nachi,
your explanations are not very clear for me.. as far as i understand, you have low CSSR (high SDCCH drop) in the DCS1800 band and a longer SDCCH duration in the GSM900 band.
this is occuring on all cells ?
i would need to know your cell planning topology, your parameters and other KPI.. I need to know about the handovers 900/1800, call setup, layer definitions, frequency planning… basically, you need to offer me a trip to your country so I can have a good look to it 🙂 i sincerely doubt I can solve this over the internet… maybe someone else can.