Intrusion Prevention requirements document

All,

I work on a team that manages signature and behavioral based intrusion 
detection systems today.  We have been tasked with reviewing IPS (or whatever 
vendor name acronym you prefer) in '06.  Our normal process is to put together 
a base requirements document to weed out vendors in the first round through a 
paper excercise and then bring in the best we can identify.  My question is, 
has anyone developed a matrix that identifies key qualifiers in an IPS solution 
(e.g. in-line, fails open/closed, reporting features, etc.).  If so, could you 
provide links or the documents?

If not, what categories are most significant to consider in your expert 
opinions?  What reasons did you choose the solution you have?  What would you 
consider if you had to choose over again, etc?

Thanks in advance for your responses.

VT

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