Datasheet
40G Cabling Technical Q&A Document
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of connector for MTP-12 cables but this does not exist in the market for single-mode fiber. APC is
the only available choice for single-mode MTP-12 fiber.
Q. Can a customer use third party QSFP+ to QSFP+ and SFP+ cables?
A. Arista does not restrict the use of third party copper cables. These cables need to comply with
the IEEE specifications, to allow them to be correctly recognized by the Arista switch. Interfaces
with cables not recognized correctly will be disabled.
Q. What is the minimum bend radius of the 40G copper cables?
A. The QSFP-SFP (4-way) CR4 cables have a stated minimum bend radius of 32.35mm (1.27”) to
ensure they are not damaged. The QSFP-QSFP cables have a stated minimum bend radius of
45mm (1.77”) to ensure they are not damaged.
[QSFP-QSFP cables are thicker than the QSFP-SFP ones and need more space.]
Q. How does the QSFP+ to SFP+ fiber convertor allow 4x 10G?
A. The IEEE 40G-SR4 standard specified a parallel technology, with 4 lanes in each direction. The
purpose of this was to allow for easier development of 40G, re-using 10G components. As a side
result the 40G multi-mode transceivers can also support 4x10G modes. (The switch or router also
has to support this in both the hardware and software). A fiber that connects from one 40G port to
four 10G ports provides a physical path to allow the source “40G” port running in 4x10G mode to be
connected to 4 unique 10G destinations. As the fiber is a passive medium it has no concept of the
40G or 10G signals.
Q. Where does a customer buy the special splitter cables?
A. First, this is not really a special cable - it is an MTP-LC cable as shown below. This product is an
8f assembly with the polarity of the fibers in a specific order in order to provide the correct
orientation of the fibers into the channels:
A large number of cabling companies have the MTP-LC cables available and are supplying these in
volume to customers. However, these are usually a special order, as the total cable length, tail
lengths and cable polarity are customer selectable. As a result these are commonly considered as
“special” but are in fact standard cables, custom ordered.