Hi. I'm a student taking computer engineering. I would like to ask about call flow in airtel and the whole process involving GSM. I need help on this for my report.

Bharti Airtel Limited is an Indian global telecommunications services company based in New Delhi, India. It operates in 18 countries across South Asia, Africa, and the Channel Islands. Airtel provides GSM, 3G and 4G LTE mobile services, fixed line broadband and voice services depending upon the country of operation. It is the largest mobile network operator in India and the third largest in the world with 325 million subscribers. Airtel was named India's second most valuable brand in the first ever Brandz ranking by Millward Brown and WPP plc.

Airtel is credited with pioneering the business strategy of outsourcing all of its business operations except marketing, sales and finance and building the 'minutes factory' model of low cost and high volumes. The strategy has since been adopted by several operators. Airtel's equipment is provided and maintained by Ericsson and Nokia Solutions and Networks whereas IT support is provided by IBM. The transmission towers are maintained by subsidiaries and joint venture companies of Bharti including Bharti Infratel and Indus Towers in India. Ericsson agreed for the first time to be paid by the minute for installation and maintenance of their equipment rather than being paid up front, which allowed Airtel to provide low call rates of ₹1/minute (US$0.02/minute).