Voice over Internet Protocol (VoIP) and other time critical communications require a level of availability much higher than the typical transport network supporting traditional data communications. These critical command and control channels must continue to operate and remain available in the presence of an attack or other network disruption. Even disruptions of short duration can severely damage, degrade, or drop a VoIP connection. Routing protocols in use today can dynamically adjust for a changing network topology. However, they generally cannot converge quickly enough to continue an existing voice connection. As packet switching technologies continue. to erode traditional circuit switching applications, some methodology or protocol must be developed that can support, these traditional requirements over a packet-based infrastructure. We propose the use of a modified overlay tunneling network and associated routing protocols called the Fault Tolerant Overlay Protocol (FTOP) network. This network is entirely logical; the supporting routing protocol may be greatly simplified due to the overlays's ability to appear fully connected. Therefore, ensuring confidentiality and availability are much simpler using traditional cryptographic isolation and VPN technologies. Empirical results show for substrate networks, convergence time may be as high as six to ten minutes. However, the FTOP overlay network has been shown to converge in a fraction of a second, yielding an observed two order of magnitude convergence time improvement. This unique ability enhances availability of critical network services allowing operation in the face of substrate network disruption caused by malicious attack or other failure.
