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http://www.etsi.org/deliver/etsi_gr/NFV-IFA/001_099/015/02.03.01_60/gr_NFV-IFA015v020301p0.zip (Including UML and Gendoc) <-- this is what you were looking for.
The IFA015 PDF:
http://www.etsi.org/deliver/etsi_gr/NFV-IFA/001_099/015/02.03.01_60/gr_NFV-IFA015v020301p.pdf
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