thanks i will check that,we gave soft reset to that site and now the problem is solved.
As per trend of 7 days the sdcch traffic was good(no congestion) and all LAC update hysteresis is at default value.
well pix radio condition is bit poor,rx level is -80dBm to -85dBm.
But thank u all for ur valuable advices.I will keep them in mind for future.