RTNR application in the AT&T network

The introduction of Real-Time Network Routing (RTNR) into the AT&T Switched Network was completed in July 1991, and completely replaced dynamic nonhierarchical routing (DNHR). It has resulted in a marked improvement in network connection availability while simultaneously reducing network costs. RTNR has laid the foundation for an important service and quality advantage by introducing new class-of-service capabilities and dramatically improving network service and robustness, particularly in responding to abnormal traffic or failure conditions. RTNR provides the platform for the dynamic class-ofservice routing features for emerging new services, and also provides a multiple ingress/egress routing arrangement to ensure reliability and flexibility for international and access networks. To date 10 virtual networks have been established to serve major classes-ofservice, which share the facilities of the network but provide individual control and monitoring of traffic as well as new priority service capabilities. RTNR allows a marked improvement in network reliability by providing for the selection of over 135 routes between every pair of cities for every call.