Большая разница SNR Margin (dB) между Downstream и Upstream

[al.an]

Слишком большая разница Downstream и Upstream по Downstream линия хорошая а по Upstream близка к критической. В чем проблема?
Statistics -- ADSL
ADSL line statistics.
Mode ADSL2+
Latency Interleave
Trellis Coding Enable
Status SHOWTIME.L0
Power Level L0

Downstream Upstream
SNR Margin (dB) 17.7 6.3
Attenuation (dB) 9.5 7.0
Output Power (dBm) 12.5 6.5
Attainable Rate (Kbps) 23128 264
Rate (Kbps) 9999 263
K (number of bytes in DMT frame) 27 12
R (number of check bytes in RS code word) 16 12
S (RS code word size in DMT frame) 0.08 22.66
D (interleaver depth) 224 1
Delay (msec) 4.81 5.66
FEC 648 0
CRC 0 0
Total ES 0 0
Total SES 0 0
Total UAS 0 0