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Tutorial/8 Facts That Help You Select 100G QSFP28 Application for IDC

8 Facts That Help You Select 100G QSFP28 Application for IDC

Interfaces and application technologies that support the 100G  data network are very diverse and unique, which are likely to confuse users about the deployment of the 100G application in the data center. You may have questions like which one is the best when technology, update, return on investment are taken into account. Fortunately, some recommendations will be offered in the following parts.

10G/40G/100G Data Connection Solution

1. Current Situation of 100G Application

Since the release of the IEEE802.3ba standard in 2010, the application of 100G has been technically feasible overall. At the same time, discussions on the application and technology of 100G have also attracted much attention.  However, 100G networking supported by single-mode or multi-mode fiber technology in IEEE802.3ba has not evolved into a large-scale application world. This has something with the way the early standard multi-mode fiber applications transit 100G through parallel 10G*10 channels, and the way single Mode fiber based on WDM technology supports long-distance.

In addition, it is also caused by the high cost of the combination of 100G optical transceiver and fiber link, the large power consumption in port, and especially the disparity between interfaces and fiber channels in 100G and 40G based on Multi-mode fiber. Therefore, the actual market demand for 100G has not been stimulated so far.

However, through the 2-3 years of development, 100G applications have been supported by a variety of technologies and alliances, no matter the standardized IEEE802.3bm or organizations like SWDM or MSA, which announces their 100G application models.

2. Market Potential for Data Center 100G Application

The IEEE802.3ba standard was released in 2010, while the large-scale application of 40G based on multimode optical fiber parallel transmission actually started in the second half of 2013, during which some users chose 40G application supported by BIDI technology.  40G application market has been stabilized on the whole after the recent years of substantial deployment. In contrast, the 100G application in scale will be in a full swing. Is this true? The answer is yes because the user’s demand for the 100G application currently does exist.

The chart below is The forecast of the Ethernet port trend from DELL, and it shows that the application of 100G was gaining momentum after 2016.

Fiber Ethernet Switch Ports in Building and Data Center(in million ports)

The trend of Global Ethernet Switch Port

3. Factors that Promote the 100G Ethernet Application in Scale

 ● Increasing Data Communication  

From a macro perspective, data communication has been growing rapidly in recent years. According to a Cisco report, the compound annual growth rate of global mobile network data communication is 57%; the one of Internet of Things (IoT) investment growth in the Chinese market is more than 30%. The IoT’s rapid development makes the data communication in  MTM(Machine to Machine) soar and a lot of traffic are in constant need and even 24 hours a day.

  ● Investment Growth in broadband network

According to the statistic, the compound annual growth rate of investment in network convergence has reached around 15%. In addition to the predictable data trends mentioned above, there will be a lot of applications backed by internet technologies that will promote the rapid growth of global IP-based data communications.  A compound annual growth rate of 25% and a larger proportion in cloud computing data centers are clearly shown in the chart below.

Comparison Betweeen Traditional Data center and Clouding Center in Zettabytes

Source: Cisco Global Cloud Index, 2014–2019

   ● Technical Support of Cloud Computing and Virtualization  

The rapid development of the application mentioned above all relies on the support of data center network technology. The server utilization in Cloud computing data center can be significantly improved in the back of cloud computing and virtualization technology.

According to statistics in a Cisco forecast report, the global cloud computing data center server load is more than 2.6 times that of the conventional data center server load, and the annual gap is still widening.

   ● The Evolution of IEEE802.3by Standard

The IEEE P802.3by Task Force is defining server port specifications for 25 Gb/s transmissions over a medium like multi-mode fiber (MMF), Twinax direct attach copper (DAC) cable, and will release upcoming technologies like 25GBase-T and 40GBase-T, which are based on Cat8 cables. When a 10G server port is updated to 25G, the backbone connection between the access layer network and the core network in a data center requires a 100G network synchronouslySo does the connection between Spine and Leaf in a virtual data center.  Multi-mode fiber transmission of 25G per channel is equivalent to separating a single transmission channel in the IEEE803.3bm standard. It is an irresistible trend to realize the application of service port 25G in terms of market and technology. 

4. Users with an Urgent Need for 100G Application

The demand varies in the data center, for not all users in the data center is in need of the 100G networking application.

But do you have any idea what types of data center express their demand the most? To answer this question, we can divide data centers into two categories, IDC (Internet Data Center) and EDC (Enterprise Data Center). Relatively speaking, the former is more urgent for deploying 100G backbone networks. Specifically, they include some huge internet companies, data centers in operators, larger-scale cloud computing data centers as well as some big EDCs(Enterprise Date Centers)

5. Main Application Models of 100G in Data Centers

 There are various 100G interface technologies available in the market. However, the distances between joint points are less than 500 meters in most data centers, unless parts in the campus backbone of super data centers. Considering the fact, we will choose the most likely applied four interface models for 100G and make further analysis of their features. Hope the information below will be meaningful to you.

 Type 1: 100G QSFP28-SR4

Compliant with the new standard IEEE802.3bm officially released in 2015, the 100G QSFP28 SR4 utilizes four channels composed of an 8-fiber MMF for parallel transmission and each channel features 25Gbps. As MMF, both OM3 and OM4 support 100 applications with an MPO connector of 12 fibers, among which four fibers in the middle are not required to be used. Besides, its transmission model fully complies with 40GBase-SR4 specifications in IEEE802.3ba and a QSFP28 transceiver is needed. The channels and interfaces are shown as follows:

100G QSFP28-SR4 transport model and interface

                                                                                                       100G QSFP28-SR4 transport model and interface

At present, some mainstream optical transceiver manufacturers are promoting 100GBase-eSR4 in terms of the increased luminous power to enhance the transmission distance. 100GBase-eSR4 is expected to achieve a transmission distance of 200 meters based on OM4 fiber to reach the coverage of most data center backbone applications. Meanwhile, this 100GBase eSR4 module will eliminate the transmission bottleneck over parallel multimode fiber and significantly improve the feasibility of QSFP28 SR4 optic connectors.



Type 2: 100G QSFP28-SWDM4

The SWDM, also known as Short Wavelength Division Multiplexing, is a technology that adopts 1-core MMF to transmit optical signals at four wavelength ranges, of which the center wavelength is 850nm, 880nm, 910nm, and 940nm. Similar to CWDM applied to a single-mode fiber (SMF), it applies the wavelength division multiplexing technology to the short wavelength range on MMF. The following figure illustrates how the signal is transmitted based on 100G QSFP28-SWDM4.

100G Base-SWDM4 Transmission Principle

100G Base-SWDM4 Transmission Principle

The conventional OM3 and OM4 MMF(Multi-Mode Fiber) is designed to be work at the wavelength of 850 nm, but the SWDM technology demands four windows. It means four wavelength ranges shall be used for signal transmission, which suggests that a vertical-cavity surface-emitting laser (VCSEL) with its high-performance is still deployed. To improve the overall bandwidth, the new-generation WBMMF, also known as Wideband Multimode Fiber, would improve the bandwidth performance with a peak up to around 880nm wavelength, which is higher than that of the conventional OM4 MMF. The following figure is a comparison between these two fibers:

Source from OFS

Bandwidth vs.Wavelength: Standard & Broad Bandwidth OM4

In compliance with 50/125um and TIA-492AAAE standard and, WBMMF can be backward compatible with conventional OM3 and OM4 fibers. The latter can also be used as the transmission medium for SWDM, but its transmission distance is shorter than that of the WBMMF. SWDM technology has not yet fully disclosed and is being promoted by a couple of membership companies from SWDM Alliance, which is mainly composed of network equipment manufacturers and optical module equipment manufacturers. 100G Base-SWDM4 optical modules are designed with small-size QSFP28 connectors to support the higher bandwidth density for switch panels.

Type 3: 100G QSFP28-PSM4

100G QSFP28-PSM4 utilizes a parallel SMF for transmission. Its 8-core SMF builds four independent channels for 100Gbps optical interconnects, and each channel is capable of 25Gbps. It supports 12-fiber  MTP/MPO (APC) connector, among which the four fibers in the middle are not used either. The transmission mode of 100G QSFP28-PSM4 is similar to that of 100GBase-SR4, but the biggest difference is that PSM4 uses SMF as the media and a laser for the light source at 1310nm wavelength. It also supports a QSFP28 transceiver. Please refer to the following figure to know how it transmits signals:

100G QSFP28-PSM4 Transmission Principle

100G QSFP28-PSM4 Transmission Principle

Type 4 100G QSFP28-CWDM4

Based on the coarse wavelength division multiplexing, the 100Gbase-CWDM4 interface adopts a laser source over SMF with a duplex LC connector and cable. Second, each fiber supports four wavelength ranges, of which the center wavelength are 1271nm, 1291nm, 1311nm, and 1331nm. Third, every wavelength supports 25Gbps so that an aggregate bandwidth of 100Gbps can be realized.

It also adopts QSFP28 transceivers. Last, unlike a traditional and high-cost transceiver for 10km over SMF, the cost of its transceivers for 2km is more competitive. The interface model is illustrated as follows:

100G QSFP28-IR4 operating principle

100G QSFP28-CWDM4 Transmission Principle

100G QSFP28-CWDM4 Transmission Principle

6. Features of Mainstream 100G Optical Modules

   ● 100G QSFP28-SR4: The interface is identical to QSFP-40G-SR4, which is connected to a QSFP28 optical transceiver through an MTP / MPO fiber connector. The original MTP / MPO physical fiber link can be directly upgraded for 100G applications. Regular OM3 and OM4 MMF feature 70m and 100m transmission respectively for 100G applications.     


  ● 100G QSFP28-SWDM4: This module includes three main characteristics; first, this interface, which supports a QSFP28 optical transceiver uses a 2- fiber duplex LC connector. Second, it enables 300m transmission over WBMMF and at least 100m transmission over OM4 for 100G. Last, compared with the SR4 model, the 100G QSFP28 PSM4 model demands only 25 percent of its fibers.


 ●100G QSFP28-PSM4: this type of model transmits 100G data with its single-mode MTP/MPO optic fiber connector. Designed with built-in QSFP28 interfaces, 100G QSFP28 PSM4 utilizes regular OS2 SM to realize a transmission reach up to 500m, which makes its overall price competitive. However, it is not acknowledged by the IEEE organization and is popularized by the PSM4 MSA.


   ● 100G QSFP28-CWDM4: It also adopts QSFP28 transceivers. Unlike a traditional and high-cost transceiver for 10km over SMF, the cost of this transceiver for 2km is more competitive. However, it is not acknowledged by the IEEE organization either and is popularized by the PSM4 MSA.

7. Comparison between the 4 Typical 100G QSFP28 Interface Models

    ●  Technological Difference

    Based on the four interfaces, the technological difference between the four 100G application models mentioned above is shown in the following chart.

    Technological comparison between 4 100G QSFP28 Optical Modules

    It is obvious that 100G BASE-PSM4 and 100G BASE-CWDM4 share some similarities in terms of standard, fiber type, and transceiver, while 100G BASE-SR4 and 100G BASE-SWDM4 are distinctive from each other in regards to a few aspects like standard, interface, and max. link length.

     ● Cost Difference

    From an optical transceiver structure viewpoint, SR4 is the most cost-effective, though its wiring layout cost is relatively high.  And CWDM4's cost is higher than the other 3 types.

    100G Optical Transceivers Links: SR4 vs PSM4 vs CWDM4 vs SWDM

     100G Optical Transceivers Links: SR4 vs PSM4 vs CWDM4 vs SWDM

    PSM4 can be more cost-effective because it uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. However, from an infrastructure viewpoint, this transceiver would be more expensive when the link distance is long, mainly due to the fact that it uses 8 optical SMFs while 100G QSFP28 CWDM4 uses only 2 optical single-mode-fibers.


    When considering the above two factors, the total cost comparison can be qualitatively shown in the figure below. PSM4 starts with a lower cost due to its lower transceiver cost, but as the link distance increases, its total cost climbs up very fast due to the fact that it uses 8 optical fibers.

    The relation between Link Distance &Total Cost

     The relation between Link Distance &Total Cost

    The overall price difference between QSFP28 PSM4 and SWDM is not significant. As the SWDM Alliance is composed of a small number of optical transceiver manufacturers, it is not an open technology at present. The market price for the time being remains relatively high, but in terms of technology and cost composition, SWDM short wave division multiplexing technology has a large price reduction space, this product in the future has certain market potential.

    8. The prospects of the100G QSFP28 for Data Centers

      ● 100G QSFP28-SR4

    Based on the relevant analysis above, it may be easily inferred that  100G QSFP28 SR4 enjoys a prospective market in the future. This can be analyzed in the following aspects: first, from the perspective of the IEEE802.3 standard organization, 100G Base-SR4 is currently a standardized application, while the other three products have not yet been approved by the IEEE802.3 standard organization.

    Second, SR4 can directly support 100G data center applications through MTP/MPO to LC breakout cables comprised of 8 fibers or 4 duplex channels. It has four independent channels for 100Gbps optical interconnects, and each channel is capable of 25Gbps, which can unify different interfaces in switches and cut the cost of traffic utilization.

    Third, base on the comparison among the 4 typical models, the overall price of 100G QSFP28-SR4 is currently one of the most cost-effective solutions. Last but not least, based on the existing 40GBase-SR4 cabling system, SR4’s cabling system can be directly upgraded to meet the demand for 100G, making it the preferred solution to the 40G data center upgrade.


    ● 100G QSFP28 -SWDM4
    100G Base-SWDM4 is potential due to its capacity to achieve regular 100G speed thanks to SWDM technology, which can reduce the number of fibers by 75%. This is manageable when it comes to simplifying the cabling system and is feasible for applications with higher density.     

    Besides, QSFP28 SWDM technology supports longer transmission distances. The optical fiber using WBMMF is expected to reach a distance of 300 meters, which is suitable for the backbone distance requirements of most data centers.


    Moreover, the cost of 100G QSFP28 -SWDM optical transceivers supported by VCSEL light source Has little difference from that of the 100G QSFP28-SR4. Though you may find that the price is 30-50% higher than the SR4 in the current market, it has an edge in terms of technology.


    SWDM’s market share is not as large as the SR4’s during the inception of 100G. However, it is predicted that the 100G BaseSWDM application will increase exponentially in the subsequent phase. Compared with the current situation that more users pick up the SR4 for the data center’s update and capacity expansion, some users from the brand-new data center would prefer the SWDM products.

    ● 100G QSFP28-PSM4
    Compared with applications based on MMF, 100GBase-PSM4 transmits data over parallel single-mode optical fiber with a link distance of at least 500 meters, which can meet the requirements of 98% of the data center backbone. Unlike the expensive conventional single-mode transceivers, transceivers(both active and passive) backed by PSM4 technology are cost-competitive partly due to the lower cost of SMF than the MMF. This can be better exemplified if the average length of trunk meters exceeds 300 meters.


    It is predicted that PSM4 will obtain some shares in the 100G market, especially for users of large data centers or some Internet IDCs. However, its SMF interface based on MTP/MPO is more susceptible to the environment, making its on-site maintenance more costly. In addition, the significant cost reduction in QSFP28 PSM4 is rarely seen. Therefore, all of these drawbacks may prevent it from the mainstream in the 100G application market.

     100G QSFP28-CWDM4

    100G QSFP28-CWDM4 distinct itself from the other 3 types by its longer link distance, which can reach up to 2KM. It is suitable for ultra-large-scale data center backbone applications and 100G connections between the backbones of data center buildings in the data center industrial park.


    The fact that 100G QSFP28-CWDM4, also known as QSFP28-100G-IR4 has not been approved by the IEEE standardization organization has refrained it from being the mainstream application in 100G data center. But it will be part of the niche market in the backbone application of the ultra-large-scale 100G data center.


    100G is well underway currently. Research firm ISH Infornetics has reported that  100G makes up more than half of optical transceiver transmission in the data centers. By implementing 100G, operators of large-scale data centers improve their networking efficiency and gain faster transmission speed. There are various interface technologies about 100G applications in the market.  How do you plan to prepare your network? How do you build out your cabling system that supports the 100G application? We wish the above analysis of the 4 typical 100G applications based on their technologies, costs, and marketing prospects is meaningful for your 100G networking plan.