Scalable electronic packet switches

Due to the changed economic environment, the rush to implementing packet switches with switching capacities above 1 Tb/s, which had proceeded at a frantic pace for some years, has slowed down considerably. Most service providers do not foresee the deployment of switches and routers with gigantic capacities in the near future. The immediate interest does now rarely go beyond the subterabit range, with a sweet spot between 120-640 Gb/s, where the emphasis is on feature-rich systems that enable the convergence of legacy services with new emerging data services. Although the current focus is on smaller switches, it is still relevant to understand their evolution path to multiterabit capacities. The scalability issues are also critical to reduce complexity and simplify implementation, in order to push the limits of what can be achieved in the switches within current economic and market constraints. We analyze the current state of the art of practical large packet switches and routers, and discuss the issues affecting their scalability. Our approach is pragmatic, with most of our attention devoted to three major scalability aspects: implementation, support of quality of service, and multicasting. After a general discussion of these issues, we show their impact on the most popular switch architectures.