Switch/Router Architectures

2Understanding Shared-Bus and Shared-Memory Switch Fabrics

2.1 Introduction

One of the major components that define the performance and capabilities of a switch, switch/router, router, and almost all network devices is the switch fabric. The switch fabric (both shared or distributed) in a network device influences in a great way the following:

1. The scalability of the device and the network
2. The nonblocking characteristics of the network
3. The throughput offered to end users
4. The quality of service (QoS) offered to users

The type of buffering employed in the switch fabric and its location also play a major role in the aforementioned issues. A switch fabric, in the sense of a network device, refers to a structure that is used to interconnect multiple components or modules in a system to allow them to exchange/transfer information, sometimes, simultaneously.

Packets are transferred across the switch fabric from input ports to output ports, and sometimes, held in small temporary “queues” within the fabric when contention with other traffic prevents a packet from being delivered immediately to its destination. The switch fabric in a switch/router or router is responsible for transferring packets between the various functional modules (network interface cards, memory blocks, route/control processors, forwarding engines, etc.). In particular, it transports user packets transiting the device from the input modules to the appropriate output modules. Figure 2.1 illustrates the generic architecture ...