An obvious improvement to the single CPU design is the introduction of more independent processing power. One way to achieve this is to connect clusters of routers by using conventional LAN technology and routing protocols. Each router in the cluster is required to perform only switching and route-calculations within the bounds of a single-CPU router design.
This approach is similar to that used in parallel processing supercomputers. Unfortunately, even with modern routing protocols, RISC processors, and high-speed LAns, the use of generic networking components to connect routers does not provide the level of integration needed by most network managers. Administrational overhead of such router clusters is high, and the protocols used for general-purpose network connectivity are inefficient and inflexible.
The necessary refinement may involve a generic high-speed switching fabric, connecting line cards with peer computational capabilities. However, such multiprocessor designs are inherently complex to design and debug, as well as expensive to build. It has taken some time for vendors to develop such packet switches, and it has taken time for network providers to accumulate the traffic levels that require these sophisticated systems.
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