Modern Optical Data Centers: Design Challenges and Issues

The modern optical data centers are facing bottleneck conditions due to humongous data generated by modern user applications. By 2020, the peak traffic is estimated to be around 400 P bytes/s transfer rate at a very low power consumption of 20 MW and even less around 2 MW for optical interconnections. Thus, there is a need to shift from Electronic Packet Switching (EPS) techniques to route data through the core network. In EPS, the headers are processed by electronic controllers, thereby; EPS suffers from limitations of data transfer rate threshold among core routing nodes. Due to high packet overheads, there is a significant rise in physical and link-level losses alleviating congestion at core routers. These aforementioned limitations could be addressed by deploying optical switches in core switching networks through Optical Packet Switching (OPS) and Optical Burst Switching (OBS) techniques. The switch controller needs to route data optically and in parallel, control decisions are handled by electronics. The advantages of deploying OPS and OBS are higher bandwidth, low latency, and limited link-level losses. However, data signals routed through these optical switches suffer from electrical to optical (E/O) conversions at ingress and Optical to Electrical (E/O) conversions at egress nodes, respectively. Thus, the advantages of deploying optical fiber at the core network are mitigated. All-Optical Switches (AOS) routes data optically from end-to-end addressing the above need. Fabrication of AOS is difficult in reality due to the non-availability of optical components like Tunable Wavelength Converters (TWCs) and Optical RAM. Thus, the design of an all-optical switch is of paramount importance. Motivated by the aforementioned discussions, the paper discusses a systematic survey of OPS, OBS, and AOS designs with their pros and cons. The paper also bridges the gap between previous notable optical switch designs and current switch designs which could route optical packets at high bandwidth and minimum delay. Finally, the concluding remarks are provided.