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Introduction to 100G QSFP28 Optical Transceiver

March 7, 2017

Nowadays, the trend for 100G Ethernet network is bullish and inevitable. Thus, the demands for 100G modules are becoming increasingly great. Among various 100G optical transceivers, QSFP28 100G optical transceiver is the most preferred module for smaller size and lower power consumption. Today, we will introduce you to all you need to know about QSFP 100G transceivers.

What Is 100G QSFP28 Optical Transceiver?

The following part will elaborate 100G QSFP28 transceivers in terms of four aspects: definition, module standards, laser types, transmission media & transmission distances.

Definition

The 100G QSFP28 optical transceiver is designed for 100 Gigabit Ethernet, EDR InfiniBand, or 32G Fibre Channel. It generally has the exact same footprint and faceplate density as 40G QSFP+. Just as the 40G QSFP+ is implemented using four 10Gbps lanes, the 100G QSFP28 module is implemented with four channels of high-speed differential signals with data rates ranging from 25Gbps up to potentially 40Gbps. With an upgrade electrical interface, the QSFP28 100G transceiver is capable of supporting signals up to 28Gbps. QSFP 100G SR4, QSFP 100G LR4, QSFP 100G PSM4, QSFP 100G CWDM4, and QSFP 100G ER4 are the five common types of 100G QSFP28 modules designed to meet the different transmission distance requirements. Compared with 100G CFP/CFP2/CFP4 transceivers, 100G QSFP28 optics surpass them with the strong ability to increase density, decrease power consumption, and decrease the price per bit.

Figure 1: 100G QSFP28 Optical Transceivers

Module Standards

The 100G QSFP28 optical module standards are mainly defined by two key organizations, namely IEEE and Multi Source Agreement (MSA). The QSFP28 SR4, QSFP28 LR4, QSFP28 ER4 are defined by the IEEE. How to clarify these three items from their names? The ‘QSFP’ means the form factor; ‘28’ represents that each lane has a maximum transmission rate of 28Gbps; ‘SR’ means short reach (100m), ‘LR’ is long reach (10km) and ‘ER’ is extended reach (40km). ‘4’ represents that the module has 4 lanes. For example, the QSFP28 LR4 means that it is a long reach 100G module which can transmit 100G signals over four wavelengths with a transmission distance of 10km.

100GBASE-SR4 and 100GBASE-LR4 are the most commonly used 100G interface specifications defined by the IEEE. However, the transmission distance of QSFP28 SR4 is too short to meet all interconnection requirements and the cost of QSFP28 LR4 is too high for large data centers. Therefore, MSA brought a solution for mid-range connectivity to the market and defined the standards of QSFP28 PSM4 and CWDM4. Although the capability of QSFP 100G LR4 completely covers QSFP28 CWDM4, but the QSFP 100G CWDM4 solution is much cheaper and more competitive than QSFP28 LR4 in the scenario of 2km transmission.

Laser Types

The laser plays an important role in the 100G QSFP28 optical transceivers which has five major types: VCSEL, FP, DFB, DML, and EML. Different types of lasers have different working wavelengths, modes and application environments.

Laser Type Wavelength Working Mode Application Scenario
VSCEL 850nm Surface Emitting Within 200m
FP 1310nm/1550nm Edge Emitting 500m-10km
DFB 1310nm/1550nm Edge Emitting 40km
DML 1310nm/1550nm Direct Modulated 500m-10km
EML 1310nm/1550nm Electro-absorption Modulated 40km

  • The VCSEL laser features small size, low power consumption, easy integration, low price and high coupling efficiency with multimode fibers, which is often used for QSFP28 SR4 modules.

  • The EML, with its small dispersion, large extinction and long-distance transmission, is designed to meet all those requirements for QSFP 100G LR4 and QSFP 100G ER4 transceivers.

  • The DML can realize signal modulation through the way of modulating the injection current of the laser. Thus, it is suitable for QSFP28 PSM4 and QSFP28 CWDM4 modules with a transmission distance of 500m or 2km.

Transmission Media & Transmission Distances

The 100G QSFP28 optical transceivers are equipped with LC duplex or MTP/MPO-12 connectors, which transmission distances vary from 70m to 40km. The transmission distances of the QSFP28 optics decide the application scenarios of them. All the QSFP28 100G transceivers can be applied to direct connection, interconnection in enterprises and data center networks. The following diagram shows the specific differences between QSFP 100G optics.

QSFP28 SR4 LR4 PSM4 CWDM4 ER4
Standards IEEE 802.3 IEEE 802.3 MSA MSA IEEE 802.3
Connector MTP/MPO-12 LC Duplex MTP/MPO-12 MTP/MPO-12 MTP/MPO-12
Cable Type MMF SMF SMF SMF SMF
Wavelength 850nm 1295.56-1309.14nm 1310nm 1270-1331nm 1295.56-1309.14nm
Transmission Distance 70/100m 10km 500m 2km 40km
Transmitter Type VCSEL EML DML/FP DML DML

QSFP28 Transceiver Application Guide

Nowadays, 100G optical QSFP28 transceivers account for a significant portion of networking construction. Due to their compact size, low power consumption, and high performance, 100G QSFP28 optics are mainly used for the following situations.


  • 100G Ethernet

  • Data Center Interconnect

  • Infiniband QDR and DDR interconnects

  • Enterprise networking

However, due to different properties and functions of various types, their exact application is based on the actual needs in real environment. QSFP28 100G SR4 is mainly applicable in a 100G data center with a demand for short transmission distance between 5m and 100m.

QSFP28 100G PSM4 and QSFP28 100G CWDM4 can are specially designed for network applications with a transmission distance of 500m and 2km. While QSFP28 100G CWDM4 is relatively more costly, it requires only two single-mode fibers for transceiving and transmitting in both directions, which is much less than the eight single-mode fibers of PSM4, making it a high-quality choice for Enterprise networking and 100G Ethernet.

QSFP28 100G LR4, generally used together with LC single-mode fiber cables, can reach a maximum transmission distance of 10km. It converts 4X25Gbps electrical signals into 4 LAN WDM optical signals and then multiplexes them into a single channel to realize 100G optical transmission.

QSFP28 100G ER4 supports the 100G data connection by using WDM multiplexing wavelength division technology. It can reach a maximum transmission distance of up to 40KM, making it a perfect choice for optical communication and applications compliant to Ethernet 100GBASE-ER4 Lite standard.

How to Select the Best QSFP28 Optics?

Now that we know we have to choose the best 100G optics based on our actual demand, but how? How can we choose the right one? Here is a selection guide for you.

For transmission distance between 5m and 100m, you can choose the QSFP28 SR4 optical transceiver module. It can transmits 70m using OM3 fibers or 100m using OM4 fibers.

For transmission distance between 100m to 2km, QSFP 100G PSM4 or QSFP28 CWDM4 modules would be better. The cost of QSFP28 CWDM4 is much higher than the QSFP28 PSM4. However, the QSFP28 CWDM4 requires only two single mode fibers in two-way transmission which is much less than the eight single mode fibers of QSFP28 PSM4, the total cost of the QSFP 100G PSM4 raises very quickly. In practical applications, it is necessary to decide whether to use QSFP28 PSM4 or QSFP28 CWDM4 depending on the interconnection distance.

For transmission distance between 10km to 40km, you can consider QSFP 100G LR4 which has a maximum transmission distance of up to 10 km or QSFP28 ER4 transceivers which can reach up a maximum transmission distance of even further—40km.

Conclusion

In summary, all 100G QSFP28 optical transceivers are equipped with high-port density and low power consumption characteristics which is an ideal alternative for large scale data centers, as well as future network expansions. FS offers all kinds of 100G QSFP28 modules that run through programming and an extensive series of platform diagnostic tests to ensure their performance and compatibility. For more information, please do not hesitate to visit fs.com.

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