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Telecommunications Testing: Switched Circuit to Switched Packet Fax

After 120 years of switched circuit telecommunications, the Internet upended the telephone paradigm with Voice over IP (VoIP). While telecom companies have adapted to Internet voice communications, fax transmission is still a challenge. QualityLogic’s telecommunications testing tools and services have supported fax terminal and carrier equipment development for three decades, helping telecom organizations deal with analog and digital fax, and most importantly, the boundary conditions between them.

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QualityLogic Knows Fax


QualityLogic’s award-winning FaxLab interoperability test tool replaces a lab full of fax terminals to provide telecom testing for carrier and terminal fax equipment. You get robust operation with a representative sample of the installed base of devices.

Fax Troubleshooting

DataProbe records and analyzes T.30/T.38/G.711 fax calls, providing detailed message assessment and interoperation ladder diagrams between PSTN and IP fax transport protocols.

T.30/T.38 Training

Get your team up to speed quickly with our two-day training class on the operation and troubleshooting of fax terminals and carrier equipment. Led by our principal fax engineer, this class covers the protocols and “tribal” knowledge gained over decades of hands-on experience.

Fax Service Assessment

Need to know the quality of your fax connections to the outside world? QualityLogic can provide you with a detailed assessment of configuration, connection, reliability and real-world throughput, as well as recommendations from our fax engineering staff.

Fax Over IP or Straight Up

The facsimile transmission standard is imperfect even for switched circuit operation. Getting it to work over the Internet is a struggle. The T.30 fax protocol is an ongoing issue for telecommunications because:

  • T.30 was written with wide timing tolerances to accommodate its proprietary roots, so compliance doesn’t guarantee compatibility with other compliant systems
  • Fax terminals and IP gateways implement their own interpretations of T.30, leading to interoperability issues
  • Transmission compensations designed for switched circuits are impairments for fax IP transmission
  • Fax has no built-in error correction for IP packet transmission issues
  • Troubleshooting for switched circuit or IP fax, and especially for hybrid links, requires a deep protocol understanding
Detailed investigation into our fax transmission problems was beyond the desired scope of our IT operations. Being able to bring QualityLogic in as an expert third party service was just what we needed.
Medical Center IT Director

Case Study: Medical Center Fax over IP

When this major university medical center added a new electronic record system, its fax usage increased dramatically. It saw a substantial increase in fax call trouble reports, in spite of replacing older multifunction peripherals. With fax terminal locations spread through multiple buildings across a city-wide campus, the medical center needed a coordinated, informed approach to control this problem.

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