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2/11
2014
Carole Warner Reece

Options for Testing Twinax Cables

One of my colleagues asked me if I knew what he could use to test Cisco twinax cables – specifically the SFP-H10GB-CUxM passive cables, and the SFP-H10GB-ACUxM active cables.  These cables are identified in the industry as SFP+ direct-attach copper cables, and can be used to interconnect Nexus switches and other devices at 10GE. He has recently connected a bunch of them in his data center.

I looked into it a bit – these cables use the Etherent Alliance’s SFF-8431 and SFF-8461 standards. Specifically, SFF-8431 for the Passive Twinax cables, and SFF-8461 for the Active Twinax cables.

Based on my reseach, I think the practical answer is no – there is just not a simple ” yes, good cable / no, bad cable” hand-held tool for Cisco twinax cables. For example, I spoke with Cisco, they do not have a test tool. I spoke with Fluke, they don’t have an module that accepts the Cisco twinax cables. I spoke with CableandKits – they don’t have a tester either. I also talked to CDW, who looked internally, and called around their associates. They don’t have a hand-held tester, or know of anyone who does.

I did see that Tektronix gear was previously used for testing the SFF-8431 standard in Etherent Alliance’s SFP+ Direct Copper Attach Interoperability paper, so I asked them as well. Tektronix said you could use a DSA8300 sampling oscilloscope with a 80E04 TDR module and 80SSPAR software to test the cable. They said that there is some learning curve to it, but that a local account manager could demonstrate how to use it properly. However, this is probably more advanced then most end users will want. These tools would give you a frequency response graph and impedance and reflections, but not a simple Pass or Fail test.  fwiw, these components have a  list price of about $64,000, so while technically possible, it appears to be too expensive to be a practical solution for most end users.

Workaround: I recommended to my colleague that since all the twinax cables are 1m – 10m, he should probably reserve two ports on adjacent Nexus gear, configure them to be up, and just hook a suspect cable up between the two “active” ports and see if it works.

— cwr

Twitter: @cwreece

Carole Warner Reece

Architect

A senior network consultant with more than fifteen years of industry experience, Carole is one of our most highly experienced network professionals. Her current focus is on the data center and on network infrastructure.

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