4. QUALITY OF SERVICE PARAMETERS FOR VoLTE SERVICES Every VoLTE Telecommunications Operator shall meet the following Quality of Service standards set for VoLTE service in respect of each specified parameter measured by test calls in any locality and shall submit a monthly report based on peak hour conditions. Table 4: Quality of Service Parameter for VoLTE Services Parameter IMS Registration Success Rate Definition Formula Target The ratio of the number of successful terminating session establishment to the number of attempted terminating session establishment for LTE network. It is used to evaluate accessibility performance provided. Registration Success Rate = (Successful registration attempts/ Total number of registration attempts) X100 Service Availability End to end service availability in terms of capacity to establish calls from, and to, a VoLTE customer. Service Availability = [(Total operational minutes - Total minutes of service downtime) / Total operational minutes] X 100 Post Dialing Delay (PDD) Time interval (in seconds) between the end of dialing by the caller and the reception back by user of the appropriate ringing tone or recorded announcement. Post Dialing Delay (PDD) = Time of ringing tone - Time of Dialing Circuit switch Fall Back (CSFB) Success Rate [%] Circuit Switch Fall Back Success Rate denotes whether the CSFB procedure ends successfully in such a way that the mobile can continue with the actual call setup signaling. Number of calls successfully established on a 4G/LTE network that are successfully switched to a 2G/3G network divided by total call attempts expressed as a percentage ≥98% success rate within 6 seconds fall back time Call Drop Rate The proportion of successfully established voice calls that are dropped by the network before they can be ended normally by the user. Call Drop Rate is the probability of a call terminating without the user causing it. Call Drop Rate = (Total number of calls terminated unwillingly / Total number of successfully established calls) X100% ≤ 2% Network Efficiency Ratio Network Efficiency Ratio means the ability of the network to deliver calls to the far terminal. It expresses the relationship between the number of seizures and the sum of number of seizures resulting in either an answer message, or a user busy or a no answer ring. Network Efficiency Ratio = (Number of seizures resulting in answer message, user busy, no answer / Total number of seizures attempt) X100% ≥ 95% 16 ≥ 90% for Urban and ≥ 90% for Rural ≥ 90% for Urban and ≥ 90% for Rural ≤ 4 Seconds for LTE to LTE ≤ 6 seconds for LTE to legacy no more than