When a 180 (Ringing) is received without a 183 (Session Progress) the phone does not emit any ringback tone thud giving no feeedback about the status of the ongoing call.

Steps to fix:

• Use the status code provided by pjsip (pjsip_status_code.PJSIP_SC_RINGING && pjsip_status_code.PJSIP_SC_PROGRESS) through CallInfo class within the onCallState method of SipCall class to discrimintate between the 180 and 183 as the status is the same (pjsip_inv_state.PJSIP_INV_STATE_EARLY).

• When the scenario matches the faulted one, it instatiates and starts a new ToneGenerator [Android] , otherwise checks if the TG is started and stops it