forked from Mirrors/freeswitch
56 lines
2.9 KiB
Plaintext
56 lines
2.9 KiB
Plaintext
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Intellectual Property Due Diligence
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-----------------------------------
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Modems and voice coding are heavily patented areas. Implementing these without
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serious consideration of IP issues would be foolish. This document describes
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the basis on which the software has been implemented.
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A check of the intellectual property information at the ITU web site shows a
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number of patent claims against the current standards implemented by spandsp.
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It is important to realise, however, that some of these patents have long
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since expired (group III fax dates back to the 1970s). Also, many are
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related to recent additions to the FAX standard, such as colour FAX handling,
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which few people ever use.
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The V.14 rate adaption standard seems free of patent encumberance.
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One patent is listed as relevant to the V.17 standard. It is a patent from
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IBM, but the ITU database does not specify its nature. I believe it is
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related to the trellis coding used, and I think it has expired. I do not
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know for sure. The techniques used in the implementation should be free of
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patent encumberance. Most of the implementation is similar to the V.29
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modem. The key addition the trellis code processing. The trellis encoding
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is trivial. The decoding uses Viterbi techniques, which are quite old.
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The V.21 standard dates from the 1950s. The V.23 standard is also very old.
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There is no possibility that any patents related to it are still in force.
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However, the implementation also needs to be free of patented techniques.
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The implementation only uses very mature numerical oscillator and quadrature
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correlation techniques, so there should be no patent issues.
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Only one patent is listed as relevant to the V.29 standard. This dates from
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the 1970s, and must have expired. The modem has been implemented using only
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very mature techniques, none of which can be less than 20 years old. There
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seem no possibility, therefore, that any patents are still in force related
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to the techniques used.
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Some aspect of the V.8 standard seems to have patents associated with it,
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according to the ITU patent database. I am unclear what these are. V.8 is a
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very simple standard. There seems to be nothing innovative about it.
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Many patents are listed as relevant to the T.30 standard. However, they all
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appear to relate to newer features, such as colour FAX, added in recent years.
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The current implementation only covers the original features from the late
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1970s, where there appear to be patent issues.
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The T.4 standard defines the image compression and decompression techniques
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used for group 3 FAXes. The spandsp implementation is based on code derived
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from freely available implementations of T.4. These have existed for a number
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of years without IP issues. The standard is old enough for any patents to have
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expired, anyway.
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V.42bis compression uses the LZW algorithm. This is the same algorithm used in
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GIF files. Unisys patented this algorithm. However, the Unisys patent has now
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expired.
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