VoIP Voice and Fax Signal Processing

15.10 VoIP FAX TESTS

A fax test with VoIP is more complex than testing a few fax pages between two fax machines in PSTN. The ITU has provided an umbrella series with the ITU-T-E.450 recommendations for fax quality tests, out of which ITU-T-E.453 and E.458 [ITU-T-E.453 (1994), ITU-T-E.458 (1996)] classify fax image quality and call success and E.453 [ITU-T-E.453 (1994)] addresses transmission-induced scan line errors. Instruments incorporate these ITU recommendations for fax quality measurements. The fax tests listed in this chapter are broadly classified as listed below:

• Testing with multiple fax machines that include
  • Instrument-based fax tests, QualityLogic® FaxLab® (Moorpark, CA) as a tool that emulates multiple facsimile vendors and other fax testing instruments working as multiple fax machines
  • Multiple types of physical fax machines
  • Computer used as a fax machine
• Interoperability tests
• Fax testing with data traffic
• Network impediment tests in a combination of multiple fax machines and VoIP gateways

15.10.1 Testing with Multiple Fax Machines

Several types of fax machines are available worldwide. Fax machines before 1996 had some deviations in implementation compared with the most recent revision of the standards. Most of these deviations will not create a problem on PSTN-based systems mainly because of lower end-to-end delay and synchronized end-to-end digital transmission. In VoIP-based fax, these deviations can create fax call failures caused by increased delays in end-to-end ...