Hello,

In BTech 3rd year CSE department you have to study many more subjects. Like compiler design, computer network, computer organization and architecture, database management system,  environmental studies, linear algebra, software engineering, theory of computation. These are basically main subjects of 5th and 6th sem CSE department. I'll suggest you some good author for these subjects book below

1. Computer networking- I.A Dhotre and D.S. Bagad

2. Network design- A. M Jones

So many books are available for those subjects. You can know more some of your professors and seniors also.

All the best.