For network engineering, following short-term courses may be useful:-
(a) Diploma in Computer Application and Network Administration
(b) Certificate Course in Network Administration
National Institute of Electronics & Information Technology, Ministry of Electronics & Information Technology, Government of India (website: http://beta.nielit.gov.in) conducts these courses in various cities and towns of India. These courses are recognized. Many organizations/training institutes in private sector also offer similar types of short-term courses.
However, it would not be advisable to resign considering the present less than satisfactory employment condition in IT sector. You may undergo part-time training programme in network administration, start applying for new job and resign only after you receive a better job offer in your preferred area of work, i.e., network engineering.
Caution: Explosive. Handle with care.