I am attaching the notes which i prepared for the subject "DATA COMMUNICATION SYSTEMS" according to JNTU syllabus..
Check them out to see if they are useful. The details of the topics covered in the unit are listed in the first page of every document. If u like my post, reply me and i will post the others too.. All the 8 units links are given below.. feel free to let me know if u need anything else. i will do my best to help..