DCN April 2016 - Page 17

cabling limitation of just 5m-7m, these direct attach assemblies are restricted for use with ToR switch configurations where smaller access switches are deployed in each equipment cabinet and directly connected to the equipment in that cabinet. While SFP+, QSFP and other twinaxial cable assemblies support low power and low latency, which can be ideal for supercomputing environments, there are some considerations. Standards based Category 6A and higher cabling supports autonegotiation. Direct attach twinaxial assemblies do not. Autonegotiation is the ability for a switch to automatically and seamlessly switch between different speeds on individual ports depending on the connected equipment, enabling partial switch or server upgrades on an as-needed basis. Without autonegotiation, a switch upgrade requires all the servers connected to that switch to also be upgraded, incurring full upgrade costs all at once. Unlike Category 6A and higher cabling that works with all Base-T switches, regardless of speed or vendor, higher cost proprietary direct attach twinaxial cable assemblies may be required by some equipment vendors for use with their ToR switches. Proprietary cabling assemblies can require cable upgrades to happen simultaneously with equipment upgrades. In other words, currently installed direct attach cable assemblies will likely need to be replaced if another vendor’s equipment or a higher speed switch is deployed. Some ToR switches are even designed to check vendor security IDs on the cables connected to each port and either display errors or prevent ports from functioning when connected to an unsupported vendor ID. With recent advancements in technology now enabling 10GBase-T switches to drop in price and power consumption, standards based Category 6A cabling or higher makes the most sense for today’s switch-to-server connections in the data centre. Another reason to stay with standards based cabling for switchto-server connections at the edge stems from the fact that switch-toserver connection speeds continue to push beyond 10Gb/s and ISO/ IEC has already initiated work on next generation cabling to support upcoming IEEE 802.3bq 25 and Today’s flattened architectures with fewer switch tiers result in longer cable runs between switches. 40Gb/s Ethernet (ie. 25GBase-T and 40GBase-T) over balanced twistedpair copper cabling. 25GBase-T and 40GBase-T both build on the existing and well established 10GBase-T technology and are intended for operation over 30m of future ISO/IEC Class 1 cabling constructed from Category 8.1 components and Class 2 cabling constructed from Category 8.2 components characterised to 2GHz. Class 1 and Class 2 cabling will continue to share open and common specifications, ensuring interoperability and backwards 17