Options for Testing Twinax Cables

Carole Warner Reece

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

4 responses to “Options for Testing Twinax Cables

  1. Hello Carole,

    We are also looking into getting some some of these cables and utilize them between new 7Ks, 5 to 7Ks, 5K, and possible 2 to 5Ks.

    Based on my research, there are two types;
    SFP-H10GB-CUxM Twinax cable, (1-5 meters are passive, and 7-10 are active)
    SFP-10G-AOCxM Active Optical Cable assembly
    *** Active cables draw power, which is how it’s able to achieve and maintain signal integrity at its longer length.

    Do you know if your colleagues are utilizing both cables? Are there any advantages between these two cables?

    Thank you,


  2. Hi Ben –

    Yes, they are using both active and passive twinax. The passive ones haven a smaller diameter and are more flexible – the active ones are bulkier. You will need entry space in the rack to pull them in.

    A nice command for checking remotely what has been installed is [b]show interface transceiver[/b]. You may see things like:

    transceiver is present
    type is 10Gbase-SR
    name is CISCO-AVAGO
    part number is SFBR-709SMZ-CS1
    revision is G4.1
    serial number is AVDxxxxx
    nominal bitrate is 10300 MBit/sec
    Link length supported for 50/125um OM2 fiber is 82 m
    Link length supported for 62.5/125um fiber is 26 m
    Link length supported for 50/125um OM3 fiber is 300 m
    cisco id is —
    cisco extended id number is 4
    cisco part number is 10-2415-03
    cisco product id is SFP-10G-SR
    cisco vendor id is V03

    transceiver is not present

    transceiver is present
    type is SFP-H10GB-ACU10M
    name is CISCO-TYCO
    part number is 2163675-2
    revision is A
    serial number is TEDxxxxxxx
    nominal bitrate is 10300 MBit/sec
    Link length supported for copper is 10 m
    cisco id is —
    cisco extended id number is 4

    transceiver is present
    type is 1000base-SX
    name is CISCO-AVAGO
    part number is QFBR-5766LP
    revision is
    serial number is AGSxxxxxxx
    nominal bitrate is 1300 MBit/sec
    cisco id is —
    cisco extended id number is 4

    transceiver is present
    type is 1000base-T
    name is CISCO-METHODE
    part number is SP7041_Rev_F
    revision is F
    serial number is 00000Mxxxxxx
    nominal bitrate is 1300 MBit/sec
    Link length supported for copper is 100 m
    cisco id is —
    cisco extended id number is 4

    . . .


  3. Caveat with Active Twinax cables… Not all NIC/CNA vendors and then respective server/appliance vendors support any Active Twinax cable. So it’s important to check with the NIC/CNA and server/appliance vendor if you need the Active cable for that longer distance (7m or 10m). Typically Active cables between network devices (switches, routers, firewalls, etc.) are supported across the board (well at least with Cisco).

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