Hello Ashu,

Few of the best online courses for CS and related field are :

NPTEL Courses - http://nptel.iitm.ac.in/courses/106101007/

Operating Systems - http://webcast.berkeley.edu/#c,d,Computer_Science,-XXv-cvA_iCrnl0625nXp4GimjT-cv_1

Algorithms - https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-006-introduction-to-algorithms-fall-2011/index.htm

Computer Networks - https://f12.class2go.stanford.edu/networking/Fall2012

All the best!