About The T.38 Interoperability Testing Lab Discussion Forum

What does this database do?

This database is the repository for information learned during interoperability testing in Commetrex' T.38 Interop Lab. To get started, a user may simply browse through discussion topics. This is particularly useful for new participants of the program who need to come up to speed on important issues that the group is working on. The history of discussion about these issues is preserved in this discussion database.

What is T.38?

T.38 is the ITU standard governing real-time fax relay over IP networks. Just as with data modems, fax can be transported by IP networks without a relay engine (proprietary or otherwise), provided the network is very high performance with low packet loss, delay, and jitter. Without T.38, a gateway will sense that a modem (fax or data) call is being initiated, and switch from, possibly, a low-bit-rate vocoder to G.711 (64,000 bps, full-duplex).

As long as the packets can be reassembled at the far end and streamed out to the receiving modem isochronously, the session will be successful. But that's a big if. The use of a T.38-compliant relay enables a gateway to withstand several seconds of packet delay, lost packets, and packets in error without creating errors in the received image. For the same reasons, the TIA and the ITU are working on V.MoIP, a standard for real-time data-modem relay, which should be "determined" later this year.

Moreover, products claiming compliance with H.323 Version 4 must support T.38 for real-time facsimili. As stated in the standard, the use of T.38 is mandatory, as indicated by the use of the term "shall":

This presents vendors with a problem: Although G.711 produces high-error-rate faxes, it has the benefit of interoperability. T.38 produces clean faxes, but presents an interoperability problem. T.38, having been been released in 1998, is a relatively new standard without widespread interoperability. A service provider that intends to use T.38-capable gateways from multiple vendors cannot assume interoperability. This prompted Commetrex to found the T.38 Interop Lab to provide the industry with a clearing house for testing and the posting of results. A vendor will be able to visit this forum to quickly learn whether a product has been tested. Why does this T.38 Interoperability Testing Lab exist and who can participate?

Many T.38 developers need an effective and efficient way to check their product's interoperability with other T.38 products. Developers want to make sure that their product meets basic ITU standards. Commetrex' testing lab is available at no charge to equipment developers with a shipping product. And it's logical that Commetrex, having more field-tested fax-technology experience than any other company in the industry, lead in this effort to help T.38 go mainstream, speeding the adoption of IP-based real-time fax for carrier and equipment developers. Commetrex offers a high degree of granularity in its trace diagnostic tracking because its terminating T.38 product (TerminatingT38), which is used in the testing process, is instrumented to provide the highest degree of diagnostic assistance. And, Commetrex' experienced testing team is aware of the subtle inconsistencies that only a trained eye could catch during interoperability testing.

How does the program work?

Because testing is done over the public Internet, no planes, trains, or cars are required. IP addresses are exchanged eliminating the need for on-site testing. Trace and debugging logs are frequently run with continual analysis by a senior engineer until all faxes sent are completely clean. TerminatingT38, Commetrex' award-winning T.38 product, is used to send faxes through the participant's gateway. Testing engineers analyze sessions and timing, noting any interoperability problems or other potential problems that might be in violation of basic ITU T.38 standards. Testing details are generated into a report that is sent to the participant upon completion of the program, with general testing information posted in this forum.

For more information on the testing process, click here.

Who will use this database?

Members participating in Commetrex' T.38 Interoperability Testing Program and those considering participation.


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