The nature of the public network has changed. Demand for Internet Protocol (IP) data is growing at a compound annual rate of between 100% and 800%1, while voice demand remains stable. What was once a predominantly circuit switched network handling mainly circuit switched voice traffic has become a circuit-switched network handling mainly IP data. Because the nature of the traffic is not well matched to the underlying technology, this network is proving very costly to scale. User spending has not increased proportionally to the rate of bandwidth increase, and carrier revenue growth is stuck at the lower end of 10% to 20% per year. The result is that carriers are building themselves out of business.
Over the last 10 years, as data traffic has grown both in importance and volume, technologies such as frame relay, ATM, and Point-to-Point Protocol (PPP) have been developed to force fit data onto the circuit network. While these protocols provided virtual connections-a useful approach for many services-they have proven too inefficient, costly and complex to scale to the levels necessary to satisfy the insatiable demand for data services. More recently, Gigabit Ethernet (GigE) has been adopted by many network service providers as a way to network user data without the burden of SONET/SDH and ATM. GigE has shortcomings when applied in carrier networks were recognized and for these problems, a technology called Resilient Packet Ring Technology were developed.
RPR retains the best attributes of SONET/SDH, ATM, and Gigabit Ethernet. RPR is optimized for differentiated IP and other packet data services, while providing uncompromised quality for circuit voice and private line services. It works in point-to-point, linear, ring, or mesh networks, providing ring survivability in less than 50 milliseconds. RPR dynamically and statistically multiplexes all services into the entire available bandwidth in both directions on the ring while preserving bandwidth and service quality guarantees on a per-customer, per-service basis. And it does all this at a fraction of the cost of legacy SONET/SDH and ATM solutions.
Data, rather than voice circuits, dominates today's bandwidth requirements. New services such as IP VPN, voice over IP (VoIP), and digital video are no longer confined within the corporate local-area network (LAN). These applications are placing new requirements on metropolitan-area network (MAN) and wide-area network (WAN) transport. RPR is uniquely positioned to fulfill these bandwidth and feature requirements as networks transition from circuit-dominated to packet-optimized infrastructures.
RPR technology uses a dual counter rotating fiber ring topology. Both rings (inner and outer) are used to transport working traffic between nodes. By utilizing both fibers, instead of keeping a spare fiber for protection, RPR utilizes the total available ring bandwidth. These fibers or ringlets are also used to carry control (topology updates, protection, and bandwidth control) messages. Control messages flow in the opposite direction of the traffic that they represent. For instance, outer-ring traffic-control information is carried on the inner ring to upstream nodes.