VoIP Voice and Fax Signal Processing

13.1 BASIC TEST SETUP

Figure 13.1 shows the basic voice quality measurement setup with two VoIP gateways. Each gateway is shown with multiple foreign exchange subscriber (FXS) interfaces. Based on the testing, one gateway could be of a known third-party reference. Voice calls are made within each gateway and between two different gateways. Several comparisons can be derived with these combinations. At the first level, several manual calls and observations can be made. To test the TR-57 transmission requirements given in Chapter 1, in the test setup, Sage communication test instruments are connected to each gateway on the FXS interface. In addition to TR-57 tests, Sage instruments are used to extract several telephone parameters such as singing return loss (SRL), echo return loss (ERL) and idle channel noise. In Fig. 13.1, the AI-5120 telephone line tester is shown in series with multiple phones. The instrument AI-5120 measures signal, timing, tones, and call features analysis by monitoring and storing several waveforms based on the events and call progress. Multiple parallel phones on the same interface helps in evaluating the ringer equivalence number (REN) characteristics.

Table 13.1. Classification of VoIP Tests

Classification of test	Suggested instruments
VoIP manual tests	This is to make several first-level observations based on the listening tests and IP packet analysis
End-to-end voice transmission similar to TR-57 tests of North America	Sage-935AT, Sage-960, ...