Switch/Router Architectures

3Shared-Bus and Shared-Memory-Based Switch/Router Architectures

3.1 Architectures with Bus-Based Switch Fabrics and Centralized Forwarding Engines

The first generation of router and switch/router designs has relied upon centralized processing and shared memory for forwarding and buffering packets, respectively. These designs have traditionally been based on a shared bus switch fabric. In such designs, all packets received from all interfaces are written to a common memory pool.

After forwarding decisions are made, packets are then read from this shared memory and sent to the appropriate output interface(s). Even a majority of today's low-end or small-capacity systems (residential and small enterprise routers and switch/routers) still adopt this design. The simplicity and requirements of these systems make the shared-bus, shared-processor, and shared-memory architecture a natural fit.

Examples of this category of switch/router architectures are listed below. These example architectures are still in common use today and very much contemporary even though some were developed more than a decade ago. The goal here is to use these designs to highlight the main architectural approaches adopted and concepts developed over the years.

Example Architectures

• DECNIS 500/600 Multiprotocol Bridge/Router (Chapter 5)
• Fore Systems PowerHub multilayer switches with Simple Network Interface Modules (Chapter 6)
• Cisco Catalyst 6000 Series Switch Architectures (Chapter 7)
• Cisco Catalyst 6500 ...