It's just airway flying with position reports on HF.
Mumbai wants estimates for all your points within the FIR and at the end of the initial position report give them your SELCAL code.
Be sure to monitor air-to-air frequency 123.45. Mumbai will sometimes have another aircraft contact you on VHF and you can relay your position report via them.
Entering Maldives FIR you are right on the limit of their VHF coverage - it may take 10 minutes after entering their FIR before you can contact them.