Of a civilisation, מנוונת means "degenerate" but of a network I think either obsolete or obsolescent would do to indicate that it is out of date, no longer current.

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Note added at 1 hr (2010-09-20 15:37:33 GMT)
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A couple of examples:

http://aceproject.org/main/english/et/etd06.htm

http://www.cmcauk.co.uk/obsolescence_monitoring.php?gclid=CP...


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Note added at 1 hr (2010-09-20 15:46:31 GMT)
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There is actually a concept of degeneracy in networking, so it is even possible that the correct translation may be "degenerate network"

http://portal.acm.org/citation.cfm?id=1148663.1148698

http://www.springerlink.com/content/j5727956q1637g33/

In fact, I think, in view of the choice of word in Hebrew, I now think it likely that the correct answer should be degenerate network. If you select my reply, please use "degenerate network" for the glossary entry.