Assessment proceedings - few questions

Friends,

I have a few questions on assessment proceedings:

i)                 Whether the service of notice is a pre-condition for jurisdiction?

ii)                What is the status of a notice served beyond time?

iii)              Is it correct to contend that there is no valid service, when it is noticed so?

iv)              Can the service of notice be questioned on technical grounds?

v)               Can an irregularity in the service of notice be cured and/ or waived?

vi)              Can a defect in the notice be said as technical error?

vii)             Can an assessment, beyond the permitted time limit, could be held valid?

Please do guide me..... Thx in advance........

Regards,

Chintan