R-Series failover appliances allow Asterisk users and integrators to build fully redundant communications systems. These failover appliances handle the physical redirection of PSTN circuits in the event of a catastrophic hardware or software failure. Tightly integrated with monitoring and resource management software, the R-Series can switch PSTN traffic within seconds of a service interruption. A pair of Asterisk-based servers, cross-connected through an R-Series failover appliance, can achieve 99.99% availability at a fraction of the cost of other redundant phone systems solutions. The R850 provides failover capabilities for digital circuits.