New-Tech Europe | April 2018

transceiver shells in copper and optical technologies such as: Direct Attached Copper (DACs) Active Optical Cables (AOCs) Optical transceivers Mellanox’s LinkX product line offers a full set of DAC and AOC cables as well as multi-mode and single-mode optical transceivers used in data center networks. Mellanox designs and manufactures its own DAC cables for 25G and 50G signaling used in 25/50/100G and 50/100/200G cables and transceivers. In addition, the company designs its own switch, network adapter and multi-mode transceiver silicon ICs as well as systems and transceivers. Let’s take a quick look at each type of interconnect features and benefits on why they are so popular in modern data centers. Since large enterprise, HPC, artificial intelligence and hyperscale data centers may deploy cables and transceivers in the tens of thousands, the first concern is minimizing costs at every point. Interconnects are all about linking at various speeds and reaches so there are a myriad of different products optimized for each common reach deployed. Direct Attached Copper (DACs) Cables DAC cables are a complete plug & play cable and forms a direct electrical connection, hence the name, typically between switches and network adapters in a system rack. DACs use shielded coaxial copper wires, a simple PCB, and a shell enclosure to form the complete cable. This is the lowest cost means of creating a link but at high data rates, the data signals turn into radio waves and leave the wire which limits DAC cable usage to <5meters using 25G signaling. Mellanox DAC cables are built to the highest standards with a bit error rating about 1,000 times better than

image 1: One System Row in a Massive Google Data Center Source: Google

Active Optical Cables (AOCs)

the IEEE industry standard. DAC cables dominate inside the rack interconnects today and have displaced almost every other form of link. Offering near zero power consumption and zero latency delays, with advancing CMOS IC line widths in switches and adapters silicon for new SerDes along with new cable materials, DAC cables promise to be around well into the 100G-per-lane era in the mid 2020s.

AOCs convert the electrical data signals into a pulsing laser connected to optical fibers. Using a large core diameter fiber, called “multi-mode”, the alignment of the laser with the fiber is low cost and optical signals can reach 100meters. AOCs are typically used to link top-of-tack switches to other switches in the network starting at 3 meters and extending to about 30

image 2: All Internet Traffic Ends in a Server Passing Through Copper and Optical Links

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