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1 Intellectual Property Due Diligence
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2 -----------------------------------
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3
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4 Modems and voice coding are heavily patented areas. Implementing these without
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5 serious consideration of IP issues would be foolish. This document describes
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6 the basis on which the software has been implemented.
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7
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8
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9 A check of the intellectual property information at the ITU web site shows a
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10 number of patent claims against the current standards implemented by spandsp.
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11 It is important to realise, however, that some of these patents have long
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12 since expired (group III fax dates back to the 1970s). Also, many are
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13 related to recent additions to the FAX standard, such as colour FAX handling,
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14 which few people ever use.
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15
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16 The V.14 rate adaption standard seems free of patent encumberance.
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17
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18 One patent is listed as relevant to the V.17 standard. It is a patent from
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19 IBM, but the ITU database does not specify its nature. I believe it is
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20 related to the trellis coding used, and I think it has expired. I do not
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21 know for sure. The techniques used in the implementation should be free of
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22 patent encumberance. Most of the implementation is similar to the V.29
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23 modem. The key addition the trellis code processing. The trellis encoding
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24 is trivial. The decoding uses Viterbi techniques, which are quite old.
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25
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26 The V.21 standard dates from the 1950s. The V.23 standard is also very old.
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27 There is no possibility that any patents related to it are still in force.
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28 However, the implementation also needs to be free of patented techniques.
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29 The implementation only uses very mature numerical oscillator and quadrature
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30 correlation techniques, so there should be no patent issues.
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31
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32 Only one patent is listed as relevant to the V.29 standard. This dates from
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33 the 1970s, and must have expired. The modem has been implemented using only
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34 very mature techniques, none of which can be less than 20 years old. There
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35 seem no possibility, therefore, that any patents are still in force related
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36 to the techniques used.
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37
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38 Some aspect of the V.8 standard seems to have patents associated with it,
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39 according to the ITU patent database. I am unclear what these are. V.8 is a
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40 very simple standard. There seems to be nothing innovative about it.
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41
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42 Many patents are listed as relevant to the T.30 standard. However, they all
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43 appear to relate to newer features, such as colour FAX, added in recent years.
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44 The current implementation only covers the original features from the late
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45 1970s, where there appear to be patent issues.
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46
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47 The T.4 standard defines the image compression and decompression techniques
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48 used for group 3 FAXes. The spandsp implementation is based on code derived
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49 from freely available implementations of T.4. These have existed for a number
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50 of years without IP issues. The standard is old enough for any patents to have
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51 expired, anyway.
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52
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53 V.42bis compression uses the LZW algorithm. This is the same algorithm used in
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54 GIF files. Unisys patented this algorithm. However, the Unisys patent has now
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55 expired.
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