An entry Visa is essential for all foreigners visiting India. Those entering primarily for 2021 IEEE ISPCC will need to apply for Conference Visa. Those whose primary purpose is tourism may apply for a Tourist Visa.
Conference Visas are issued by the relevant Indian Embassy if participants are able to produce: 

• 1. A letter of invitation to the conference/seminar/workshop in India
• 2. Relevant copies of permissions from Indian Government Agencies for the staging of a particular conference
• 3. THE CONFERENCE ORGANIZERS WILL SEND THESE DOCUMENTS BY EMAIL ONLY TO AUTHORS WHO HAVE REGISTERED FOR THE CONFERENCE AND HAVE NO PAYMENTS PENDING

It is advisable to apply for Visas well in advance, but not earlier than 3 months before the date of the Conference. Foreign visitors entering India must possess a passport valid for at least 6 months after their date of entry into India, except in the case of nationals of Bhutan and Nepal, who need only carry suitable means of identification. 

Visitors from Afghanistan, China, Iran, Iraq, Pakistan and Sudan must apply for their Visa at least 45 days in advance. AUTHORS FROM THESE COUNTRIES ARE ADVISED TO REGISTER FOR THE CONFERENCE EARLY SO THAT INVITATION LETTER AND PERMISSION DOCUMENTS CAN BE SENT TO THEM BY THE CONFERNCE ORGANIZERS IN TIME. 

If approved, a single entry Conference Visa will be granted. Please note that the validity of a Visa begins on the day it is issued. The date of entry into India does not affect the period of validity of a Visa. The rules change regularly, so you should check you have the most up to date information for your trip.
The list of Indian diplomatic missions overseas can be consulted at
http://mea.gov.in/indian-missions-abroad.htm

Some Indian embassies and consulates have outsourced their visa processing services to VFS Global http://www.vfsglobal.com

On-line Visa application form may be filled up at http://indianvisaonline.gov.in