Introduction

The objectives of this TSB are to provide end-to-end voice quality guidelines for North American IP Telephony and to an E-Model tutorial for IP scenarios. IP Telephony introduces several impairments, some of which are familiar and some new. The E-Model (ITU-T Recommendation G.107) is a tool that can estimate the end-to-end voice quality, taking the IP Telephony parameters and impairments into account. This TSB first describes how the E-Model handles IP Telephony impairments and then it provides general design recommendations for the best possible voice quality performance irrespective of cost, available technology or customer requirements. These recommendations are illustrated with specific IP scenarios to provide an E-Model tutorial for analyzing real networks.

Since initially, IP telephony is a replacement technology for the existing wireline PSTN, the focus of this document is on wireline scenarios. The impairments introduced by wireline IP packet technology can be significant. The reader should be aware that wireless and satellite technologies also introduce significant impairments and that only a few of the combined effects are illustrated here. This TSB builds on similar work done for North American PBX private networks that was published in TIA/EIA/TSB32-A and the focus of this document remains on providing guidelines for engineered private networks as opposed to the Internet.

The E-Model scenarios detailed in this TSB, are available for download as a spreadsheet tool at: http://www.e-model.org/