What is POC ?
so you’re measuring a high SDCCH failure rate on “all” cells, during each hour of a day, every day of a week ?
Is it related to the amount of traffic in your network ? (for instance, during the night, there is no traffic, so you don’t see sdcch failure, do you ?)
If the failures happen all the time, even when there is no traffic, you might be getting some country wide interference (another operator ?).. or possibly some problem with other sites collocated on the same pole (did you co-locate your gsm900 sites with dcs1800 sites ?)
If the failures only happen when TCH traffic is occurring, then you can investigate parameters settings (i’m thinking about timers and repetition of RACH…)
Just giving some leads, about BSS side. I’ve got no knowledge about NSS side.