While 51 service providers have fully met the benchmark of 99 per cent call success rate, Bharti and BSNL failed to meet the criteria falling below 90 per cent in certain circles.

Bharti Cellular in Maharashtra and Goa and BSNL in Maharashtra, Himachal Pradesh, Kerala and Karnataka were below the 90 per cent mark. There has been deterioration in the performance of these providers in the circles compared to the last quarter, TRAI said in its quality of service survey for the quarter ending September.

Even in call drop rate performance, all companies except Reliance and BSNL have met the benchmark. The call drop rate performance has been met by all companies except Reliance in Bihar, BSNL in Assam, Himachal Pradesh and Haryana.

Compared to the previous quarter, the performance of these service providers has deteriorated in the circles mentioned, it said.

Billing complaints per 100 bills issued were found to be within norms for 49 operators, the survey said, adding the worst offenders were Hutchitson Essar in Uttar Pradesh (East) and Andhra Pradesh, Tata Telecom in Mumbai & Maharashtra and BSNL in Punjab, Karnataka, Kolkata, Maharashtra and Kerala.

The Authority has taken note through its own monitoring system of performance deterioration in some areas of mobile services.

The mobile operators have not been able to expand their network and related infrastructure like call centres on a pace at which they were increasing the subscriber base, the survey said, adding that this had resulted in increase in network congestion, billing problems and deterioration in the performance of customer care centres.

The authority had called senior management of mobile service operators for discussions. The points emerging from these discussions have been taken note of and actions have been initiated.

These include auditing of the billing systems of service providers, monitoring the action plan for improving performance of individual operators. The authority is now following this up with individual operator-level discussions.