[Serusers] Deploying VoIP on a WAN

Hi, As many of you may know, we are undertaking several tests in order to test the interoperability between several PBX IP from different vendors. Until now, we were trusting that the VoIP IP PBX were good enough to be interconnected directly, however, one of the vendors have presented the "SBC" concept. The "SBC" (Session Border Controller) is not a new concept since we were using it anyway when we setup a (Asterisk+SER+SIP Proxy) Box to handle the "on-net dialout" calls. I'm now overwhelmed with the amount of SBCs that are suggested by the vendors to implement a solution. (http://www.juniper.net/solutions/literature/solutionbriefs/351085.pdf) Can anyone drop me some lines about this? I urgently need some feedback on this. Thanks! Joao Pereira www.fccn.pt