40 Gb/s and 100 Gb/s Ethernet Short-Reach Optical and Copper Host Board Channel Design

Since its inception in the early `70s, Ethernet has gradually displaced other popular standards, such as token-ring, while becoming the de facto standard for local area networks in the enterprise office and data center environments. During Ethernet's lifetime, data rates have increased from the original 10 Mb/s to 10 Gb/s. Now, 40 Gb/s and 100 Gb/s standards have been defined, ushering in the next generation of equipment and components. This article presents the challenges of designing 40 Gb/s and 100 Gb/s Ethernet host board channels that are targeted for data center applications. The data center infrastructure comprises: a short-reach optical multimode fiber of length 100 m or less; and/or a copper twinax shielded cable of length 7 m or less, to interconnect collocated communication equipment racks. The recently published 40 Gb/s and 100 Gb/s Ethernet standard specifies the copper interfaces (CR4/CR10) and the short-reach optical non-retimed optical interfaces (SR4/SR10). This article reviews the Ethernet copper and fiber short-reach application compliance test techniques, and identifies common specifications and areas of divergence for both applications. Cable specifications and its insertion loss budget are also reviewed, providing conclusions that will aid the communications equipment and components manufacturer with a clear reference to address the design and implementation of a standards-compliant product.