Belkin Wireless G+Mimo ADSL2+ Modem Router
ADSL
Type Fast
Status No Defect

Downstream Upstream
Data Rate(Kbps) 1536 512
Noise margin (dB) 30.3 26.0
Output power (dBm) 12.1 17.7
Attenuation (dB) 28.0 13.5

This is my normal readings for router
after some time noise margin drops significantly
reset router (hard or soft) -- sometimes few times -- returns to normal

what's the problem? line or router?