A New Way to Deploy 40G Ethernet? Cisco’s BiDi

In early November, Cisco launched its Application Centric Infrastructure (ACI).  ACI includes a new line of Nexus 9000 series switches, a new version of NX-OS and a policy controller called Application Policy Infrastructure Controller (APIC).  We at Panduit were proud to be a part of the launch.

As a part of that launch, Cisco announced a new technology for deploying 40G Ethernet that has so far, received little attention.  Cisco calls that technology BiDi.

BiDi is shorthand for “bi-directional”.  BiDi uses two different wavelengths on the same fiber, with one wavelength headed in one direction and the second wavelength traveling in the other direction.  The advantage with Cisco’s 40G BiDi is that it can use the same 10G infrastructure to implement 40G Ethernet.

10G Ethernet (10GBASE-SR) uses two multimode optical fibers and duplex LC connectors for transmitting on one of the fibers and receiving on the other fiber.  40G Ethernet (40GBASE-SR4) uses 8 multimode optical fibers; 4 for transmitting data and 4 for receiving data.  This requires the use of 12-fiber trunks and patch cords terminated with MPO connectors. However, with 40G Ethernet only using 8 out of the 12 fibers in a 12-fiber trunk, this results in ⅓ of the total bandwidth available to a data center disappearing when migrating from 10G to 40G Ethernet.

There are ways to reclaim the dark fiber, such as using 40G migration cassettes or harnesses.  One could also add more fiber to the infrastructure to maintain the total aggregate bandwidth.  Regardless, migrating from a 10G infrastructure to 40G can be expensive and time consuming.

BiDi represents a new way to deploy 40G Ethernet that meets all 40GBASE-SR4 performance criteria. BiDi provides 40G Ethernet on two multimode fibers and duplex LC connectors, just like the existing 10G infrastructure that is deployed today.  With 40G BiDi, migrating from 10G to 40G is straightforward: Replace the existing 10G optical modules with 40G BiDi optical modules.  There is no need for expensive 40G migration cassettes, and no need to add additional fiber infrastructure.

In order for 40G BiDi to be a replacement for 40GBASE-SR4, it has to meet the same QSFP+ form factor, electrical interface, and reach targets.  (Those reach targets are 100m using OM3 fiber, and 150m when using OM4 fiber.)  However, since two different wavelengths are used, one can only reach out to 125m if using OM4, with it being an engineered link with a total insertion loss of 1.0db.  Clearly, this does not help 40G BiDi optical modules to supplant 40GBASE-SR4 modules.

Working with Cisco, Panduit’s Fiber R&D team investigated what the reach could be using Panduit’s Signature Core™ Fiber Optic Cabling System, the next generation of multimode optical fiber. Through extensive modeling and testing, the Fiber R&D team determined that the maximum reach for an un-engineered link when using Signature Core is 150m.

Cisco’s 40G BiDi optical modules offer another way to deploy 40G Ethernet: it is less costly to implement 40G Ethernet using two multimode fibers (vs. the 8 fibers required by 40GBASE-SR4) and Panduit’s Signature Core Fiber Optic Cabling System gives BiDi the reach out to 150m.

Click here to learn more about our Signature Core Fiber Optic Cabling System.  To learn more about Cisco’s BiDi optical modules, click here.

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