This project deals with algorithm for monitoring the QoS and to detect failures in voice communication systems. Algorithm has two parts. First part is the analysis of data stored in Call Detail Records (CDR). For each call one CDR or ticket or traces is generated. These traces contain data related to the call describing the system elements involved, such as time and duration of the call, phone types and numbers, SS7 signaling, trunks, time slots, what happen to the call, etc. The tickets are generated in PSTN switches or over VoIP gateways, for the case of Internet Protocol Detail Record (IPDRs). These tickets can be used to monitor the QoS and to detect faults focusing in different aspects related to the call, such as technical, economic, or social. Second part is the calculation of Answer to Seizure Ratio (ASR), by which a communication network performance can be calculated. Our main goal is to analyze and produce the various important parameters from the CDR thereby helping the Network Performance Engineers to easily understand the performance of the network and to save their time.