Many of you’re acquainted with the 40G BiDi pluggable optic, but did you know the 40G CSR may serve similar use situations and may also be an attractive alternative?

As network operators increase their link bandwidth from 10G to 40G, they have to choose between two types of 40G pluggable optics: The ones that require ribbon fiber or the ones that use duplex fiber via superior transceiver technology. The benefit of a duplex MMF (Multi-Mode Dietary fiber) 40G optic is that’s uses exactly the same fiber wire infrastructure as 10G SR optics. As a result, upgrading from 10G to 40G will not require new dietary fiber cabling.

Quite a few years ago Cisco introduced the “40G BiDi” (Bi-Directional) QSFP+ short-reach optic (QSFP-40G-SR-BD), which uses duplex MMF. Recently Cisco introduced the QSFP+ “40G CSR” optic (QSFP-40G-CSR-S), which operates upon duplex MMF at 40G and contains longer reach also.

Reach benefit of the QSFP+ 40G CSR

For reaches beyond 150m, the 40G CSR optic is a great option to 40G BiDi, since it provides connectivity around 400m over duplex MMF. This kind of fiber is quite common in apps including:

• Business: 40G optical online connectivity between distribution switches and wiring closet switches.
• Data Center: 40G optical hyperlinks between leaf and spines switches.
• Service Provider: 40G optical hyperlinks connecting switches, routers, along with other platforms

The 40G CSR provides extended reach optical connectivity of 400m over OM4/OM5 and 300m over OM3 using SWDM (Shortwave Wavelength Division Multiplexing) technology, as the 40G BiDi provides connectivity of 150M over OM4/OM5 and 100m over OM3 using 2x20Gbps PAM4 (Pulse Amplitude Modulation) bi-directional technology.

Comparison between 40G CSR and 40G BiDi

As the two optical transceivers use different technology they each supply 40G connectivity in the QSFP+ form factor and so are on the market, as shown in the next comparison:

On-going great things about 40G BiDi

The 40G BiDi is still a fantastic choice for applications requiring:

• Optical monitoring utilizing the receive-just 40G BiDi (QSFP-40G-BD-RX) pluggable optic
• Interoperability with the dual-price 40/100G BiDi (QSFP-40/100G-SRBD) pluggable optic

With Cisco Optics, you have several choices for 40G MMF wire infrastructure.

Additional Resources:

The Optics-to-Device compatibility matrix

Complete collection of Cisco pluggable transceivers from 1Gbps to 400Gbps

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