Cisco Systems It used to be reasonable to expect that any two points connected to the Internet to have the ability to hold any communication. Such an expectation has not be reasonable for quite some time, thanks to firewalls, NATs, and other intermediate devices. Today, we acknowledge a new architecture and we name the functional blocks of that architecture as well as several ways to get ends to communicate, and how two devices could expect to communicate with each other. This document does not define the protocols involved.