"Huh," you ask.
OK you have come to the correct place for answers.
First, though let us catch our breaths. SIP=Session Initiation Protocol. Here's a link to a good and credible explanation.
"The Rec," as I will call it, constitutes a standards-based approach for management of direct IP peering between VoIP service provider networks and SIP-enabled IP PBXs in the enterprise.
The big plus here is that once implemented in specific, branded solutions, this would eliminate the need for VoIP gateways in the enterprise. Added plusses: improved VoIP call quality and more flexible configurability for applications and rich media services.