Summary

It is recognized that IP-based networks are increasingly used to deliver voice services to customers. These networks can impact the end-to-end service quality perceived by users. In order to maintain network performance required to deliver the desired service quality, several operational issues have to be considered. These issues include defining network performance measures and their objectives, interworking issues between networks employing a variety of technologies, network measurement points, information to be exchanged between network operators, etc.

ITU-T Study Group 13 on "Next-generation networks" has defined four key scenarios to be considered in their IP framework document:

–           Scenario a: A voice call from an IP terminal connected to an IP-based network to a PSTN phone;

–           Scenario b: A voice call from a PSTN phone to an IP terminal connected to an IP-based network;

–           Scenario c: A voice call from a PSTN phone to another PSTN phone via an IP-based network;

–           Scenario d: A voice call from an IP terminal connected to an IP-based network to another IP terminal connected to an IP-based network via PSTN.

This Recommendation focuses only on Scenario c. In Scenario c, both ends are PSTN (telephone) terminals and connected to PSTN at least as a local access (PSTN-IP-PSTN architecture). This network architecture is employed or planned to be employed by many ROAs all over the world. In this case, the user may not be aware of the changes in the underlying technology and the QoS expectations may be expected to remain the same.

This Recommendation is for providing the general aspects of voice services in PSTN-IP-PSTN architecture, especially, for providing information whether or not the existing ITU-T Recommendations could be applicable to PSTN-IP-PSTN voice architecture. Also, it covers the general impacts of IP networks to voice services and provides an overview of the performance measurement/management scope.