The Role of Optics and Electronics in High-Capacity Routers

This paper examines the role of optical and electronic technologies in future high-capacity routers. In particular, optical and electronic technologies for use in the key router functions of buffering and switching are compared. The comparison is based on aggressive but plausible estimates of buffer and switch performance projected out to around 2020. The analysis of buffer technologies uses a new model of power dissipation in optical-delay-line buffers using optical fiber and planar waveguides, including slow-light waveguides. Using this model together with models of storage capacity in ideal and nonideal slow-light delay lines, the power dissipation and scaling characteristics of optical and electronic buffers are compared. The author concludes that planar integrated optical buffers occupy larger chip area than electronic buffers, dissipate more power than electronic buffers, and are limited in capacity to, at most, a few IP packets. Optical fiber-based buffers have lower power dissipation but are bulky. The author also concludes that electronic buffering will remain the technology of choice in future high-capacity routers. The power dissipation of high-capacity optical and electronic cross connects for a number of cross connect architectures is compared. The author shows that optical and electronic cross connects dissipate similar power and require a similar chip area. Optical technologies show a potential for inclusion in high-capacity routers, especially as the basis for arrayed-waveguide-grating-based cross connects and as components in E/O/E interconnects. A major challenge in large cross connects, both optical and electronic, will be to efficiently manage the very large number of interconnects between chips and boards. The general conclusion is that electronic technologies are likely to remain as integral components in the signal transmission path of future high-capacity routers. There does not appear to be a compelling case for replacing electronic routers with optically transparent optical packet switches