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Optics Use Cases for 40 Gigabit Ethernet Connectivity

Optics Use Cases for 40 Gigabit Ethernet Connectivity

The 40 Gigabit Ethernet (GbE), used in today’s networks as the preferred spine uplink technology, has become commonplace in data centers. With the rise of 40GbE QSFP+ optics market, various of optics solutions are available, which offer users a lot of flexibility in connectivity. Today, I am going to summarize some 40 Gigabit fiber optic connection use cases of several types of commonly used 40GbE QSFP+ optics.

Case One: QSFP+ to QSFP+ Direct Connectivity

For 40GbE to 40GbE connectivity, namely the interconnection between two QSFP+ ports, users can use different optics and cables options according to different transmission distances.

40GbE direct connectivity

  • For distances of up to 7 meters: QSFP+ to QSFP+ DAC (Direct Attach Copper) cables
  • For distances of up to 100 meters: QSFP+ to QSFP+ AOC (Active Optical Cable) or 40GBASE-SR4 QSFP+ transceiver with OM3 multimode fiber with MTP/MPO connectors or OM4 multimode fiber with MTP/MPO connectors (up to 150 meters)
  • For distances of up to 300 meters: 40GBASE-CSR4 QSFP+ transceiver with OM3 multimode fiber with MTP/MPO connectors or OM4 multimode fiber with MTP/MPO connectors (or up to 400 meters)
  • For distances of up to 1 kilometers: 40GBASE-PLRL4 QSFP+ transceiver can be used with single-mode fiber with MTP/MPO connectors
  • For distances of up to 10 kilometers: 40GBASE-LR4 QSFP+ transceiver can be used with single-mode fiber with LC connectors

Tips: The standard QSFP+ MTP/MPO connector is 12-fiber connector, but use 8 out of 12 fibers.

Case Two: 40GbE to 10GbE Ports Breakout

As we know, 40GbE ports can be used either as a single port or turned into four 10GbE ports. Thus, you can use so-called QSFP+ breakout or fan-out cables with QSFP+ on one side and four SFP+ on the other side to increase the number of available 10GbE ports.

In general, according to different distance requirements, the basic three types of solutions are available:

40GbE breakout connectivity

  • For distance of up to 5 meters: QSFP+ to SFP+ DAC Breakout Cables
  • For distance of up to 100 meters: QSFP+ Breakout AOCs
  • For distance of up to 300 meters: MTP/MPO to 4xLC Duplex OM3/OM4 multimode fiber breakout cables (mpo to lc duplex breakout cable) with the 40GBASE-CSR4 transceiver

Tips: When connect to networking switches or to server adapters which support SFP+ fiber optic connectivity, the QSFP+ DAC breakout cables are always the preferred option.

Case Three: Deploy 40GbE With Existing 10GbE Cabling Using LC Connectors

In today’s server networks, 10GbE has become commonplace. 10GbE multimode cabling with LC duplex connectors is the main infrastructure of 10GbE network. To leverage existing 10GbE cabling using LC connectors, the 40GBASE-SR QSFP+ Bi-Directional (BiDi) transceiver is an ideal choice for you. Used with WDM (Wavelength Division Multiplexing) technology, the 40GBASE-SR QSFP+ BiDi transceiver can support up to 100 meters with OM3 multimode fiber and up to 150 meters with OM4 multimode fiber cables with LC duplex connectors, allowing reuse of existing 10-Gbps fiber infrastructure for 40-Gbps connections so that helps reduce overall costs and installation time.

40GbE bidi


According to the above contents, we learned that the optics market for 40GbE connectivity is now relatively mature. Users can choose the most proper solution according to their network plan, requirements, and budget.



The QSFP+ transceiver is the dominant transceiver form factor used for 40GbE (Gigabit Ethernet) applications. In 2010 the IEEE standard 802.3ba released several 40GbE standard and along with the general specification, defined a number of fiber optic interfaces. These standard interfaces including 40GBASE-SR4 (QSFP SR4) and 40GBASE-LR4 (QSFP LR4) attempted to satisfy a number of different objectives including support for MMF (multimode fiber) and SMF (single-mode fiber) compatibility.

The basic versions of QSFP are SR4 and LR4 that are respectively designed for MMF and SMF 40GbE applications. SR is short for short reach and LR represents Long Reach. 4 means 4 Tx and Rx. The interfaces designed by 40GBASE-SR4 and 40GBASE-LR4 are not the same. The most obvious difference is that 40GBASE-SR4 is with MPO/MTP port while the 40GBASE-LR4 is with the Duplex LC port. The following table summarizes the differences between QSFP+ transceiver optical interfaces and electrical interfaces.


The cost of 40GBASE-SR4 QSFP+ is more cheaper than the 40GBASE-LR4 QSFP+. Additionally, the fiber cost of the cabling with them also have a big difference. Because smf cabling is more expensive than the mmf cabling.

With the wide deployment of 40 GbE, the 40GBASE-SR4 and 40GBASE-LR4 transceivers are more and more widely used. 40GBASE-LR4 QSFP+ transceivers (such as QSFP-40G-LR4) are most commonly deployed between data-center or IXP (Internet exchange point) sites with single-mode fiber. 40G SR4 QSFP+ transceivers (e.g. Cisco QSFP-40G-SR4) are used in data centers to interconnect two Ethernet switches with 8 fiber parallel OM3/OM4 multimode fiber cabling.

40G and 100G Pluggable Optics in the Data Center

40G and 100G Pluggable Optics in the Data Center

40G and 100G are in full swing this year. All the topics, news and product solutions are around 40G and 100G, especially the pluggable optics, including transceivers, Copper DACs (Direct Attach Cables) and AOCs (Active Optical Cables). In data center optics market, 40G optics are ubiquitous and 100G optics are accelerating.

Changes of Data Center Architectures and Connections
Data center is changing both in architectures and connections. Thus, products need upgrade to meet these changes.

Architecture Changes
Data centers are becoming larger, more modular and more homogenous. Networks migrate from traditional 3-tier to flattened 2-tier topology. Workloads spread across 10s, 100s, sometimes 1000s VMs and hosts. Driven by applications like Twitter, Facebook and Youtube, higher degree of east-west traffice across networks are required.


Connection Changes
Data center connections are moving from 1G and 10G, to 40G and 100G.
Within the data center rack—10G is being deployed and 25G is being standardized now. Thus, 40G and 50G may both be the next step.
Between data center racks—40G is being deployed now and 100G deployment will follow. So, the following step may be 200G or 400G.
Between data center buildings and WAN (Wide Area Network)—For long spans, 100G is being deployed and 400G is being standardized now. The following solution is expected as 800G, 1TE or 1.6TE.

40G and 100G Pluggable Optics in the Data Center

40G vs. 100G Within the Data Center
The most direct difference of 40G and 100G optics is the data rate. But actually, 40G and 100G optics have their own merits.

Characteristic of 40G Pluggable Optics

  • Lowest cost per bit
  • MMF reaches up to 300 m
  • Breaks out to 4 x 10G

Characteristic of 100G Pluggable Optics

  • Highest density per bit
  • Lowest power consumption/bit
  • MMF reaches up to 100m for now
  • Breaks out to 4 x 25GE

40G & 100G Pluggable Optics Overview
In today’s market, 40G products mainly include 40GBASE-SR4 and 40GBASE-LR4 QSFP+ modules and 40G AOCs. QSFP+ supports both 40G links between racks and high-density 10G links within the rack, especially the 40G QSFP+ breakout AOC which is an ideal solution for 40G migration.


100G is ready here. Tens of thousands of 100G Ethernet links deployed in core routers and carrier switches. Vast majority are CFP modules and CFP2 deployments are now starting. In addition,100G is rapidly expanding. For instance, new optical standards for the data center (100G SR4, CWDM4, PSM4) and new higher density 100G module form factors like CFP4 and QSFP28 are on the way. High port-count 100G switches are being designed and many 100G modules will be used to support high-density 10G and 25G. It is said that 100G and 4x 25G deployments are expected to grow substantially starting in 2015. 100G products mainly include 100GBASE-SR10 and 100GBASE-LR4 CFP/CFP2/CFP4 and 120G AOCs. Additionally, QSFP28 as the 100G module form factor of choice for new data center switches is also launched.


Large growth in web content and applications is driving such as growth in bandwidth and changes in data center traffic as well as growth in number of optical links. 40G and 100G optics development supports this growth with smaller module form factors for higher port density, lower power consumption per bit and lower cost per bit. Meanwhile, new link speeds like 25G, 50G, 200G and 400G are being standardized. The pluggable optics will continue to develop to further satisfy the data center requirement. Let’s look forward to it!

Comparison of 40GbE Connectivity Options

Comparison of 40GbE Connectivity Options

High speed and wide bandwidth demands drive data centers to consolidate into more complex systems. The speed of data center now is increasing to 40 Gbps and eventually to 100 Gbps. Thus, new optical technologies and cabling infrastructure are required. In this post, I will introduce some commonly used fiber optic cabling connectivity options for 40Gbps infrastructure.

Pluggable Optical Modules: 40G QSFP+ Transceivers
As we know, fiber optic transceiver is an electronic device that receives an electrical signal, converts it into a light signal, and launches the signal into a fiber. It also receives the light signal, from another transceiver, and converts it into an electrical signal. It is the key component in fiber optic transmission. The basic interface of 40G pluggable optical modules are 40GBASE-LR4 and 40GBASE-SR4 in QSFP+ form factor, such as Cisco QSFP-40G-LR4 and QSFP-40G-SR4.


40GBASE-LR4 QSFP+: 40GBASE-LR4 transceiver support with a link length up to 10 kilometers over 1310 nm single mode fiber, LC Connector. It is most commonly deployed between data-center or IXP sites with single mode fiber.

40GBASE-SR4 QSFP+: 40GBASE-SR4 transceivers are used in data centers to interconnect two Ethernet switches with 8 fiber parallel multimode fiber OM3/OM4 cables. It can support the transmission distance up to 100 m with OM3 fiber and 150 m with OM4 fiber. The optical interface of 40GBASE-SR4 QSFP+ is MPO/MTP.

In addition, for single-mode fiber transmission, there are 40GBASE-LR4 Parallel Single Mode (PSM) transceivers which are used to provide support for up to four 10Gbps Ethernet connections on a QSFP+ port over single mode fiber at distances up to 10 km. For multimode fiber transmission, QSFP+ extended SR4 transceivers are developed which is designed with optimized VCSEL with better performance of RMS spectral width compared with QSFP+ SR4. QSFP+ extended SR4 transceivers can support transmission distance up to 300 m with OM3 fiber and 400 m with OM4.

Passive & Active Direct Attach Copper Cables
The QSFP+ passive or active direct attach copper cables are designed with twinax copper cable and terminated with QSFP+ connectors. The main difference between passive QSFP+ DAC and active QSFP+ DAC is that the passive one is without the active component. They provide short distance (same shelf) inexpensive connectivity at up to 40Gbps rates and operate 4 independent 10G channels using the QSFP connector footprint. Each of the four channels can operate at multi-rate speeds Gigabit to 10Gbps.


Active Optical Cable (AOC) Assemblies
Active optical cable, namely AOC brings a more flexible cabling than direct attach copper cables with the advantages of lighter weigth, longer transmission distance and higher performance for anti-EMI. Now, 40G AOC assemblies are popular with users.


After introducing the basic options of 40G cabling connectivity, we take a conclusion for the above content in the following tables:



In addition, don’t forget there are some typical cabling components you will require when building 40G cabling, such as MTP trunk cables, MTP cassettes, LC to MTP jumpers and so on.

MTP Assemblies

Fiberstore offers a comprehensive solution for 40G fiber optic cabling connectivity. What’s more, products such as 40GBASE-LR4 and 40GBASE-SR4 QSFP+ modules are in stock and can shipped in 12hrs. For more information, please visit

Comparison of 40G QSFP+ LR4 and SR4 Optics

Comparison of 40G QSFP+ LR4 and SR4 Optics

At present, for 40GbE, there are several kinds of transmission solutions. People usually use the 4 x 10 GE Breakout cable, 40G QSFP+ module or 40G CFP modules to achieve the 40GbE. Among them, the first two kinds of solutions are most widely used for nowaday 40 Gigabit Ethernet. For aggregation and core native 40 GbE, the 40G QSFP+ module is an ideal choice. There are many different variants of 40G QSFP+ modules which are defined by IEEE 802.3ba to support different applications. 40GBASE-LR4 (40G-QSFP-LR4) and 40GBASE-SR4 (40G-QSFP-SR4) QSFP+ optics are the most commonly used specifications of 40G QSFP+ optics. So, what are the differences between them on the module structure and applications?

The IEEE 802.3ba committee ratified the 40 Gigabit Ethernet standard in June, 2010. Along with the general specification, it defined a number of fiber optic interfaces. These standard interfaces attempted to satisfy a number of different objectives including support for multi-mode fiber and single-mode fiber compatibility. 40BASE-LR4 and 40BASE-SR4 QSFP+ optics both comply the IEEE 802.3ba and QSFP Multisource Agreement (MSA), but for different applications according to their features and parameters. Here are some detailed differences between 40BASE-LR4 and 40BASE-SR4 QSFP+ modules.

  • 40GBASE-LR4 QSFP+ transceivers are most commonly deployed between data-center or IXP sites with single mode fiber.
  • 40GBASE-SR4 QSFP+ transceivers are used in data centers to interconnect two Ethernet switches with 12 lane ribbon OM3/OM4 cables.
Fiber Type and Connector
  • 40GBASE-LR4 QSFP+ transceivers support link lengths of up to 10 kilometers over a standard pair of G.652 single-mode fiber with duplex LC connectors.
  • 40GBASE-SR4 QSFP+ transceivers are generally enable high-bandwidth 40G optical links over 12-fiber parallel fiber terminated with MPO/MTP multifiber connectors.
QSFP+ connectors
Wavelength (nm)
  • 40GBASE-LR4 QSFP+ (Multiplexing and demultiplexing of the four wavelengths are managed within the device): 1271 nm, 1291 nm, 1311 nm, 1331 nm
  • 40GBASE-SR4 QSFP+: 4 x 850 nm
Transmission Distance
    – 10 km on single-mode– 4λ x 10G 1300 nm region
  • 40GBASE-SR4 QSFP+ (parallel optics)
    – 100 m on OM3–10G on 4 fibers per direction
    – 150 m on OM4 –10G on 4 fibers per direction

Obviously, the 40G QSFP LR4 is designed for long transmission used with single-mode fiber while 40G QSFP SR4 is for short distance with OM3/OM4. And “4” here means four lanes. Additionally, they are in different wavelengths and with different connectors. When they used in actual network, they are used different technology.

Ok, the article will be end here as today’s topic is simple. I hope that this post will give you some help and of course due to the limited knowledge of the author, there are some inevitable errors and omissions existing in this paper. Futhermore, if you are very interested in this topic and want to gain more information about it, I suggest you to read the IEEE 802.3ba and QSFP Multisource Agreement (MSA).

Related Recommendation

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