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Some Tips on Deploying SFP+ Direct Attach Cables

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The IEEE Standard 802.3ae-2002 was ratified twelve years ago, since then, large enterprises started confidently deploying 10GbE in their corporate backbones, data centers, and server farms to support high-bandwidth, mission critical applications. SFP+ 10Gbqs assemblies representing the mainstream of 10G optical solutions, are available in both copper and fiber formats. Copper based twinax cable assemblies offer short reach options for ToR or short middle of Row (MoR) applications whereas the SFP+ fiber optics address medium to long reach applications. This article presents several tips for achieving a reliable, affordable, and simple 10 Gigabit Ethernet deployment when installing SFP+ Direct Attach Cables (DAC) in your network.

SFP+ DAC cables For Top-of-Rack Applications

SFP+ Direct Attach Cables are available in several lengths up to 10 meters (33 ft) and are the currently the best cabling option for short-reach 10 Gigabit Ethernet connections. It integrates SFP+ compatible connectors with a copper cable into a low-latency, energy-efficient, and low-cost solution. This small form factor SFP+ cables can be easily plugged in Top-of-Rack (ToR) switches providing high port density 10 Gigabit Ethernet in an efficient 1U form factor. Server and network storage vendors use 10 Gigabit SFP+ network adapters on their equipment for the same reason. The following displays one of the connectivity samples with fiber and direct attach technology.

ToR-physical-options

What’s more, DAC cables simplify rack cabling and termination. Each server and network storage device can be directly connected to the ToR switch, eliminating the need for intermediate patch panels. DAC are flexible enough for vertical cabling management within the rack architecture. The only cabling outside the rack is the ToR switch uplink connection to the aggregation layer, making moving racks easy.

Consider Cable Length

To ensure a long-term reliability, it is recommended to observe and maintain proper cable bend radius and equally important to provide adequate and secure strain relief on the cable. If the cable emerges from the rear of connector at too sharp an angle, excess mechanical stress may be transmitted both along the cable and into the circuit board located inside the connector. The following image shows am example of 3 cabinet Pod with 40 2 RU servers distributed over 3 cabinets with 2 ToR switches in center cabinet requires 80 SFP+ cables with longest cable of 4m.

Cable length deployment

Connector EEPROM

Generally SFP+ Direct Attach Copper Cable Assemblies are intelligent cables. The connector has an integrated EEPROM with information populated in registers that is provided to the active equipment when queried through an I2C bus Most active equipment port allow for interchangeable types of me to be plugged into its ports. The registers in the EEPROM provide a method for the connector to identify itself as an SFP+ passive copper module to allow the active equipment to operate in the proper mode. Other information contained in the memory registers includes vendor name, part number, serial number, and cable length in meters.

Use Cable Management

To help manage the weight of bundled cable and ensure they do not sag over time, a cable manager or strain relief bar should be installed to support 10g SFP  and provide strain relief along the horizontal plane. Strain relief bars facilitate the correct alignment of cable and connector into the port, and help installers observe manufacturer and bend radius requirements of cable close to the connector. The strain relief bars also help keep cables routed clear from spaces directly behind server and switch equipment, reducing thermal resistance through the equipment and promote effective cooling and airflow. Besides, cable ties should be used to bundle the cables together and tie them to the strain relief bars and cable managers. This should be done carefully to ensure the cables are firmly in place and will not move, but not so tight as to deform or stress the cable jacket.

Installing Tips and Practices

Besides the above tips, there are a few practical instructions that should be adhered to during installation to optimize the effectiveness of the layout:

  • For overhead cable routing, place the switches near the top of the racks
  • For under floor cable routing, place the switches near the bottom of the racks
  • Do not route SFP+ Cable Assemblies parallel to power cables, they should only cross at right angles
  • Do not route cables in front of fans or air ventilation areas of the rack
  • Do not kink cables
  • Do not twist connectors

Conclusion

SFP+ copper cables are popular in short-reach 10G applications. It offers the smallest 10G form factor and a small overall cable diameter for higher-density and optimized rack space in 10G uplinks and 10G Fibre Channel SAN and NAS input/output connections. Like the former 10GBase-CX4 optics, these cable assemblies utilize twinax cable from 30AWG to 24AWG and are available in specific lengths. Therefore the same pathway considerations should be taken into account in the design. FS.COM 10G SFP+ DAC cables are designed with reliability and compatibility to help companies support rising bandwidth requirements, new applications, and demands of a fast-paced business environment. For more information on FS.COM 10G DAC cables as well as other optical products, please contact us directly.

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