based on the losslessly coded FEXT data; and a vectoring control entity of the vectored VDSL line group performing vectored DSL processing for the vectored VDSL line group based on the FEXT cancellation coefficients. transmitting test signals from the DSLAM to the first CPE; the first CPE receiving test signal output data based on the test signal input data: the first CPE collecting decimated test signal output data for a subset of DSL tones in each of a plurality of DSL tone microbands, wherein each DSL tone microband contains a plurality of DSL tones in a DSL tone frequency band used for downstream transmission of data on the first DSL line, and further wherein each DSL tone subset contains not more than four DSL tones in each microband; the first CPE transmitting the decimated test signal output data to the DSLAM; generating, by a vectoring processor coupled to the DSLAM, quantized FEXT data from the decimated test signal output data by smoothing the decimated test signal output data to reduce measurement errors and/or to reduce the precision of the decimated test signal output data; generating, by the vectoring processor, losslessly coded FEXT data from the quantized FEXT data by applying a linear predictor to the quantized FEXT data and thereafter applying Golomb coding; generating, by the vectoring processor, FEXT cancellation coefficients based on the losslessly coded FEXT data; and a vectoring control entity of the vectored VDSL line group performing vectored DSL processing for the vectored VDSL line group based on the FEXT cancellation coefficients. the first CPE collecting decimated test signal output data for a subset of DSL tones in each of a plurality of DSL tone microbands, wherein each DSL tone microband contains a plurality of DSL tones in a DSL tone frequency band used for downstream transmission of data on the first DSL line, and further wherein each DSL tone subset contains not more than four DSL tones in each microband; the first CPE transmitting the decimated test signal output data to the DSLAM; generating, by a vectoring processor coupled to the DSLAM, quantized FEXT data from the decimated test signal output data by smoothing the decimated test signal output data to reduce measurement errors and/or to reduce the precision of the decimated test signal output data; generating, by the vectoring processor, losslessly coded FEXT data from the quantized FEXT data by applying a linear predictor to the quantized FEXT data and thereafter applying Golomb coding; generating, by the vectoring processor, FEXT cancellation coefficients based on the losslessly coded FEXT data; and a vectoring control entity of the vectored VDSL line group performing vectored DSL processing for the vectored VDSL line group based on the FEXT cancellation coefficients.