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100G CLR4 White Paper

Intel Leads the Formation of the 100G CLR4 Alliance to Standardize Transceivers for 100G CWDM Data Centers.

On April 1st, Intel announced the formation of the 100G CLR4 Alliance.

Intel created the CLR4 Alliance because several of Intel’s customers came to us and requested Intel to help develop an industry standard to address several missing and much needed features for 100G single-mode, optical transceivers to support next-generation data centers.

The 100G CLR4 Alliance’s mission is to create an open, multi-vendor specification for a cost-effective, low-power, 100G-CWDM optical transceiver in QSFP form factor with a reach of up to 2 km over duplex single-mode fiber. 


In the past, optical transceivers have traditionally been used and designed for the telecom infrastructure.  But now, with the advent of large and hyper-scale data centers becoming very popular, the combinations of low power-consumption, high port-density, long reach, and low-cost are now extremely important.

Implementing in a 3.5 Watt QSFP28 form factor is highly desired by switching companies as their systems will be built using this form factor with 32-36 QSFP ports in a 1RU switch system.

CWDM enables using only two single-mode fibers, which is the least cost, longest reach solution. 

What is It?

The CLR4 Alliance will specifically focus on specifying:

  • 4-channel, 25G, 100G optical transceiver
  • Based on 1310nm wavelengths
  • With a ­+ 20nm CWDM wavelength spacing
  • Using single-mode fibers
  • Fiber reach for up to 2 km
  • Duplex LC optical connectors
  • In a 3.5 Watt QSFP28 form factor

Why is It Needed?

Andy Bechtolsheim, CTO and Founder of Arista Networks, is very vocal about the situation saying, “We are announcing our 100G next-generation switch today at Interop in Las Vegas, and there are virtually no 100G QSFP28 optical transceivers available that meet the 3.5 Watt and 100 m-to-2 km reach requirements. For leaf/spine architectures, popular in big cloud systems, virtually all links are 300 m-to-2 km in length." He also said, “I fear that the current fragmentation of the 100 m-2 km optical transceiver space and slow development will stall the entire 100G industry forming in 2015 and the industry can not afford to wait any longer”.

The members of the IEEE 802.3.bm standards body were not able to agree on a singular technology standard after 2 years of review. Since then, several independent groups have formed their own standards effort around specific technologies leaving the market highly fragmented and not addressing the specific needs for the next-generation cloud, HPC enterprise, and telecom data centers.

About the CLR4 Alliance

The 100G CLR4 Alliance is a standard setting effort open to all participants and designed specifically to create an industry standard around the specific product requirements for the next-generation data centers using 100G optical transceivers at a reach of up to 2 km. Unlike traditional Multi-Source Agreement (MSA) efforts, Intel has formed an Alliance that does not require legal agreements, fees, intellectual property, or other restrictions in order to participate. It may evolve into an MSA at some point and combine with other MSA efforts but time is not on the industry’s side and the situation is becoming urgent.

Mario Paniccia, Intel Fellow and GM of the Silicon Photonics Solutions Group commented, “We are pleased to help the industry on developing an Open specification for this optical link. We were surprised at how strong of a response we received. In the span of only 2 weeks, 26 companies announced they will participate in the Alliance. The list continues to grow and includes big cloud system operators, switching system companies, and optical transceiver companies from majors to startups. Several supporters could not lend their public support in time for the announcement. The Alliance is open to all to participate in and is in line with the current 'open' trends in the data center industry.”

What is Next?

In April, Intel will post various drafts of the technical specifications and solicit comments from supporters to arrive at a common specification sometime in May 2014.

More Information

100G CLR4 Alliance Innovators

See who the CLR4 innovators are.

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100G CLR4 Information

Get an overview of what CLR4 is.

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