High availability VoIP solutions with distributed fault tolerance

Availability refers to one's ability to access a service. Whether the service is a network completing a phone call, an ATM dispensing cash, delivery of electricity into a home, or one protocol layer providing information to another, the user of the service expects that the requested service is available when required. In the telecommunications industry, high-availability of a service is typically referred to when a service is available 99.999% of the time ("five-nines"), meaning the service is unavailable only about five minutes per year. This level of service has become the standard all vendors must meet when selling carrier-grade solutions for high-availability networks.