As far as I understood from the change-log of Asterisk 11.5.0 it’s supports the PRACK on the sip.
I installed this version on Centos 5.4 32bit.
I added to the sip peer configuration prack=yes.
But it’s not working.
Few months ago I installed Asterisk 1.8 darjeeling of Olle, and it’s worked ok with the prack.
But now i’m looking for oficial version.