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Introduction to 10GbE/25GbE/40GbE/100GbE Fiber Optic Cabling

Introduction to 10GbE/25GbE/40GbE/100GbE Fiber Optic Cabling

Technology is changing rapidly. Just when you got used to Gigabit Ethernet speeds being a fast & reliable system, someone unveiled 10GbE, 25GbE, 40GbE or even 100GbE systems a few years later. The newer and higher performing iterations are indeed the great breakthrough for telecommunication industry, but also pose difficulty in choosing network migration path—10G to 40G to 100G, or to 25G to 50G to 100G. We have described 10G, 25G, 40G and 100G Ethernet technology before, now in this blog, we’d like to introduce the four fiber optic cabling, and compare two 100G migration paths.

Cost-effective 10GbE Fiber Optic Cabling

10 Gigabit Ethernet technology defined by IEEE 802.3ae-2002 standard, is matured nowadays. Just like the “old” Gigabit Ethernet, 10Gb network can be terminated with either copper or fiber cabling. 1000BASE-T standard usually uses the Cat5e cables as the transmission media, while 10GbE bandwidth requires high grade copper cables like Cat6/Cat6a/Cat7 cables to support 10Gbps data rate. For instance, 10G SFP+ 10GBASE-T transceiver modules utilize Ethernet copper cables (Cat6a/Cat7) for a link length of 30m. SFP+ direct attach cables (DAC) and active optical cables (AOC) are also regarded as the cost-effective solutions for 10G short-reach applications. Besides 10G copper cables, there are single-mode (OS2) and multimode fiber patch cables (OM3/OM4) applied to different 10GbE IEEE standards. For the detailed information about the 10G cabling options, please see the following table.

10G fiber optic cable

As to the 10G fiber optic transceivers, there are a series of optical form factors including the XENPAK, X2, XFP, SFP+. The former three 10GbE optical transceivers were released earlier than smaller 10G form factor—SFP+ module. However, owing to their larger footprint, they are not successful on the 10G hardware market. Furthermore, SFP+ optics, compliant with several IEEE standards (SR, LR, LRM, ER, ZR and 10GBASE-T…) wins the heart of 10G end-users.

Singe-lane Design Makes 25GbE Shine

When 25G Ethernet was developed to support a single-lane 25Gbps standard in 2014, it was treated as the “new” 10GbE technology but delivers 2.5 times more data. Compared to 40GbE that was based on 10GbE, 25GbE with one lane obviously improves the port density and cost requirement. 25GbE network can support both copper and fiber optic cables, seen in the below table.Similar to 10GbE networks, 25G Ethernet physical interface specification supports several 25Gbps capable form factors, including CFP/CFP2/CFP4, SFP28 (1×25 Gbps) and QSFP28 (4×25 Gbps), which is also used for 100GbE. SFP28 25GBASE-SR and 25GBASE-LR SFP28 are two popular 25GbE optical transceiver modules available on the market, the former supports up to 100m link length while the latter allows a maximum transmission distance of 10 km.

25G optical modules

The available optical switches of the market do not support direct 25GbE connections using an SFP28 direct attach copper (DAC) cable. It is recommended to use a breakout cable that allows four 25GbE ports to connect to a 100GbE QFSFP28 switch port. FS.COM SFP28 DAC cable lengths are limited to four meters (1m, 2m, 3m, 5m) for 25GbE. And if you prefer a longer length, the 25GbE active optic cable (AOC) solutions are good recommendations.

25G Optics SFP28 Type
All 25G SFP28 Ports 25GBASE-SR 50µm MMF / 70m
25GBASE-LR 9µm SMF / 10km
25GBASE-AOC Pre-terminated in 3, 5, 7, 10, 15, 20, 25, 30m lengths
25G Copper SFP28 Type Media/Reach
All 25G SFP28 Ports 25GBASE-CR Twinax / ‘Direct Attach’ Pre-terminated in 1m, 2m, 3m, 5m lengths


Fast & Reliable 40GbE Fiber Optic Cabling

Like the 10GbE fiber optic cabling, there are several IEEE standards of 40GbE transceiver in the whole evolution. 40G QSFP+ optical transceivers are the most commonly used optics for 40G network. So how to choose fiber optic cables for 40G optical transceivers? The following table will help you out.

40G modules

Besides the QSFP+ fiber transceivers and fiber optic cables, 40G DAC cables available in QSFP+ DAC cables and AOC cables enable short-reach options. For 40G cabling, QSFP+ to QSFP+ (40G to 40G) and QSFP+ to 4SFP+ (40G to 10G) breakout cables satisfy customers for various fiber types and reach requirements.

100GbE Fiber Optic Cabling For Future Proofing

With the price of 100G optics cutting down in 2017, 100GbE network is no longer out of customers’ reach. Telecom giants like Cisco, Arista, HPE launches series of 100G optical switches to meet the market demand. And for other 100G components like 100G optical transceivers, fiber patch cables, racks & enclosures, etc, those are ubiquitous on the market.

100G optical transceivers including the CFP, CFP2, CFP4, CXP and the most popular 100G QSFP28 optics in IEEE standards provide a great selection to the overall users.For 100G inter-rack connections, QSFP28 to QSF28 Direct Attach Copper (DAC) Cables and Active Optical Cables (AOC) as well as the QSFP28 to SFP28 breakout cables are the cost-effective solutions.

Path 1: 10G to 40G to 100G

Many of the largest data centers has already moved to 40GbE, which are constructed out of 4 parallel SerDes 10Gb/s links between the Ethernet chip and the QSFP pluggable. The short-reach QSFP interfaces (QSFP+ SR4 modules) use 4 pair of fiber between them, and the copper Direct Attach Cable (DAC) equivalent carry the same on several copper cables inside the big cable. Longer-reach QSFP interfaces (QSFP+ LR4 optics) put the 4 10Gb/t streams onto separate Wave Division Multiplexing (WDM) waves which can be carried over a single pair of fiber. This is part of the reason why QSFP optics are fairly expensive still, especially for longer distances.10GbE to 40GbE to 100GbESimilarly for the 100GbE interfaces that are available today, these are really constructed out of 10 parallel paths of 10Gb/t streams. 100G SR10 modules is the optical transceiver modules that support 10×10Gb/s modes. But neither the CXP SR10 modules or CFP 100G SR10 optics are not popular on the 100G hardware market owing to their larger form factors. Eventually, they need to utilize the smaller footprint 100G modules—QSFP28 transceiver, which is mentioned above as the optical transceivers that can be used in 25GbE and 100GbE.

Result: Although the migration path from 10G to 40G to 100G requires more ports and increases cost per bit, 40GbE between switches is expected to be remain and will not be affected in the near future.

Path 2: 25G to 100G—The Move From 10 Lanes to 4

The old transition path of Ethernet has increased by 10X in speed like the 10G to 40G to 100G. However, 25 Gbps over a single lane for server makes 100G migration be 4×25Gb/s mode.100-gbe-block-diagramUsing four-lane variants like QSFP28 is more economical in several ways:

  • The single-lane design makes four 25 Gbps lanes transceivers less expensive than ten 10Gbps lanes because the transceiver is simpler and less costly to manufacture.
  • The power required to run SFP28 transceivers is much less than required for a typical 10-lane transceiver, it is the same case as the cooling costs.
  • For fiber connections, moving from 10GbE to 40GbE may require an upgrade to four times the number of fibers (MPO), but a 25GbE connection does not because it is the same as 10GbE (single TX and single RX, not four each for TX and RX).
  • Moving from 10GbE to 40GbE typically requires a forklift upgrade to thicker, more expensive cables, but a 25GbE direct attach copper connection does not.

Result: There are few switches and NIC cards that directly support 25GbE. But the curve for 25GbE won’t fade away, rapid development and pre-standard 25GbE products coming soon!


This article introduces 10G/40G/100G fiber optic cabling, and make a clear comparison between the two paths to 100GbE. Customers prefer 4×25Gbps for the reasons: Less parallel paths, less fibers, less optics, less everything. For those who want to upgrade from 40G to 100G, appreciate the reliable performance of 40G with the potential to run across 2 parallel 25Ghz rather than 4 required today.



100 Gigabit Ethernet is popular in data center optics market this year. We have discussed much about 100G optics in the previous articles. In this blog, we are going to make a comparison between the two main physical layer standards for short reach interconnection—100GBASE-SR10 (CFP) and 100GBASE-SR4 (QSFP28 SR4) from several aspects.

Transceiver Form Factors Comparison

CFP is the typical representative form factor of 100GBASE-SR10. It is specified by a MSA (Multi-Source Agreement) between competing manufacturers. The CFP was designed after the SFP (Small Form-Factor Pluggable) interface, but is significantly larger to support 100 Gbps, using 10 x 10Gbps lanes.

QSFP28 is the latest 100G form factor. QSFP28 utilizes four 25G electrical lanes each to support the latest 100/50/25G transceivers and interconnects. Thus, it is the representative form factor of 100GBASE-SR4.


Result: QSFP28 form factor is more popular than CFP now, according to the surge shipment of QSFP28 optics.

Size Comparison

Transceivers with 100GBASE-SR4 and 100GBASE-SR10 interface respectively correspond to QSFP28 and CFP. Thus they have a significant difference in size. See the picture below, CFP is much larger than QSFP28. Obviousely, CFP is not much suitable for high density applications. In contrast, QSFP28 increases front-panel density and decrease power and price per bit.


Result: As high density is becoming one of the trends of data center, QSFP28 (100GBASE-SR4) is much more suitable to meet this demand than CFP (100GBASE-SR10).

Electrical and Optical Lanes Diagram

The following diagram shows the basic principles of 100GBASE-SR4 and 100GBASE-SR10:



Result: 100GBASE-SR4 has higher speed per channel with less channels so that it can decrease the port density.

Cables & Connectors Options

Both 100GBASE-SR4 and 100GBASE-SR10 optics use laser optimized multimode fiber (OM3/OM4) for transmission. But 100GBASE-SR4 optics (such as Cisco 100G-QSFP28-SR4) uses a 12-fiber standard QSFP MPO/MTP cable for connectivity (4 Tx and 4 Rx, each lane providing 25 Gbps of throughput) while 100GBASE-SR10 optics use a 2×12-fiber or 24-fiber strand MPO/MTP cable for connectivity (10 Tx and 10 Rx, each lane providing 10 Gbps of throughput).


Because optics with 100GBASE-SR4 and 100GBASE-SR10 interface can be respectively breakout to 4×25 Gbps and 10×10 Gbps, it is easy to upgrade from 25GbE/10 GbE to 100 GbE using MPO/MTP to LC harness cable.

Result: 100GBASE-SR4 uses 12-fiber MPO/MTP while 100GBASE-SR10 uses two 12-fiber or one 24-fiber MPO/MTP. For 100G point-to-point interconnection, the 100GBASE-SR4 is more cost-effective. For network migration, 100GBASE-SR4 is also better since it has less breakout legs which greatly reduce the cost of cable management.


100GBASE-SR4 offers layout advantages to the host board implementer and substantial cable plant fiber count reduction while being competitive with 100GBASE-SR10 in cost and power consumption.

Why QSFP28 Transceivers So Popular?

Why QSFP28 Transceivers So Popular?

Since last year, the 100G market has risen. All media and networks believe that this year will be the year of 100 GbE. QSFP28, as a new form factor, becomes more and more popular in the 100G transceiver market. The surge in shipment of QSFP28 transceivers makes us wonder that why QSFP28 transceivers are so popular.

Brief Introduction to QSFP28

QSFP28 transceiver is designed for 100G speeds and using the 4×25 wiring specification. Now, technology of QSFP28 is relatively matured. With the movement to reduce costs, the QSFP28 transceivers become increasing popular in the market. Similar to 40G QSFP+ that is implemented using four 10Gbps lanes, the QSFP28 uses four 25Gbps lanes with parallel technology, eliminating the costly gearbox found in the other version of 100G transceivers like CFP, CFP2, and the CPAK. Additionally, the QSFP28 transceiver has an upgraded electrical interface to support signaling up to 28Gbps signals, yet keeps all of the physical dimensions of its predecessor.

Two basic versions of QSFP28 transceivers are 100GBASE-SR4 QSFP28 transceiver and 100GBASE-LR4 QSFP28 transceiver that are respectively used for multimode (MMF) and single-mode (SMF) 100G applications. The working principles of these two type of QSFP28 transceivers are shown below:


Why QSFP28 Transceivers So Popular?

The QSFP28 makes deploying 100GbE (or beyond) networks as easy as 10GbE networks, having a strong ability to increase density, decrease power consumption, and decreases price per bit. It is fast becoming the universal and preferred data center form factor for several reasons shown in the following:

The QSFP+ has the same form factor and maximum number of ports with QSFP+, but the lane speeds are increased to 2.5X. Thus, the QSFP28 increases front-panel density over QSFP+.

There are limitations of the other versions of 100G transceivers. For example, in the first generation of 100GbE switches and routers, the smaller CXP form factor was used for cabling and the CFP or CFP2 was used for transceivers. This forced huge equipment design sacrifices. A switch with CXP ports couldn’t be used in a data center with single-mode fiber (SMF). A router using CFP2 or CPAK ports had bandwidth limited by the 8-10 ports that could fit on the front panel.

QSFP28 solves these issues because it supports both cables and transceivers. With QSFP28, a one rack-unit switch can accommodate up to 36 QSFP ports. Many more varieties of transceivers and cables can plug into these ports. The cables can be either copper direct attach cables (DACs) or active optical cables (AOCs).

What’s more, the QSFP28 transceivers can use either VCSELs (useful for shorter distances on MMF) or silicon photonics (for longer distances on SMF). Silicon photonics enables QSFP28 transceivers to support any data center reach up to 10 kilometers, and provides a high degree of integration. Silicon photonics is low power; even WDM (Wavelength Division Multiplexing) designs can fit within the 3.5W maximum of QSFP.


According to the current market trends, the QSFP28 has great market prospect. And the coming generations of high-bandwidth switches, routers, and adapters will all feature QSFP28 ports to better adapt the 100G (or beyond) network demands.

Are 100G Transceivers Suitable for Modern 100GbE Network & High-Density Data Center?

Are 100G Transceivers Suitable for Modern 100GbE Network & High-Density Data Center?

Since 2010, the 100GbE transceivers have begun to appear on the market. After 5 years of evolution, 100G transceivers are becoming more and more suitable for the modern 100GbE network and the high-density data center. What evolution are there in the last 5 years? And what’s the nowadays mainstream 100GbE transceiver?

We divide the 100GbE development as three generation by 2022. The first generation 100GbE transceivers include the innovators 1-2 premium ports/slot 1st generation CFP modules (2010/2011) and 2-4 premium ports/slot 2nd generation CFP modules (2012/2013). Since last year, we have entered to the 2nd generation 100GbE transceivers age. 4-8 lower-cost ports/slots CFP2 modules have gradually replaced the CFP. Today, CFP4 and QSFP28 modules with smaller size and lower cost are more popular in the market. So, how about the 3rd generation 100GbE transceivers? The time will show you. But it is no doubt that the 3rd generation 100GbE transceivers will be more suitable for the requirement of the future 100GbE network, maybe with more than 24-48 ports/slots serial design.


By the end of 2015, 100GbE equipment will be widely deployed. As Andrew Schmitt, research director for carrier transport networking at IHS Infonetics said: “Next year (2016) is going to be huge for 100GbE.” Thus, the prospect of the 100GbE transceivers market will be better. At the same time, the development of 100GbE transceivers will be faster.

As we describe above, today, two new form factors are competing to become the successor to CFP and CFP2: CFP4 and QSFP 28. What’s the difference of them and which is better? CFP4 is slightly wider and longer than QSFP28 while both are about four times smaller than the original CFP. Both support modules of less than 6W of power consumption. In fact, QSFP28 can even achieve 3.5W. Despite the size and performance advantages of QSFP28, stacking it is more difficult than belly-to-belly CFP4 due to heat, signal integrity and EMI considerations. But, if the manufacturer is willing and able to cope with the stacking challenge, QSFP28 is indeed the superior choice. The remaining mystery is: who will be first to achieve 40KM distances, if anybody.

No matter which type of 100GbE transceivers will be the winner of future 100GbE network, the size of 100GbE transceiver modules will be smaller to be suitable to the high-density data center and the cost will be lower to save the project budget. Let’s look forward to it.

What’s Difference Between CFP and CXP Transceivers?

What’s Difference Between CFP and CXP Transceivers?

Two years ago, though everyone is talking about the 100G Ethernet as the next generation, it had still faced a lot of problems to be solved, seeming to be a long way off. But, technologies are developed very rapidly, and now 100G Ethernet is becoming more and more closer to us. Fiber connectivity in higher-speed active equipment is being condensed and simplified with plug-and-play, hot-swap transceiver miniaturization. Thus, optical transceiver technology is one of the basic but important technology to achieve the realiable and effective 100G Ethernet. Interfaces for 100G active equipment include CFP and CXP. So, what are CFP and CXP? And what’s the difference between CFP and CXP (CFP vs CXP)? Is CXP transceiver designed to replace the CFP? … You might be interested in them and have a lot of questions in your mind. Today, you will find the answer in this post.

About CFP
cfp-100g85-1m-ju-01CFP, short for C form-factor pluggable, is a multi-source agreement to produce a common form-factor for the transmission of high-speed digital signals. The c stands for the Latin letter C used to express the number 100 (centum), since the standard was primarily developed for 100 Gigabit Ethernet systems. In fact, CFP also supports the 40GbE. When talking about CFP, we always define it as multipurpose CFP, compared to the CXP which is discussed later.

The CFP MSA was formally launched at OFC/NFOEC 2009 in March by founding members Finisar, Opnext, and Sumitomo/ExceLight. The CFP form factor, as detailed in the MSA, supports both single-mode and multi-mode fiber and a variety of data rates, protocols, and link lengths, including all the physical media-dependent (PMD) interfaces encompassed in the IEEE 802.3ba standard. At 40GE, target optical interfaces include the 40GBase-SR4 for 100 meters (m) and the 40GBase-LR4 for 10 kilometers (km). There are three PMDs for 100 GE: 100GBase-SR10 for 100 m, 100GBase-LR4 for 10 km, and 100GBase-ER4 for 40 km.

CFP was designed after the Small Form-factor Pluggable transceiver (SFP) interface, but is significantly larger to support 100Gbps. The electrical connection of a CFP uses 10 x 10Gbps lanes in each direction (RX, TX). The optical connection can support both 10 x 10Gbps and 4 x 25Gbps variants. CFP transceivers can support a single 100Gbps signal like 100GE or OTU4 or one or more 40Gbps signals like 40GE, OTU3, or STM-256/OC-768.

The CFP-MSA Committee has defined three form factors:

  • CFP – Currently at standard revision 1.4 and is widely available in the market
  • CFP2 – Currently at draft revision 0.3 is half the size of the CFP transceiver; these are recently available in the market
  • CFP4 – Standard is not yet available, is half the size of a CFP2 transceiver, not yet available

CFP transceiver today to future

The original CFP specification was proposed at a time when 10Gbps signals were far more achievable than 25Gbps signals. As such to achieve 100Gbps line rate, the most affordable solution was based on 10 lanes of 10Gbps. However as expected, improvements in technology has allowed higher performance and higher density. Hence the development of the CFP2 and CFP4 specifications. While electrical similar, they specify a form-factor of 1/2 and 1/4 respectively in size of the original specification. Note that CFP, CFP2 and CFP4 modules are not interchangable (but would be interoperable at the optical interface with approriate connectors).

About CXP
CXPCXP is targeted at the clustering and high-speed computing markets, so we usually called it high-density CXP. Technically, the CFP will work with multimode fiber for short-reach applications, but it is not really optimized in size for the multimode fiber market, most notably because the multimode fiber market requires high faceplate density. The CXP was created to satisfy the high-density requirements of the data center, targeting parallel interconnections for 12x QDR InfiniBand (120 Gbps), 100 GbE, and proprietary links between systems collocated in the same facility. The InfiniBand Trade Association is currently standardizing the CXP.

The CXP is 45 mm in length and 27 mm in width, making it slightly larger than an XFP. It includes 12 transmit and 12 receive channels in its compact package. This is achieved via a connector configuration similar to that of the CFP. For perspective, the CXP enables a front panel density that is greater than that of an SFP+ running at 10 Gbps.

Typical applications of CXP in the data center include 100GE over Copper (DAC with CXP connectors): 7m (23ft) and 100GE over multimode fiber: CXP for short reach applications (CFP is used for longer reach applications).

What’s the difference between CFP and CXP?
Despite having a similar acronym and emerging at roughly the same time, the CFP and CXP form factors are markedly different in terms of size, density, and intended application. The CFP and CXP optical transceiver form factors are hot pluggable, both feature transmit and receive functions, and both support data rates of 40 and 100 Gbps. But the similarities begin and end there. Aimed primarily at 40- and 100-Gigabit Ethernet (GbE) applications, the CFP supports both singlemode and multimode fiber and can accommodate a host of data rates, protocols, and link lengths. The CXP, by contrast, is targeted at the clustering and high-speed computing markets. The two are therefore complementary, not competitive, according to several sources. Thus, the existence of CXP does not mean the replacing of CFP.

However, things are never black and white. In some case, there is a competition between CFP and CXP, as CFP can also be used with multimode fiber. It becomes more of a choice for system vendors. Do they need to build a box that can adapt to any interface? If so, they would probably use CFP. If it’s a box that is just focused on the short-reach market, then they would probably use something more like CXP.

I hope this post will let you more understanding the 100GbE transceivers, whether CFP or CXP. Similarly, you could kown the 40GbE transceiver through this post as the CFP and CXP also support the 40GbE. If you want to have a further study on this subject, I suggest you to learn the related refference of MSA. If you have any requirement of the related products, please contact us over