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Which type of MPO to MPO cable do I need for my transceiver?

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TitleWhich type of MPO to MPO cable do I need for my transceiver?
Question
Which type of MPO to MPO cable do I need for my transceiver?
Environment
  • EXOS
  • 100Gb
  • 40Gb
  • 100G QSFP28 SR4 MMF (8 core)
  • CRP2 100GBASE-SR10 (20 core)
Answer
Parallel fiber polarity types required for Ethernet applications depends on the fiber topology being used. There is no one answer and, at least for laser optimized OM3 and OM4 MMF, doesn’t depend on speed.  Distance may be different for 40Gb and 100Gb, but Ethernet fiber MPO polarity is independent of speed for Ethernet applications.  The basic requirement is always to deliver the Tx fiber positions on one transceiver to the Rx fiber positions on the other transceiver (and vice versa) – but this can be done in a couple of different ways.
 
For a connection between two MPO optical transceivers using a single patch cord between transceivers – i.e. no patch panels or cassettes in the fiber path - with either 12 or 24 fiber (8 or 20 fibers used for Ethernet) you would use a Type B cable.  Type B provides for a reverse of the Ethernet Tx and Rx fiber positions in a key up – key up orientation of the cable to deliver the Ethernet Tx fiber positions on one end to the Rx fiber positions on the other end.   This configuration tends to be commonly used so the 10345 and 10346 MPO 12 fiber patch cords we offer are Type B.  24 fiber MPO used for SR10 is analogous – use a Type B for a single patch cord connection.
 
However, if you are going through a patch panel or cassette structured wiring infrastructure, then “it depends”.  Structured wiring may or may not provide the reverse of the fiber positions within the cabling plant itself so the customer must, in this case, know what has been deployed in their fiber plant.  There are different conventions that customers could have adopted.  Depending on the infrastructure, the customer may require Type A patch cords on each end or a Type A on one end and a Type B on the other – again, depends on how their structured wiring was implemented.  Type A cabling can be thought of as a straight through cable with no reverse of the fiber positions in a key up – key up cable orientation.
 
The only definitive statement we can make is that for 40Gb or 100Gb Ethernet parallel fiber applications, one would never ever (ever) use type C cabling anywhere in the fiber path.  Type C is used to transport duplex fiber connections across a high density parallel fiber infrastructure, so would never be compatible with 40Gb or 100Gb Ethernet fiber polarity requirements.  Type C is not compatible with 40Gb or 100Gb breakout applications either and implements different fiber pairing than used for Ethernet breakout.
 
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