Admission to most institutes in India (like IISc/IIT ) are through GATE exam which is conducted during February every year. GATE is a common entrance for institutes like IISc/ IITs. The sale of applications and information brochures is during Septermber/October.
(summarized from http://en.wikipedia.org/wiki/User:Arvind_devaraj/Career_India)
IISc has a two year M.E program in most departments (which is called M.Tech/M.Des in other departments). For people interested in research it also has M.Sc(Engineering) programming which takes about 2 to 2.5 years. The entrance to these programmes is primarily through GATE.
There are two major research programmes (apart from M.Sc(Engg)) – Ph.D and Integrated Ph.D. Admissions for Ph.D programme is through “IISc Entrance test” which is conducted in April . Usually Ph.D programme is taken by students after completing their Masters, though some departments offer direct Ph.D to bachelors. Integrated Ph.D programme is a 5 year course (with 2 years of course work and 3 years of research work). This programme is offered mainly in science stream.
People working in companies can apply for “External Registration Programs” (ERP) . It is similar to M.Sc(Engg)/Ph.D programme. The candidate needs to spend only the first six months at the institute. Research can then be carried on from his/her company. The candidate must have atleast two years of professional experience and must have a guide at the company
Entrance to IIT M.Tech programmes is also through GATE. Depending on the GATE score, some IITs (like Kanpur) require additional tests and interview. Others give admission solely based on GATE score . GATE score can also be used to apply for (KReSIT) Kanwal Rekhi school of Information Technology  , which additionally requires a written test and interview.IIST (Indian Institute of Space Science and Technology) also offers admission through GATE.only 6 seat’s are there in each branch. all courses at IIST are wrt ISRO .Interview is conducted on the basic of Merit list(http://www.iist.ac.in) .
National Institute of Technology was previously known as Regional Engineering College (REC). Establised in 1959, there are 17 NITs in India , one each in major states. The admissions for masters in engineering is through GATE. Some of these institutes also conduct an additional exam for candidates shortlisted based on the GATE score, which will be the final selection criteria. Apart from masters in engineering some of these institutes also offer MBA, MCA, MSc(Tech) for Sciences and MSc(IT).
IIIT(M) — Indian Institute of Iinformation Technology (& Management), MHRD ministry are in Allahabad, Gwalior and Jabalpur. These are central govt. supported institutions. Others are IIIT (International School of Information Technology) which are in Bangalore, Hyderabad, Pune, Calcutta which are state govt. supported institutions. Some of these including, IIITH, IIITB, IIITA and IIITM (Gwalior) offer PG courses. The notifications for PG admissions for IIITB comes around January and last date is around the end of Jan. For IIITH the last dates are around the end of March. The selection process involves an entrance test and an interview. Data structures and algorithms, Theory of Computation are subjects that should be looked on as an important from the point of view of interviews. Though the main stress in any PG interview is on the subjects that you like the most. One should be very confident in one or two subjects, the choice of subjects is always offered in the interviews. This does not mean that you have to necessarily pursue these fields only. IIITH also offers GATE scholarships for those having a GATE score.
All the best!!!