I'm wondering what purpose of port mapping in nBAR, how and when it is used during packet inspection. Why port maches are needed when deep packet inspection is done anyway.
For example, if I'm accessing web page with port 666 (http://www.example.org:666) and my port-map is left in default state how those http packets will be clasified by nbar?
Port mapping with NBAR is usually done to add support for protocols that are not currently supported by a match protocol statement. It extends the ability of NBAR to match any custom traffic you want matched that NBAR currently does not support.
There is a detailed page of NBAR port mapping and PDLM's at http://www.cisco.com/warp/public/105/custompdlms.html
Hope this helps.