Voice over the Internet Protocol (VoIP) has enjoyed a great deal of recent industry press coverage and considerable commercial acceptance as well. A recent analysis of North American Residential VoIP Markets from Frost & Sullivan, indicated that market revenue totaled $295.1 million in 2004 and expects to reach $4,076.7 million in 2010. With some justification, its supporters market VoIP as the future of telecommunications; supplanting switched circuit network connections as quickly as the hardware is built and deployed. Since VoIP solutions are being marketed as replacements for switched circuit connections, they must replicate all switched circuit capabilities and that requires compatibility with fax transmissions.

The presence of millions of fax machines installed around the world, combined with their ease of use and acclimated user base, has made fax resistant to the encroachments of email and other newer technologies. Facsimile transmission, or fax, has existed in one form or another for over a century. In its early incarnations, fax messages were sent over telegraph lines, then migrated to the switched circuit telephone network in the early 1900’s. Fax transmission’s next half-century was marked by a steady acceleration of technological development:

1935 – fax transmission becomes sufficiently robust to be sent over regular phone lines.

1963 – faxing over the Public Switched Telephone Network (PSTN) authorized by the FCC

1968 – the Carterphone Decision authorizes connection of third party (not Bell Telephone) equipment directly to the PSTN

1978 – the FCC issues its Part 68 regulations

1980 – CCITT issues a series of fax protocol definitions culminating in the Group 3 fax recommendation (T.30)

With the opening of the regulatory gates, and the creation of fax transceivers on single integrated circuit chips in the mid ‘80s, the stage was set for the mass use of fax machines.

The push to wider acceptance and use of fax lead to the introduction of Error Correction Mode (ECM) in 1988. This made possible the introduction of color fax, high speed V.34 modulation and Internet fax. However, it did not address the most basic facsimile problem, interoperability. The lack of manufacturer-to-manufacturer interoperability delayed the widespread acceptance of these technologies for years. In fact, color and Internet fax are still slimly represented and only a basic implementation of V.34 is widely available.

With the near simultaneous appearance of VoIP and V.34 fax in the market, VoIP designers were faced with a design conundrum. How were they to verify a VoIP system’s basic interoperation and its interoperation with a V.34 fax device without the ability to verify the proper operation of the V.34 fax system?

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