Fax Transmissions: What Goes Wrong

The implementation of the T.30 protocol, which the International Telecommunications Union (ITU) uses to govern fax transmissions, varies widely from one manufacturer to the next, and even from one model line of fax machines to the next.

On top of this native compatibility problem, the switched circuit public telephone network that fax was intended for is being rapidly replaced by Voice over IP, which switches data packets over the Internet. The impairment compensations built into fax for the switched circuit network actually cause problems over the switched packet network.

The outcome of all this has been an unfortunate litany of:

  • Fax calls that don’t connect with answering terminals
  • Fax calls that terminate without transferring all the queued pages
  • Receiving fax terminals that print flawed pages
  • Fax terminals that appear to send/receive all pages but turn on an error indicator
  • Fax calls that seem to take an inordinate amount of time to complete

It commonly falls to an IT or Communications manager to ‘make fax work,’ and that means finding a tool or service that can discover and analyze fax transmission problems. QualityLogic has been deeply involved in the facsimile protocol and making industry-leading tools for over 20 years.

Fax and Fax over IP Test Tools

FaxLab: Test Your System’s Interoperability

"Diagram

FaxLab addresses the interoperability problem caused by the creative interpretations of the T.30 protocol used to build fax terminals and the PSTN side of IP gateways. Using highly-detailed statistical T.30 device profiles and a comprehensive set of test calls, FaxLab plays back the behavior of real-world devices, replacing a lab full of facsimile devices with software.

FaxLab works for equipment manufacturers and provides telecom carriers with end-to-end troubleshooting. FaxLab emulates 177 V.17 and 45 V.34 fax machines, MFPs, fax modem/fax software combinations to emulate the installed base of fax systems. Its precisely crafted and recorded test calls facilitate fast, accurate problem assessments for Fax over IP networks as well as PSTN connected systems. Its reporting system covers high-level ITU Figure of Merit assessments to quickly sort failed and marginal calls from acceptable connections, as well as intricately detailed T.30 parameter values.

DataProbe: Monitor Connections

Diagram: DataProble T30/T38 testing a T.38 gateway - fax and fax over IP test tools
DataProble T30/T38 Testing a T.38 Gateway

DataProbe monitors and analyzes the protocols that are used to transfer facsimile page images. DataProbe does not generate or answer fax calls. Instead, it monitors them for negotiation issues, page transfer faults, and transport protocol problems.

Its basic T30 version, the DataProbe T30 Analyzer uses a DataTrap capture device to acquire and parse T.30 messages from analog PSTN lines and performs the same in-depth analysis that our FaxLab product employs.

DataProbe’s T30-T38 Analyzer edition will also tap SIP-managed IP fax traffic to parse T.30 messages out of G.711 packets and directly record and analyze T.38 packets.

Since it includes the T30 version’s PSTN monitoring capability, it can display ladder diagrams of the T.30 call messages vs. T.38 or G.711 packets to directly point out communications failures. For end-to-end testing, place a DataTrap at each end of the call. It can put up a ladder diagram of the complete call from originator to answerer.

Fax Test Product Distinctions

The main features of each product are listed in the table below for easy comparison.

Product Send / Receive Monitor Scripting Analysis V.17 V.34 T.38 G.711
FaxLab Yes No Yes Yes Yes Yes No* No*
DataProbe T30 No Yes No Yes Yes Yes Yes Yes
DataProbe T30-T38 No Yes No Yes Yes Yes Yes Yes

*FaxLab is commonly used for precision end-to-end fax call page exchanges to test T.38 and G.711 gateway operation.

Fax Test Services

Having trouble with fax over your IP network? We can troubleshoot your systems remotely and securely using FaxLab and/or DataProbe. We’ll perform the assessment, prepare a detailed test report, and recommend actions to correct the issue.

Facing tight deadlines? Our fax experts find issues with your product and help you resolve them quickly.  (whether it’s a fax device, MFP or fax/media gateway)

Fax Protocol Training

If you’d like to get your staff up to speed on all things fax, we can provide a two-day engineering-level training course in fax technologies. We can hold the two-day course at your site, and we also schedule periodic open classes.

Fill out the form below, or contact us to find out more.

Keep Your Fax Users Happy with QualityLogic Test Tools and Services

Want to learn more about how our QA and testing tools and services can make your job easier? Contact us to find out more.