Joining of CA firm for articleship after CPT

Hello Friends 

Please guide me on below 2 points

1. after passing CPT examination to start CA Training , whether CA Firms are being alloted by ICAI or own source of joining is also welcome by ICAI...or both the options are valid in this professional study 

2. as per syllabus 3 yrs of article training is mandatory to appear CA Final exam. my question is whether, it (3 yrs) will be counted from " cpt passout joined articleship" or "IPCC passout joined articleship"

looking forward your earliest responses which help me out a lot...

Thanks