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Definition
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.
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