VoIP technology has some basic requirements: Reliability (specified grade of service) is maintained without too much overhead. In PSTN, the required grade of service is maintained whereas in TCP/IP networks it is not guaranteed. VoIP demands maintaining a specific grade of service. IP networks should meet performance requirements. In TCP/IP networks, packet delivery is not ensured, so for supporting voice over IP, special protocols are required. Similarly, signalling must be compatible with the PSTN. Since the voice over IP infrastructure has to be integrated with PSTN, it is necessary to provide compatibility in signalling. Again, the PSTM/VoIP network must be match together in appropriate gateways. In addition to that, the network management, security aspects have to be comparable to that of PSTN.

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